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 // SPDX-License-Identifier: (LGPL-2.1 OR BSD-2-Clause)
 /* Copyright (c) 2022 Meta Platforms, Inc. and affiliates. */
 #include <ctype.h>
 #include <stdio.h>
 #include <stdlib.h>
 #include <string.h>
 #include <libelf.h>
 #include <gelf.h>
 #include <unistd.h>
 #include <linux/ptrace.h>
 #include <linux/kernel.h>
 
 /* s8 will be marked as poison while it's a reg of riscv */
 #if defined(__riscv)
 #define rv_s8 s8
 #endif
 
 #include "bpf.h"
 #include "libbpf.h"
 #include "libbpf_common.h"
 #include "libbpf_internal.h"
 #include "hashmap.h"
 
 /* libbpf's USDT support consists of BPF-side state/code and user-space
  * state/code working together in concert. BPF-side parts are defined in
  * usdt.bpf.h header library. User-space state is encapsulated by struct
  * usdt_manager and all the supporting code centered around usdt_manager.
  *
  * usdt.bpf.h defines two BPF maps that usdt_manager expects: USDT spec map
  * and IP-to-spec-ID map, which is auxiliary map necessary for kernels that
  * don't support BPF cookie (see below). These two maps are implicitly
  * embedded into user's end BPF object file when user's code included
  * usdt.bpf.h. This means that libbpf doesn't do anything special to create
  * these USDT support maps. They are created by normal libbpf logic of
  * instantiating BPF maps when opening and loading BPF object.
  *
  * As such, libbpf is basically unaware of the need to do anything
  * USDT-related until the very first call to bpf_program__attach_usdt(), which
  * can be called by user explicitly or happen automatically during skeleton
  * attach (or, equivalently, through generic bpf_program__attach() call). At
  * this point, libbpf will instantiate and initialize struct usdt_manager and
  * store it in bpf_object. USDT manager is per-BPF object construct, as each
  * independent BPF object might or might not have USDT programs, and thus all
  * the expected USDT-related state. There is no coordination between two
  * bpf_object in parts of USDT attachment, they are oblivious of each other's
  * existence and libbpf is just oblivious, dealing with bpf_object-specific
  * USDT state.
  *
  * Quick crash course on USDTs.
  *
  * From user-space application's point of view, USDT is essentially just
  * a slightly special function call that normally has zero overhead, unless it
  * is being traced by some external entity (e.g, BPF-based tool). Here's how
  * a typical application can trigger USDT probe:
  *
  * #include <sys/sdt.h>  // provided by systemtap-sdt-devel package
  * // folly also provide similar functionality in folly/tracing/StaticTracepoint.h
  *
  * STAP_PROBE3(my_usdt_provider, my_usdt_probe_name, 123, x, &y);
  *
  * USDT is identified by it's <provider-name>:<probe-name> pair of names. Each
  * individual USDT has a fixed number of arguments (3 in the above example)
  * and specifies values of each argument as if it was a function call.
  *
  * USDT call is actually not a function call, but is instead replaced by
  * a single NOP instruction (thus zero overhead, effectively). But in addition
  * to that, those USDT macros generate special SHT_NOTE ELF records in
  * .note.stapsdt ELF section. Here's an example USDT definition as emitted by
  * `readelf -n <binary>`:
  *
  *   stapsdt              0x00000089       NT_STAPSDT (SystemTap probe descriptors)
  *   Provider: test
  *   Name: usdt12
  *   Location: 0x0000000000549df3, Base: 0x00000000008effa4, Semaphore: 0x0000000000a4606e
  *   Arguments: -4@-1204(%rbp) -4@%edi -8@-1216(%rbp) -8@%r8 -4@$5 -8@%r9 8@%rdx 8@%r10 -4@$-9 -2@%cx -2@%ax -1@%sil
  *
  * In this case we have USDT test:usdt12 with 12 arguments.
  *
  * Location and base are offsets used to calculate absolute IP address of that
  * NOP instruction that kernel can replace with an interrupt instruction to
  * trigger instrumentation code (BPF program for all that we care about).
  *
  * Semaphore above is and optional feature. It records an address of a 2-byte
  * refcount variable (normally in '.probes' ELF section) used for signaling if
  * there is anything that is attached to USDT. This is useful for user
  * applications if, for example, they need to prepare some arguments that are
  * passed only to USDTs and preparation is expensive. By checking if USDT is
  * "activated", an application can avoid paying those costs unnecessarily.
  * Recent enough kernel has built-in support for automatically managing this
  * refcount, which libbpf expects and relies on. If USDT is defined without
  * associated semaphore, this value will be zero. See selftests for semaphore
  * examples.
  *
  * Arguments is the most interesting part. This USDT specification string is
  * providing information about all the USDT arguments and their locations. The
  * part before @ sign defined byte size of the argument (1, 2, 4, or 8) and
  * whether the argument is signed or unsigned (negative size means signed).
  * The part after @ sign is assembly-like definition of argument location
  * (see [0] for more details). Technically, assembler can provide some pretty
  * advanced definitions, but libbpf is currently supporting three most common
  * cases:
  *   1) immediate constant, see 5th and 9th args above (-4@$5 and -4@-9);
  *   2) register value, e.g., 8@%rdx, which means "unsigned 8-byte integer
  *      whose value is in register %rdx";
  *   3) memory dereference addressed by register, e.g., -4@-1204(%rbp), which
  *      specifies signed 32-bit integer stored at offset -1204 bytes from
  *      memory address stored in %rbp.
  *
  *   [0] https://sourceware.org/systemtap/wiki/UserSpaceProbeImplementation
  *
  * During attachment, libbpf parses all the relevant USDT specifications and
  * prepares `struct usdt_spec` (USDT spec), which is then provided to BPF-side
  * code through spec map. This allows BPF applications to quickly fetch the
  * actual value at runtime using a simple BPF-side code.
  *
  * With basics out of the way, let's go over less immediately obvious aspects
  * of supporting USDTs.
  *
  * First, there is no special USDT BPF program type. It is actually just
  * a uprobe BPF program (which for kernel, at least currently, is just a kprobe
  * program, so BPF_PROG_TYPE_KPROBE program type). With the only difference
  * that uprobe is usually attached at the function entry, while USDT will
  * normally will be somewhere inside the function. But it should always be
  * pointing to NOP instruction, which makes such uprobes the fastest uprobe
  * kind.
  *
  * Second, it's important to realize that such STAP_PROBEn(provider, name, ...)
  * macro invocations can end up being inlined many-many times, depending on
  * specifics of each individual user application. So single conceptual USDT
  * (identified by provider:name pair of identifiers) is, generally speaking,
  * multiple uprobe locations (USDT call sites) in different places in user
  * application. Further, again due to inlining, each USDT call site might end
  * up having the same argument #N be located in a different place. In one call
  * site it could be a constant, in another will end up in a register, and in
  * yet another could be some other register or even somewhere on the stack.
  *
  * As such, "attaching to USDT" means (in general case) attaching the same
  * uprobe BPF program to multiple target locations in user application, each
  * potentially having a completely different USDT spec associated with it.
  * To wire all this up together libbpf allocates a unique integer spec ID for
  * each unique USDT spec. Spec IDs are allocated as sequential small integers
  * so that they can be used as keys in array BPF map (for performance reasons).
  * Spec ID allocation and accounting is big part of what usdt_manager is
  * about. This state has to be maintained per-BPF object and coordinate
  * between different USDT attachments within the same BPF object.
  *
  * Spec ID is the key in spec BPF map, value is the actual USDT spec layed out
  * as struct usdt_spec. Each invocation of BPF program at runtime needs to
  * know its associated spec ID. It gets it either through BPF cookie, which
  * libbpf sets to spec ID during attach time, or, if kernel is too old to
  * support BPF cookie, through IP-to-spec-ID map that libbpf maintains in such
  * case. The latter means that some modes of operation can't be supported
  * without BPF cookie. Such mode is attaching to shared library "generically",
  * without specifying target process. In such case, it's impossible to
  * calculate absolute IP addresses for IP-to-spec-ID map, and thus such mode
  * is not supported without BPF cookie support.
  *
  * Note that libbpf is using BPF cookie functionality for its own internal
  * needs, so user itself can't rely on BPF cookie feature. To that end, libbpf
  * provides conceptually equivalent USDT cookie support. It's still u64
  * user-provided value that can be associated with USDT attachment. Note that
  * this will be the same value for all USDT call sites within the same single
  * *logical* USDT attachment. This makes sense because to user attaching to
  * USDT is a single BPF program triggered for singular USDT probe. The fact
  * that this is done at multiple actual locations is a mostly hidden
  * implementation details. This USDT cookie value can be fetched with
  * bpf_usdt_cookie(ctx) API provided by usdt.bpf.h
  *
  * Lastly, while single USDT can have tons of USDT call sites, it doesn't
  * necessarily have that many different USDT specs. It very well might be
  * that 1000 USDT call sites only need 5 different USDT specs, because all the
  * arguments are typically contained in a small set of registers or stack
  * locations. As such, it's wasteful to allocate as many USDT spec IDs as
  * there are USDT call sites. So libbpf tries to be frugal and performs
  * on-the-fly deduplication during a single USDT attachment to only allocate
  * the minimal required amount of unique USDT specs (and thus spec IDs). This
  * is trivially achieved by using USDT spec string (Arguments string from USDT
  * note) as a lookup key in a hashmap. USDT spec string uniquely defines
  * everything about how to fetch USDT arguments, so two USDT call sites
  * sharing USDT spec string can safely share the same USDT spec and spec ID.
  * Note, this spec string deduplication is happening only during the same USDT
  * attachment, so each USDT spec shares the same USDT cookie value. This is
  * not generally true for other USDT attachments within the same BPF object,
  * as even if USDT spec string is the same, USDT cookie value can be
  * different. It was deemed excessive to try to deduplicate across independent
  * USDT attachments by taking into account USDT spec string *and* USDT cookie
  * value, which would complicated spec ID accounting significantly for little
  * gain.
  */
 
