powerpc/lib/test_emulate_step_exec_instr.S

0001 /* SPDX-License-Identifier: GPL-2.0 */
0002 /*
0003  * Non-emulated single-stepping support (currently limited to basic integer
0004  * computations) used to validate the instruction emulation infrastructure.
0005  *
0006  * Copyright (C) 2019 IBM Corporation
0007  */
0008
0009 #include <asm/asm-offsets.h>
0010 #include <asm/ppc_asm.h>
0011 #include <asm/code-patching-asm.h>
0012 #include <linux/errno.h>
0013
0014 /* int exec_instr(struct pt_regs *regs) */
0015 _GLOBAL(exec_instr)
0016
0017     /*
0018      * Stack frame layout (INT_FRAME_SIZE bytes)
0019      *   In-memory pt_regs  (SP + STACK_FRAME_OVERHEAD)
0020      *   Scratch space  (SP + 8)
0021      *   Back chain     (SP + 0)
0022      */
0023
0024     /*
0025      * Allocate a new stack frame with enough space to hold the register
0026      * states in an in-memory pt_regs and also create the back chain to
0027      * the caller's stack frame.
0028      */
0029     stdu    r1, -INT_FRAME_SIZE(r1)
0030
0031     /*
0032      * Save non-volatile GPRs on stack. This includes TOC pointer (GPR2)
0033      * and local variables (GPR14 to GPR31). The register for the pt_regs
0034      * parameter (GPR3) is saved additionally to ensure that the resulting
0035      * register state can still be saved even if GPR3 gets overwritten
0036      * when loading the initial register state for the test instruction.
0037      * The stack pointer (GPR1) and the thread pointer (GPR13) are not
0038      * saved as these should not be modified anyway.
0039      */
0040     SAVE_GPRS(2, 3, r1)
0041     SAVE_NVGPRS(r1)
0042
0043     /*
0044      * Save LR on stack to ensure that the return address is available
0045      * even if it gets overwritten by the test instruction.
0046      */
0047     mflr    r0
0048     std r0, _LINK(r1)
0049
0050     /*
0051      * Save CR on stack. For simplicity, the entire register is saved
0052      * even though only fields 2 to 4 are non-volatile.
0053      */
0054     mfcr    r0
0055     std r0, _CCR(r1)
0056
0057     /*
0058      * Load register state for the test instruction without touching the
0059      * critical non-volatile registers. The register state is passed as a
0060      * pointer to a pt_regs instance.
0061      */
0062     subi    r31, r3, GPR0
0063
0064     /* Load LR from pt_regs */
0065     ld  r0, _LINK(r31)
0066     mtlr    r0
0067
0068     /* Load CR from pt_regs */
0069     ld  r0, _CCR(r31)
0070     mtcr    r0
0071
0072     /* Load XER from pt_regs */
0073     ld  r0, _XER(r31)
0074     mtxer   r0
0075
0076     /* Load GPRs from pt_regs */
0077     REST_GPR(0, r31)
0078     REST_GPRS(2, 12, r31)
0079     REST_NVGPRS(r31)
0080
0081     /* Placeholder for the test instruction */
0082     .balign 64
0083 1:  nop
0084     nop
0085     patch_site 1b patch__exec_instr
0086
0087     /*
0088      * Since GPR