 #define USDT_BASE_SEC ".stapsdt.base"
 #define USDT_SEMA_SEC ".probes"
 #define USDT_NOTE_SEC  ".note.stapsdt"
 #define USDT_NOTE_TYPE 3
 #define USDT_NOTE_NAME "stapsdt"
 
 /* should match exactly enum __bpf_usdt_arg_type from usdt.bpf.h */
 enum usdt_arg_type {
     USDT_ARG_CONST,
     USDT_ARG_REG,
     USDT_ARG_REG_DEREF,
 };
 
 /* should match exactly struct __bpf_usdt_arg_spec from usdt.bpf.h */
 struct usdt_arg_spec {
     __u64 val_off;
     enum usdt_arg_type arg_type;
     short reg_off;
     bool arg_signed;
     char arg_bitshift;
 };
 
 /* should match BPF_USDT_MAX_ARG_CNT in usdt.bpf.h */
 #define USDT_MAX_ARG_CNT 12
 
 /* should match struct __bpf_usdt_spec from usdt.bpf.h */
 struct usdt_spec {
     struct usdt_arg_spec args[USDT_MAX_ARG_CNT];
     __u64 usdt_cookie;
     short arg_cnt;
 };
 
 struct usdt_note {
     const char *provider;
     const char *name;
     /* USDT args specification string, e.g.:
      * "-4@%esi -4@-24(%rbp) -4@%ecx 2@%ax 8@%rdx"
      */
     const char *args;
     long loc_addr;
     long base_addr;
     long sema_addr;
 };
 
 struct usdt_target {
     long abs_ip;
     long rel_ip;
     long sema_off;
     struct usdt_spec spec;
     const char *spec_str;
 };
 
 struct usdt_manager {
     struct bpf_map *specs_map;
     struct bpf_map *ip_to_spec_id_map;
 
     int *free_spec_ids;
     size_t free_spec_cnt;
     size_t next_free_spec_id;
 
     bool has_bpf_cookie;
     bool has_sema_refcnt;
 };
 
 struct usdt_manager *usdt_manager_new(struct bpf_object *obj)
 {
     static const char *ref_ctr_sysfs_path = "/sys/bus/event_source/devices/uprobe/format/ref_ctr_offset";
     struct usdt_manager *man;
     struct bpf_map *specs_map, *ip_to_spec_id_map;
 
     specs_map = bpf_object__find_map_by_name(obj, "__bpf_usdt_specs");
     ip_to_spec_id_map = bpf_object__find_map_by_name(obj, "__bpf_usdt_ip_to_spec_id");
     if (!specs_map || !ip_to_spec_id_map) {
         pr_warn("usdt: failed to find USDT support BPF maps, did you forget to include bpf/usdt.bpf.h?\n");
         return ERR_PTR(-ESRCH);
     }
 
     man = calloc(1, sizeof(*man));
     if (!man)
         return ERR_PTR(-ENOMEM);
 
     man->specs_map = specs_map;
     man->ip_to_spec_id_map = ip_to_spec_id_map;
 
     /* Detect if BPF cookie is supported for kprobes.
      * We don't need IP-to-ID mapping if we can use BPF cookies.
      * Added in: 7adfc6c9b315 ("bpf: Add bpf_get_attach_cookie() BPF helper to access bpf_cookie value")
      */
     man->has_bpf_cookie = kernel_supports(obj, FEAT_BPF_COOKIE);
 
     /* Detect kernel support for automatic refcounting of USDT semaphore.
      * If this is not supported, USDTs with semaphores will not be supported.
      * Added in: a6ca88b241d5 ("trace_uprobe: support reference counter in fd-based uprobe")
      */
     man->has_sema_refcnt = access(ref_ctr_sysfs_path, F_OK) == 0;
 
     return man;
 }
 
 void usdt_manager_free(struct usdt_manager *man)
 {
     if (IS_ERR_OR_NULL(man))
         return;
 
     free(man->free_spec_ids);
     free(man);
 }
 
 static int sanity_check_usdt_elf(Elf *elf, const char *path)
 {
     GElf_Ehdr ehdr;
     int endianness;
 
     if (elf_kind(elf) != ELF_K_ELF) {
         pr_warn("usdt: unrecognized ELF kind %d for '%s'\n", elf_kind(elf), path);
         return -EBADF;
     }
 
     switch (gelf_getclass(elf)) {
     case ELFCLASS64:
         if (sizeof(void *) != 8) {
             pr_warn("usdt: attaching to 64-bit ELF binary '%s' is not supported\n", path);
             return -EBADF;
         }
         break;
     case ELFCLASS32:
         if (sizeof(void *) != 4) {
             pr_warn("usdt: attaching to 32-bit ELF binary '%s' is not supported\n", path);
             return -EBADF;
         }
         break;
     default:
         pr_warn("usdt: unsupported ELF class for '%s'\n", path);
         return -EBADF;
     }
 
     if (!gelf_getehdr(elf, &ehdr))
         return -EINVAL;
 
     if (ehdr.e_type != ET_EXEC && ehdr.e_type != ET_DYN) {
         pr_warn("usdt: unsupported type of ELF binary '%s' (%d), only ET_EXEC and ET_DYN are supported\n",
             path, ehdr.e_type);
         return -EBADF;
     }
 
 #if __BYTE_ORDER__ == __ORDER_LITTLE_ENDIAN__
     endianness = ELFDATA2LSB;
 #elif __BYTE_ORDER__ == __ORDER_BIG_ENDIAN__
     endianness = ELFDATA2MSB;
 #else
 # error "Unrecognized __BYTE_ORDER__"
 #endif
     if (endianness != ehdr.e_ident[EI_DATA]) {
         pr_warn("usdt: ELF endianness mismatch for '%s'\n", path);
         return -EBADF;
     }
 
     return 0;
 }
 
 static int find_elf_sec_by_name(Elf *elf, const char *sec_name, GElf_Shdr *shdr, Elf_Scn **scn)
 {
     Elf_Scn *sec = NULL;
     size_t shstrndx;
 
     if (elf_getshdrstrndx(elf, &shstrndx))
         return -EINVAL;
 
     /* check if ELF is corrupted and avoid calling elf_strptr if yes */
     if (!elf_rawdata(elf_getscn(elf, shstrndx), NULL))
         return -EINVAL;
 
     while ((sec = elf_nextscn(elf, sec)) != NULL) {
         char *name;
 
         if (!gelf_getshdr(sec, shdr))
             return -EINVAL;
 
         name = elf_strptr(elf, shstrndx, shdr->sh_name);
         if (name && strcmp(sec_name, name) == 0) {
             *scn = sec;
             return 0;
         }
     }
 
     return -ENOENT;
 }
 
 struct elf_seg {
     long start;
     long end;
     long offset;
     bool is_exec;
 };
 
 static int cmp_elf_segs(const void *_a, const void *_b)
 {
     const struct elf_seg *a = _a;
     const struct elf_seg *b = _b;
 
     return a->start < b->start ? -1 : 1;
 }
 
 static int parse_elf_segs(Elf *elf, const char *path, struct elf_seg **segs, size_t *seg_cnt)
 {
     GElf_Phdr phdr;
     size_t n;
     int i, err;
     struct elf_seg *seg;
     void *tmp;
 
     *seg_cnt = 0;
 
     if (elf_getphdrnum(elf, &n)) {
         err = -errno;
         return err;
     }
 
     for (i = 0; i < n; i++) {
         if (!gelf_getphdr(elf, i, &phdr)) {
             err = -errno;
             return err;
         }
 
         pr_debug("usdt: discovered PHDR #%d in '%s': vaddr 0x%lx memsz 0x%lx offset 0x%lx type 0x%lx flags 0x%lx\n",
              i, path, (long)phdr.p_vaddr, (long)phdr.p_memsz, (long)phdr.p_offset,
              (long)phdr.p_type, (long)phdr.p_flags);
         if (phdr.p_type != PT_LOAD)
             continue;
 
         tmp = libbpf_reallocarray(*segs, *seg_cnt + 1, sizeof(**segs));
         if (!tmp)
             return -ENOMEM;
 
         *segs = tmp;
         seg = *segs + *seg_cnt;
         (*seg_cnt)++;
 
         seg->start = phdr.p_vaddr;
         seg->end = phdr.p_vaddr + phdr.p_memsz;
         seg->offset = phdr.p_offset;
         seg->is_exec = phdr.p_flags & PF_X;
     }
 
     if (*seg_cnt == 0) {
         pr_warn("usdt: failed to find PT_LOAD program headers in '%s'\n", path);
         return -ESRCH;
     }
 
     qsort(*segs, *seg_cnt, sizeof(**segs), cmp_elf_segs);
     return 0;
 }
 
 static int parse_vma_segs(int pid, const char *lib_path, struct elf_seg **segs, size_t *seg_cnt)
 {
     char path[PATH_MAX], line[PATH_MAX], mode[16];
     size_t seg_start, seg_end, seg_off;
     struct elf_seg *seg;
     int tmp_pid, i, err;
     FILE *f;
 
     *seg_cnt = 0;
 
     /* Handle containerized binaries only accessible from
      * /proc/<pid>/root/<path>. They will be reported as just /<path> in
      * /proc/<pid>/maps.
      */
     if (sscanf(lib_path, "/proc/%d/root%s", &tmp_pid, path) == 2 && pid == tmp_pid)
         goto proceed;
 
     if (!realpath(lib_path, path)) {
         pr_warn("usdt: failed to get absolute path of '%s' (err %d), using path as is...\n",
             lib_path, -errno);
         libbpf_strlcpy(path, lib_path, sizeof(path));
     }
 
 proceed:
     sprintf(line, "/proc/%d/maps", pid);
     f = fopen(line, "r");
     if (!f) {
         err = -errno;
         pr_warn("usdt: failed to open '%s' to get base addr of '%s': %d\n",
             line, lib_path, err);
         return err;
     }
 
     /* We need to handle lines with no path at the end:
      *
      * 7f5c6f5d1000-7f5c6f5d3000 rw-p 001c7000 08:04 21238613      /usr/lib64/libc-2.17.so
      * 7f5c6f5d3000-7f5c6f5d8000 rw-p 00000000 00:00 0
      * 7f5c6f5d8000-7f5c6f5d9000 r-xp 00000000 103:01 362990598    /data/users/andriin/linux/tools/bpf/usdt/libhello_usdt.so
      */
     while (fscanf(f, "%zx-%zx %s %zx %*s %*d%[^\n]\n",
               &seg_start, &seg_end, mode, &seg_off, line) == 5) {
         void *tmp;
 
         /* to handle no path case (see above) we need to capture line
          * without skipping any whitespaces. So we need to strip
          * leading whitespaces manually here
          */
         i = 0;
         while (isblank(line[i]))
             i++;
         if (strcmp(line + i, path) != 0)
             continue;
 
         pr_debug("usdt: discovered segment for lib '%s': addrs %zx-%zx mode %s offset %zx\n",
              path, seg_start, seg_end, mode, seg_off);
 
         /* ignore non-executable sections for shared libs */
         if (mode[2] != 'x')
             continue;
 
         tmp = libbpf_reallocarray(*segs, *seg_cnt + 1, sizeof(**segs));
         if (!tmp) {
             err = -ENOMEM;
             goto err_out;
         }
 
         *segs = tmp;
         seg = *segs + *seg_cnt;
         *seg_cnt += 1;
 
         seg->start = seg_start;
         seg->end = seg_end;
         seg->offset = seg_off;
         seg->is_exec = true;
     }
 
     if (*seg_cnt == 0) {
         pr_warn("usdt: failed to find '%s' (resolved to '%s') within PID %d memory mappings\n",
             lib_path, path, pid);
         err = -ESRCH;
         goto err_out;
     }
 
     qsort(*segs, *seg_cnt, sizeof(**segs), cmp_elf_segs);
     err = 0;
 err_out:
     fclose(f);
     return err;
 }
 
 static struct elf_seg *find_elf_seg(struct elf_seg *segs, size_t seg_cnt, long virtaddr)
 {
     struct elf_seg *seg;
     int i;
 
     /* for ELF binaries (both executables and shared libraries), we are
      * given virtual address (absolute for executables, relative for
      * libraries) which should match address range of [seg_start, seg_end)
      */
     for (i = 0, seg = segs; i < seg_cnt; i++, seg++) {
         if (seg->start <= virtaddr && virtaddr < seg->end)
             return seg;
     }
     return NULL;
 }
 
 static struct elf_seg *find_vma_seg(struct elf_seg *segs, size_t seg_cnt, long offset)
 {
     struct elf_seg *seg;
     int i;
 
     /* for VMA segments from /proc/<pid>/maps file, provided "address" is
      * actually a file offset, so should be fall within logical
      * offset-based range of [offset_start, offset_end)
      */
     for (i = 0, seg = segs; i < seg_cnt; i++, seg++) {
         if (seg->offset <= offset && offset < seg->offset + (seg->end - seg->start))
             return seg;
     }
     return NULL;
 }
 
 static int parse_usdt_note(Elf *elf, const char *path, GElf_Nhdr *nhdr,
                const char *data, size_t name_off, size_t desc_off,
                struct usdt_note *usdt_note);
 
 static int parse_usdt_spec(struct usdt_spec *spec, const struct usdt_note *note, __u64 usdt_cookie);
 
 static int collect_usdt_targets(struct usdt_manager *man, Elf *elf, const char *path, pid_t pid,
                 const char *usdt_provider, const char *usdt_name, __u64 usdt_cookie,
                 struct usdt_target **out_targets, size_t *out_target_cnt)
 {
     size_t off, name_off, desc_off, seg_cnt = 0, vma_seg_cnt = 0, target_cnt = 0;
     struct elf_seg *segs = NULL, *vma_segs = NULL;
     struct usdt_target *targets = NULL, *target;
     long base_addr = 0;
     Elf_Scn *notes_scn, *base_scn;
     GElf_Shdr base_shdr, notes_shdr;
     GElf_Ehdr ehdr;
     GElf_Nhdr nhdr;
     Elf_Data *data;
     int err;
 
     *out_targets = NULL;
     *out_target_cnt = 0;
 
     err = find_elf_sec_by_name(elf, USDT_NOTE_SEC, &notes_shdr, &notes_scn);
     if (err) {
         pr_warn("usdt: no USDT notes section (%s) found in '%s'\n", USDT_NOTE_SEC, path);
         return err;
     }
 
     if (notes_shdr.sh_type != SHT_NOTE || !gelf_getehdr(elf, &ehdr)) {
         pr_warn("usdt: invalid USDT notes section (%s) in '%s'\n", USDT_NOTE_SEC, path);
         return -EINVAL;
     }
 
     err = parse_elf_segs(elf, path, &segs, &seg_cnt);
     if (err) {
         pr_warn("usdt: failed to process ELF program segments for '%s': %d\n", path, err);
         goto err_out;
     }
 
     /* .stapsdt.base ELF section is optional, but is used for prelink
      * offset compensation (see a big comment further below)
      */
     if (find_elf_sec_by_name(elf, USDT_BASE_SEC, &base_shdr, &base_scn) == 0)
         base_addr = base_shdr.sh_addr;
 
     data = elf_getdata(notes_scn, 0);
     off = 0;
     while ((off = gelf_getnote(data, off, &nhdr, &name_off, &desc_off)) > 0) {
         long usdt_abs_ip, usdt_rel_ip, usdt_sema_off = 0;
         struct usdt_note note;
         struct elf_seg *seg = NULL;
         void *tmp;
 
         err = parse_usdt_note(elf, path, &nhdr, data->d_buf, name_off, desc_off, &note);
         if (err)
             goto err_out;
 
         if (strcmp(note.provider, usdt_provider) != 0 || strcmp(note.name, usdt_name) != 0)
             continue;
 
         /* We need to compensate "prelink effect". See [0] for details,
          * relevant parts quoted here:
          *
          * Each SDT probe also expands into a non-allocated ELF note. You can
          * find this by looking at SHT_NOTE sections and decoding the format;
          * see below for details. Because the note is non-allocated, it means
          * there is no runtime cost, and also preserved in both stripped files
          * and .debug files.
          *
          * However, this means that prelink won't adjust the note's contents
          * for address offsets. Instead, this is done via the .stapsdt.base
          * section. This is a special section that is added to the text. We
          * will only ever have one of these sections in a final link and it
          * will only ever be one byte long. Nothing about this section itself
          * matters, we just use it as a marker to detect prelink address
          * adjustments.
          *
          * Each probe note records the link-time address of the .stapsdt.base
          * section alongside the probe PC address. The decoder compares the
          * base address stored in the note with the .stapsdt.base section's
          * sh_addr. Initially these are the same, but the section header will
          * be adjusted by prelink. So the decoder applies the difference to
          * the probe PC address to get the correct prelinked PC address; the
          * same adjustment is applied to the semaphore address, if any.
          *
          *   [0] https://sourceware.org/systemtap/wiki/UserSpaceProbeImplementation
          */
         usdt_abs_ip = note.loc_addr;
         if (base_addr)
             usdt_abs_ip += base_addr - note.base_addr;
 
         /* When attaching uprobes (which is what USDTs basically are)
          * kernel expects file offset to be specified, not a relative
          * virtual address, so we need to translate virtual address to
          * file offset, for both ET_EXEC and ET_DYN binaries.
          */
         seg = find_elf_seg(segs, seg_cnt, usdt_abs_ip);
         if (!seg) {
             err = -ESRCH;
             pr_warn("usdt: failed to find ELF program segment for '%s:%s' in '%s' at IP 0x%lx\n",
                 usdt_provider, usdt_name, path, usdt_abs_ip);
             goto err_out;
         }
         if (!seg->is_exec) {
             err = -ESRCH;
             pr_warn("usdt: matched ELF binary '%s' segment [0x%lx, 0x%lx) for '%s:%s' at IP 0x%lx is not executable\n",
                 path, seg->start, seg->end, usdt_provider, usdt_name,
                 usdt_abs_ip);
             goto err_out;
         }
         /* translate from virtual address to file offset */
         usdt_rel_ip = usdt_abs_ip - seg->start + seg->offset;
 
         if (ehdr.e_type == ET_DYN && !man->has_bpf_cookie) {
             /* If we don't have BPF cookie support but need to
              * attach to a shared library, we'll need to know and
              * record absolute addresses of attach points due to
              * the need to lookup USDT spec by absolute IP of
              * triggered uprobe. Doing this resolution is only
              * possible when we have a specific PID of the process
              * that's using specified shared library. BPF cookie
              * removes the absolute address limitation as we don't
              * need to do this lookup (we just use BPF cookie as
              * an index of USDT spec), so for newer kernels with
              * BPF cookie support libbpf supports USDT attachment
              * to shared libraries with no PID filter.
              */
             if (pid < 0) {
                 pr_warn("usdt: attaching to shared libraries without specific PID is not supported on current kernel\n");
                 err = -ENOTSUP;
                 goto err_out;
             }
 
             /* vma_segs are lazily initialized only if necessary */
             if (vma_seg_cnt == 0) {
                 err = parse_vma_segs(pid, path, &vma_segs, &vma_seg_cnt);
                 if (err) {
                     pr_warn("usdt: failed to get memory segments in PID %d for shared library '%s': %d\n",
                         pid, path, err);
                     goto err_out;
                 }
             }
 
             seg = find_vma_seg(vma_segs, vma_seg_cnt, usdt_rel_ip);
             if (!seg) {
                 err = -ESRCH;
                 pr_warn("usdt: failed to find shared lib memory segment for '%s:%s' in '%s' at relative IP 0x%lx\n",
                     usdt_provider, usdt_name, path, usdt_rel_ip);
                 goto err_out;
             }
 
             usdt_abs_ip = seg->start - seg->offset + usdt_rel_ip;
         }
 
         pr_debug("usdt: probe for '%s:%s' in %s '%s': addr 0x%lx base 0x%lx (resolved abs_ip 0x%lx rel_ip 0x%lx) args '%s' in segment [0x%lx, 0x%lx) at offset 0x%lx\n",
              usdt_provider, usdt_name, ehdr.e_type == ET_EXEC ? "exec" : "lib ", path,
              note.loc_addr, note.base_addr, usdt_abs_ip, usdt_rel_ip, note.args,
              seg ? seg->start : 0, seg ? seg->end : 0, seg ? seg->offset : 0);
 
         /* Adjust semaphore address to be a file offset */
         if (note.sema_addr) {
             if (!man->has_sema_refcnt) {
                 pr_warn("usdt: kernel doesn't support USDT semaphore refcounting for '%s:%s' in '%s'\n",
                     usdt_provider, usdt_name, path);
                 err = -ENOTSUP;
                 goto err_out;
             }
 
             seg = find_elf_seg(segs, seg_cnt, note.sema_addr);
             if (!seg) {
                 err = -ESRCH;
                 pr_warn("usdt: failed to find ELF loadable segment with semaphore of '%s:%s' in '%s' at 0x%lx\n",
                     usdt_provider, usdt_name, path, note.sema_addr);
                 goto err_out;
             }
             if (seg->is_exec) {
                 err = -ESRCH;
                 pr_warn("usdt: matched ELF binary '%s' segment [0x%lx, 0x%lx] for semaphore of '%s:%s' at 0x%lx is executable\n",
                     path, seg->start, seg->end, usdt_provider, usdt_name,
                     note.sema_addr);
                 goto err_out;
             }
 
             usdt_sema_off = note.sema_addr - seg->start + seg->offset;
 
             pr_debug("usdt: sema  for '%s:%s' in %s '%s': addr 0x%lx base 0x%lx (resolved 0x%lx) in segment [0x%lx, 0x%lx] at offset 0x%lx\n",
                  usdt_provider, usdt_name, ehdr.e_type == ET_EXEC ? "exec" : "lib ",
                  path, note.sema_addr, note.base_addr, usdt_sema_off,
                  seg->start, seg->end, seg->offset);
         }
 
         /* Record adjusted addresses and offsets and parse USDT spec */
         tmp = libbpf_reallocarray(targets, target_cnt + 1, sizeof(*targets));
         if (!tmp) {
             err = -ENOMEM;
             goto err_out;
         }
         targets = tmp;
 
         target = &targets[target_cnt];
         memset(target, 0, sizeof(*target));
 
         target->abs_ip = usdt_abs_ip;
         target->rel_ip = usdt_rel_ip;
         target->sema_off = usdt_sema_off;
 
         /* notes.args references strings from Elf itself, so they can
          * be referenced safely until elf_end() call
          */
         target->spec_str = note.args;
 
         err = parse_usdt_spec(&target->spec, &note, usdt_cookie);
         if (err)
             goto err_out;
 
         target_cnt++;
     }
 
     *out_targets = targets;
     *out_target_cnt = target_cnt;
     err = target_cnt;
 
 err_out:
     free(segs);
     free(vma_segs);
     if (err < 0)
         free(targets);
     return err;
 }
 
 struct bpf_link_usdt {
     struct bpf_link link;
 
     struct usdt_manager *usdt_man;
 
     size_t spec_cnt;
     int *spec_ids;
 
     size_t uprobe_cnt;
     struct {
         long abs_ip;
         struct bpf_link *link;
     } *uprobes;
 };
 
 static int bpf_link_usdt_detach(struct bpf_link *link)
 {
     struct bpf_link_usdt *usdt_link = container_of(link, struct bpf_link_usdt, link);
     struct usdt_manager *man = usdt_link->usdt_man;
     int i;
 
     for (i = 0; i < usdt_link->uprobe_cnt; i++) {
         /* detach underlying uprobe link */
         bpf_link__destroy(usdt_link->uprobes[i].link);
         /* there is no need to update specs map because it will be
          * unconditionally overwritten on subsequent USDT attaches,
          * but if BPF cookies are not used we need to remove entry
          * from ip_to_spec_id map, otherwise we'll run into false
          * conflicting IP errors
          */
         if (!man->has_bpf_cookie) {
             /* not much we can do about errors here */
             (void)bpf_map_delete_elem(bpf_map__fd(man->ip_to_spec_id_map),
                           &usdt_link->uprobes[i].abs_ip);
         }
     }
 
     /* try to return the list of previously used spec IDs to usdt_manager
      * for future reuse for subsequent USDT attaches
      */
     if (!man->free_spec_ids) {
         /* if there were no free spec IDs yet, just transfer our IDs */
         man->free_spec_ids = usdt_link->spec_ids;
         man->free_spec_cnt = usdt_link->spec_cnt;
         usdt_link->spec_ids = NULL;
     } else {
         /* otherwise concat IDs */
         size_t new_cnt = man->free_spec_cnt + usdt_link->spec_cnt;
         int *new_free_ids;
 
         new_free_ids = libbpf_reallocarray(man->free_spec_ids, new_cnt,
                            sizeof(*new_free_ids));
         /* If we couldn't resize free_spec_ids, we'll just leak
          * a bunch of free IDs; this is very unlikely to happen and if
          * system is so exhausted on memory, it's the least of user's
          * concerns, probably.
          * So just do our best here to return those IDs to usdt_manager.
          */
         if (new_free_ids) {
             memcpy(new_free_ids + man->free_spec_cnt, usdt_link->spec_ids,
                    usdt_link->spec_cnt * sizeof(*usdt_link->spec_ids));
             man->free_spec_ids = new_free_ids;
             man->free_spec_cnt = new_cnt;
         }
     }
 
     return 0;
 }
 
 static void bpf_link_usdt_dealloc(struct bpf_link *link)
 {
     struct bpf_link_usdt *usdt_link = container_of(link, struct bpf_link_usdt, link);
 
     free(usdt_link->spec_ids);
     free(usdt_link->uprobes);
     free(usdt_link);
 }
 
 static size_t specs_hash_fn(const void *key, void *ctx)
 {
     const char *s = key;
 
     return str_hash(s);
 }
 
 static bool specs_equal_fn(const void *key1, const void *key2, void *ctx)
 {
     const char *s1 = key1;
     const char *s2 = key2;
 
     return strcmp(s1, s2) == 0;
 }
 
 static int allocate_spec_id(struct usdt_manager *man, struct hashmap *specs_hash,
                 struct bpf_link_usdt *link, struct usdt_target *target,
                 int *spec_id, bool *is_new)
 {
     void *tmp;
     int err;
 
     /* check if we already allocated spec ID for this spec string */
     if (hashmap__find(specs_hash, target->spec_str, &tmp)) {
         *spec_id = (long)tmp;
         *is_new = false;
         return 0;
     }
 
     /* otherwise it's a new ID that needs to be set up in specs map and
      * returned back to usdt_manager when USDT link is detached
      */
     tmp = libbpf_reallocarray(link->spec_ids, link->spec_cnt + 1, sizeof(*link->spec_ids));
     if (!tmp)
         return -ENOMEM;
     link->spec_ids = tmp;
 
     /* get next free spec ID, giving preference to free list, if not empty */
     if (man->free_spec_cnt) {
         *spec_id = man->free_spec_ids[man->free_spec_cnt - 1];
 
         /* cache spec ID for current spec string for future lookups */
         err = hashmap__add(specs_hash, target->spec_str, (void *)(long)*spec_id);
         if (err)
              return err;
 
         man->free_spec_cnt--;
     } else {
         /* don't allocate spec ID bigger than what fits in specs map */
         if (man->next_free_spec_id >= bpf_map__max_entries(man->specs_map))
             return -E2BIG;
 
         *spec_id = man->next_free_spec_id;
 
         /* cache spec ID for current spec string for future lookups */
         err = hashmap__add(specs_hash, target->spec_str, (void *)(long)*spec_id);
         if (err)
              return err;
 
         man->next_free_spec_id++;
     }
 
     /* remember new spec ID in the link for later return back to free list on detach */
     link->spec_ids[link->spec_cnt] = *spec_id;
     link->spec_cnt++;
     *is_new = true;
     return 0;
 }
 
 struct bpf_link *usdt_manager_attach_usdt(struct usdt_manager *man, const struct bpf_program *prog,
                       pid_t pid, const char *path,
                       const char *usdt_provider, const char *usdt_name,
                       __u64 usdt_cookie)
 {
     int i, fd, err, spec_map_fd, ip_map_fd;
     LIBBPF_OPTS(bpf_uprobe_opts, opts);
     struct hashmap *specs_hash = NULL;
     struct bpf_link_usdt *link = NULL;
     struct usdt_target *targets = NULL;
     size_t target_cnt;
     Elf *elf;
 
     spec_map_fd = bpf_map__fd(man->specs_map);
     ip_map_fd = bpf_map__fd(man->ip_to_spec_id_map);
 
     /* TODO: perform path resolution similar to uprobe's */
     fd = open(path, O_RDONLY);
     if (fd < 0) {
         err = -errno;
         pr_warn("usdt: failed to open ELF binary '%s': %d\n", path, err);
         return libbpf_err_ptr(err);
     }
 
     elf = elf_begin(fd, ELF_C_READ_MMAP, NULL);
     if (!elf) {
         err = -EBADF;
         pr_warn("usdt: failed to parse ELF binary '%s': %s\n", path, elf_errmsg(-1));
         goto err_out;
     }
 
     err = sanity_check_usdt_elf(elf, path);
     if (err)
         goto err_out;
 
     /* normalize PID filter */
     if (pid < 0)
         pid = -1;
     else if (pid == 0)
         pid = getpid();
 
     /* discover USDT in given binary, optionally limiting
      * activations to a given PID, if pid > 0
      */
     err = collect_usdt_targets(man, elf, path, pid, usdt_provider, usdt_name,
                    usdt_cookie, &targets, &target_cnt);
     if (err <= 0) {
         err = (err == 0) ? -ENOENT : err;
         goto err_out;
     }
 
     specs_hash = hashmap__new(specs_hash_fn, specs_equal_fn, NULL);
     if (IS_ERR(specs_hash)) {
         err = PTR_ERR(specs_hash);
         goto err_out;
     }
 
     link = calloc(1, sizeof(*link));
     if (!link) {
         err = -ENOMEM;
         goto err_out;
     }
 
     link->usdt_man = man;
     link->link.detach = &bpf_link_usdt_detach;
     link->link.dealloc = &bpf_link_usdt_dealloc;
 
     link->uprobes = calloc(target_cnt, sizeof(*link->uprobes));
     if (!link->uprobes) {
         err = -ENOMEM;
         goto err_out;
     }
 
     for (i = 0; i < target_cnt; i++) {
         struct usdt_target *target = &targets[i];
         struct bpf_link *uprobe_link;
         bool is_new;
         int spec_id;
 
         /* Spec ID can be either reused or newly allocated. If it is
          * newly allocated, we'll need to fill out spec map, otherwise
          * entire spec should be valid and can be just used by a new
          * uprobe. We reuse spec when USDT arg spec is identical. We
          * also never share specs between two different USDT
          * attachments ("links"), so all the reused specs already
          * share USDT cookie value implicitly.
          */
         err = allocate_spec_id(man, specs_hash, link, target, &spec_id, &is_new);
         if (err)
             goto err_out;
 
         if (is_new && bpf_map_update_elem(spec_map_fd, &spec_id, &target->spec, BPF_ANY)) {
             err = -errno;
             pr_warn("usdt: failed to set USDT spec #%d for '%s:%s' in '%s': %d\n",
                 spec_id, usdt_provider, usdt_name, path, err);
             goto err_out;
         }
         if (!man->has_bpf_cookie &&
             bpf_map_update_elem(ip_map_fd, &target->abs_ip, &spec_id, BPF_NOEXIST)) {
             err = -errno;
             if (err == -EEXIST) {
                 pr_warn("usdt: IP collision detected for spec #%d for '%s:%s' in '%s'\n",
                         spec_id, usdt_provider, usdt_name, path);
             } else {
                 pr_warn("usdt: failed to map IP 0x%lx to spec #%d for '%s:%s' in '%s': %d\n",
                     target->abs_ip, spec_id, usdt_provider, usdt_name,
                     path, err);
             }
             goto err_out;
         }
 
         opts.ref_ctr_offset = target->sema_off;
         opts.bpf_cookie = man->has_bpf_cookie ? spec_id : 0;
         uprobe_link = bpf_program__attach_uprobe_opts(prog, pid, path,
                                   target->rel_ip, &opts);
         err = libbpf_get_error(uprobe_link);
         if (err) {
             pr_warn("usdt: failed to attach uprobe #%d for '%s:%s' in '%s': %d\n",
                 i, usdt_provider, usdt_name, path, err);
             goto err_out;
         }
 
         link->uprobes[i].link = uprobe_link;
         link->uprobes[i].abs_ip = target->abs_ip;
         link->uprobe_cnt++;
     }
 
     free(targets);
     hashmap__free(specs_hash);
     elf_end(elf);
     close(fd);
 
     return &link->link;
 
 err_out:
     if (link)
         bpf_link__destroy(&link->link);
     free(targets);
     hashmap__free(specs_hash);
     if (elf)
         elf_end(elf);
     close(fd);
     return libbpf_err_ptr(err);
 }
 
 /* Parse out USDT ELF note from '.note.stapsdt' section.
  * Logic inspired by perf's code.
  */
 static int parse_usdt_note(Elf *elf, const char *path, GElf_Nhdr *nhdr,
                const char *data, size_t name_off, size_t desc_off,
                struct usdt_note *note)
 {
     const char *provider, *name, *args;
     long addrs[3];
     size_t len;
 
     /* sanity check USDT note name and type first */
     if (strncmp(data + name_off, USDT_NOTE_NAME, nhdr->n_namesz) != 0)
         return -EINVAL;
     if (nhdr->n_type != USDT_NOTE_TYPE)
         return -EINVAL;
 
     /* sanity check USDT note contents ("description" in ELF terminology) */
     len = nhdr->n_descsz;
     data = data + desc_off;
 
     /* +3 is the very minimum required to store three empty strings */
     if (len < sizeof(addrs) + 3)
         return -EINVAL;
 
     /* get location, base, and semaphore addrs */
     memcpy(&addrs, data, sizeof(addrs));
 
     /* parse string fields: provider, name, args */
     provider = data + sizeof(addrs);
 
     name = (const char *)memchr(provider, '\0', data + len - provider);
     if (!name) /* non-zero-terminated provider */
         return -EINVAL;
     name++;
     if (name >= data + len || *name == '\0') /* missing or empty name */
         return -EINVAL;
 
     args = memchr(name, '\0', data + len - name);
     if (!args) /* non-zero-terminated name */
         return -EINVAL;
     ++args;
     if (args >= data + len) /* missing arguments spec */
         return -EINVAL;
 
     note->provider = provider;
     note->name = name;
     if (*args == '\0' || *args == ':')
         note->args = "";
     else
         note->args = args;
     note->loc_addr = addrs[0];
     note->base_addr = addrs[1];
     note->sema_addr = addrs[2];
 
     return 0;
 }
 
 static int parse_usdt_arg(const char *arg_str, int arg_num, struct usdt_arg_spec *arg);
 
 static int parse_usdt_spec(struct usdt_spec *spec, const struct usdt_note *note, __u64 usdt_cookie)
 {
     const char *s;
     int len;
 
     spec->usdt_cookie = usdt_cookie;
     spec->arg_cnt = 0;
 
     s = note->args;
     while (s[0]) {
         if (spec->arg_cnt >= USDT_MAX_ARG_CNT) {
             pr_warn("usdt: too many USDT arguments (> %d) for '%s:%s' with args spec '%s'\n",
                 USDT_MAX_ARG_CNT, note->provider, note->name, note->args);
             return -E2BIG;
         }
 
         len = parse_usdt_arg(s, spec->arg_cnt, &spec->args[spec->arg_cnt]);
         if (len < 0)
             return len;
 
         s += len;
         spec->arg_cnt++;
     }
 
     return 0;
 }
 
 /* Architecture-specific logic for parsing USDT argument location specs */
 
 #if defined(__x86_64__) || defined(__i386__)
 
 static int calc_pt_regs_off(const char *reg_name)
 {
     static struct {
         const char *names[4];
         size_t pt_regs_off;
     } reg_map[] = {
 #ifdef __x86_64__
 #define reg_off(reg64, reg32) offsetof(struct pt_regs, reg64)
 #else
 #define reg_off(reg64, reg32) offsetof(struct pt_regs, reg32)
 #endif
         { {"rip", "eip", "", ""}, reg_off(rip, eip) },
         { {"rax", "eax", "ax", "al"}, reg_off(rax, eax) },
         { {"rbx", "ebx", "bx", "bl"}, reg_off(rbx, ebx) },
         { {"rcx", "ecx", "cx", "cl"}, reg_off(rcx, ecx) },
         { {"rdx", "edx", "dx", "dl"}, reg_off(rdx, edx) },
         { {"rsi", "esi", "si", "sil"}, reg_off(rsi, esi) },
         { {"rdi", "edi", "di", "dil"}, reg_off(rdi, edi) },
         { {"rbp", "ebp", "bp", "bpl"}, reg_off(rbp, ebp) },
         { {"rsp", "esp", "sp", "spl"}, reg_off(rsp, esp) },
 #undef reg_off
 #ifdef __x86_64__
         { {"r8", "r8d", "r8w", "r8b"}, offsetof(struct pt_regs, r8) },
         { {"r9", "r9d", "r9w", "r9b"}, offsetof(struct pt_regs, r9) },
         { {"r10", "r10d", "r10w", "r10b"}, offsetof(struct pt_regs, r10) },
         { {"r11", "r11d", "r11w", "r11b"}, offsetof(struct pt_regs, r11) },
         { {"r12", "r12d", "r12w", "r12b"}, offsetof(struct pt_regs, r12) },
         { {"r13", "r13d", "r13w", "r13b"}, offsetof(struct pt_regs, r13) },
         { {"r14", "r14d", "r14w", "r14b"}, offsetof(struct pt_regs, r14) },
         { {"r15", "r15d", "r15w", "r15b"}, offsetof(struct pt_regs, r15) },
 #endif
     };
     int i, j;
 
     for (i = 0; i < ARRAY_SIZE(reg_map); i++) {
         for (j = 0; j < ARRAY_SIZE(reg_map[i].names); j++) {
             if (strcmp(reg_name, reg_map[i].names[j]) == 0)
                 return reg_map[i].pt_regs_off;
         }
     }
 
     pr_warn("usdt: unrecognized register '%s'\n", reg_name);
     return -ENOENT;
 }
 
 static int parse_usdt_arg(const char *arg_str, int arg_num, struct usdt_arg_spec *arg)
 {
     char *reg_name = NULL;
     int arg_sz, len, reg_off;
     long off;
 
     if (sscanf(arg_str, " %d @ %ld ( %%%m[^)] ) %n", &arg_sz, &off, &reg_name, &len) == 3) {
         /* Memory dereference case, e.g., -4@-20(%rbp) */
         arg->arg_type = USDT_ARG_REG_DEREF;
         arg->val_off = off;
         reg_off = calc_pt_regs_off(reg_name);
         free(reg_name);
         if (reg_off < 0)
             return reg_off;
         arg->reg_off = reg_off;
     } else if (sscanf(arg_str, " %d @ %%%ms %n", &arg_sz, &reg_name, &len) == 2) {
         /* Register read case, e.g., -4@%eax */
         arg->arg_type = USDT_ARG_REG;
         arg->val_off = 0;
 
         reg_off = calc_pt_regs_off(reg_name);
         free(reg_name);
         if (reg_off < 0)
             return reg_off;
         arg->reg_off = reg_off;
     } else if (sscanf(arg_str, " %d @ $%ld %n", &arg_sz, &off, &len) == 2) {
         /* Constant value case, e.g., 4@$71 */
         arg->arg_type = USDT_ARG_CONST;
         arg->val_off = off;
         arg->reg_off = 0;
     } else {
         pr_warn("usdt: unrecognized arg #%d spec '%s'\n", arg_num, arg_str);
         return -EINVAL;
     }
 
     arg->arg_signed = arg_sz < 0;
     if (arg_sz < 0)
         arg_sz = -arg_sz;
 
     switch (arg_sz) {
     case 1: case 2: case 4: case 8:
         arg->arg_bitshift = 64 - arg_sz * 8;
         break;
     default:
         pr_warn("usdt: unsupported arg #%d (spec '%s') size: %d\n",
             arg_num, arg_str, arg_sz);
         return -EINVAL;
     }
 
     return len;
 }
 
 #elif defined(__s390x__)
 
 /* Do not support __s390__ for now, since user_pt_regs is broken with -m31. */
 
 static int parse_usdt_arg(const char *arg_str, int arg_num, struct usdt_arg_spec *arg)
 {
     unsigned int reg;
     int arg_sz, len;
     long off;
 
     if (sscanf(arg_str, " %d @ %ld ( %%r%u ) %n", &arg_sz, &off, &reg, &len) == 3) {
         /* Memory dereference case, e.g., -2@-28(%r15) */
         arg->arg_type = USDT_ARG_REG_DEREF;
         arg->val_off = off;
         if (reg > 15) {
             pr_warn("usdt: unrecognized register '%%r%u'\n", reg);
             return -EINVAL;
         }
         arg->reg_off = offsetof(user_pt_regs, gprs[reg]);
     } else if (sscanf(arg_str, " %d @ %%r%u %n", &arg_sz, &reg, &len) == 2) {
         /* Register read case, e.g., -8@%r0 */
         arg->arg_type = USDT_ARG_REG;
         arg->val_off = 0;
         if (reg > 15) {
             pr_warn("usdt: unrecognized register '%%r%u'\n", reg);
             return -EINVAL;
         }
         arg->reg_off = offsetof(user_pt_regs, gprs[reg]);
     } else if (sscanf(arg_str, " %d @ %ld %n", &arg_sz, &off, &len) == 2) {
         /* Constant value case, e.g., 4@71 */
         arg->arg_type = USDT_ARG_CONST;
         arg->val_off = off;
         arg->reg_off = 0;
     } else {
         pr_warn("usdt: unrecognized arg #%d spec '%s'\n", arg_num, arg_str);
         return -EINVAL;
     }
 
     arg->arg_signed = arg_sz < 0;
     if (arg_sz < 0)
         arg_sz = -arg_sz;
 
     switch (arg_sz) {
     case 1: case 2: case 4: case 8:
         arg->arg_bitshift = 64 - arg_sz * 8;
         break;
     default:
         pr_warn("usdt: unsupported arg #%d (spec '%s') size: %d\n",
             arg_num, arg_str, arg_sz);
         return -EINVAL;
     }
 
     return len;
 }
 
 #elif defined(__aarch64__)
 
 static int calc_pt_regs_off(const char *reg_name)
 {
     int reg_num;
 
     if (sscanf(reg_name, "x%d", &reg_num) == 1) {
         if (reg_num >= 0 && reg_num < 31)
             return offsetof(struct user_pt_regs, regs[reg_num]);
     } else if (strcmp(reg_name, "sp") == 0) {
         return offsetof(struct user_pt_regs, sp);
     }
     pr_warn("usdt: unrecognized register '%s'\n", reg_name);
     return -ENOENT;
 }
 
 static int parse_usdt_arg(const char *arg_str, int arg_num, struct usdt_arg_spec *arg)
 {
     char *reg_name = NULL;
     int arg_sz, len, reg_off;
     long off;
 
     if (sscanf(arg_str, " %d @ \[ %m[a-z0-9], %ld ] %n", &arg_sz, &reg_name, &off, &len) == 3) {
         /* Memory dereference case, e.g., -4@[sp, 96] */
         arg->arg_type = USDT_ARG_REG_DEREF;
         arg->val_off = off;
         reg_off = calc_pt_regs_off(reg_name);
         free(reg_name);
         if (reg_off < 0)
             return reg_off;
         arg->reg_off = reg_off;
     } else if (sscanf(arg_str, " %d @ \[ %m[a-z0-9] ] %n", &arg_sz, &reg_name, &len) == 2) {
         /* Memory dereference case, e.g., -4@[sp] */
         arg->arg_type = USDT_ARG_REG_DEREF;
         arg->val_off = 0;
         reg_off = calc_pt_regs_off(reg_name);
         free(reg_name);
         if (reg_off < 0)
             return reg_off;
         arg->reg_off = reg_off;
     } else if (sscanf(arg_str, " %d @ %ld %n", &arg_sz, &off, &len) == 2) {
         /* Constant value case, e.g., 4@5 */
         arg->arg_type = USDT_ARG_CONST;
         arg->val_off = off;
         arg->reg_off = 0;
     } else if (sscanf(arg_str, " %d @ %m[a-z0-9] %n", &arg_sz, &reg_name, &len) == 2) {
         /* Register read case, e.g., -8@x4 */
         arg->arg_type = USDT_ARG_REG;
         arg->val_off = 0;
         reg_off = calc_pt_regs_off(reg_name);
         free(reg_name);
         if (reg_off < 0)
             return reg_off;
         arg->reg_off = reg_off;
     } else {
         pr_warn("usdt: unrecognized arg #%d spec '%s'\n", arg_num, arg_str);
         return -EINVAL;
     }
 
     arg->arg_signed = arg_sz < 0;
     if (arg_sz < 0)
         arg_sz = -arg_sz;
 
     switch (arg_sz) {
     case 1: case 2: case 4: case 8:
         arg->arg_bitshift = 64 - arg_sz * 8;
         break;
     default:
         pr_warn("usdt: unsupported arg #%d (spec '%s') size: %d\n",
             arg_num, arg_str, arg_sz);
         return -EINVAL;
     }
 
     return len;
 }
 
 #elif defined(__riscv)
 
 static int calc_pt_regs_off(const char *reg_name)
 {
     static struct {
         const char *name;
         size_t pt_regs_off;
     } reg_map[] = {
         { "ra", offsetof(struct user_regs_struct, ra) },
         { "sp", offsetof(struct user_regs_struct, sp) },
         { "gp", offsetof(struct user_regs_struct, gp) },
         { "tp", offsetof(struct user_regs_struct, tp) },
         { "a0", offsetof(struct user_regs_struct, a0) },
         { "a1", offsetof(struct user_regs_struct, a1) },
         { "a2", offsetof(struct user_regs_struct, a2) },
         { "a3", offsetof(struct user_regs_struct, a3) },
         { "a4", offsetof(struct user_regs_struct, a4) },
         { "a5", offsetof(struct user_regs_struct, a5) },
         { "a6", offsetof(struct user_regs_struct, a6) },
         { "a7", offsetof(struct user_regs_struct, a7) },
         { "s0", offsetof(struct user_regs_struct, s0) },
         { "s1", offsetof(struct user_regs_struct, s1) },
         { "s2", offsetof(struct user_regs_struct, s2) },
         { "s3", offsetof(struct user_regs_struct, s3) },
         { "s4", offsetof(struct user_regs_struct, s4) },
         { "s5", offsetof(struct user_regs_struct, s5) },
         { "s6", offsetof(struct user_regs_struct, s6) },
         { "s7", offsetof(struct user_regs_struct, s7) },
         { "s8", offsetof(struct user_regs_struct, rv_s8) },
         { "s9", offsetof(struct user_regs_struct, s9) },
         { "s10", offsetof(struct user_regs_struct, s10) },
         { "s11", offsetof(struct user_regs_struct, s11) },
         { "t0", offsetof(struct user_regs_struct, t0) },
         { "t1", offsetof(struct user_regs_struct, t1) },
         { "t2", offsetof(struct user_regs_struct, t2) },
         { "t3", offsetof(struct user_regs_struct, t3) },
         { "t4", offsetof(struct user_regs_struct, t4) },
         { "t5", offsetof(struct user_regs_struct, t5) },
         { "t6", offsetof(struct user_regs_struct, t6) },
     };
     int i;
 
     for (i = 0; i < ARRAY_SIZE(reg_map); i++) {
         if (strcmp(reg_name, reg_map[i].name) == 0)
             return reg_map[i].pt_regs_off;
     }
 
     pr_warn("usdt: unrecognized register '%s'\n", reg_name);
     return -ENOENT;
 }
 
 static int parse_usdt_arg(const char *arg_str, int arg_num, struct usdt_arg_spec *arg)
 {
     char *reg_name = NULL;
     int arg_sz, len, reg_off;
     long off;
 
     if (sscanf(arg_str, " %d @ %ld ( %m[a-z0-9] ) %n", &arg_sz, &off, &reg_name, &len) == 3) {
         /* Memory dereference case, e.g., -8@-88(s0) */
         arg->arg_type = USDT_ARG_REG_DEREF;
         arg->val_off = off;
         reg_off = calc_pt_regs_off(reg_name);
         free(reg_name);
         if (reg_off < 0)
             return reg_off;
         arg->reg_off = reg_off;
     } else if (sscanf(arg_str, " %d @ %ld %n", &arg_sz, &off, &len) == 2) {
         /* Constant value case, e.g., 4@5 */
         arg->arg_type = USDT_ARG_CONST;
         arg->val_off = off;
         arg->reg_off = 0;
     } else if (sscanf(arg_str, " %d @ %m[a-z0-9] %n", &arg_sz, &reg_name, &len) == 2) {
         /* Register read case, e.g., -8@a1 */
         arg->arg_type = USDT_ARG_REG;
         arg->val_off = 0;
         reg_off = calc_pt_regs_off(reg_name);
         free(reg_name);
         if (reg_off < 0)
             return reg_off;
         arg->reg_off = reg_off;
     } else {
         pr_warn("usdt: unrecognized arg #%d spec '%s'\n", arg_num, arg_str);
         return -EINVAL;
     }
 
     arg->arg_signed = arg_sz < 0;
     if (arg_sz < 0)
         arg_sz = -arg_sz;
 
     switch (arg_sz) {
     case 1: case 2: case 4: case 8:
         arg->arg_bitshift = 64 - arg_sz * 8;
         break;
     default:
         pr_warn("usdt: unsupported arg #%d (spec '%s') size: %d\n",
             arg_num, arg_str, arg_sz);
         return -EINVAL;
     }
 
     return len;
 }
 
 #else
 
 static int parse_usdt_arg(const char *arg_str, int arg_num, struct usdt_arg_spec *arg)
 {
     pr_warn("usdt: libbpf doesn't support USDTs on current architecture\n");
     return -ENOTSUP;
 }
 
 #endif

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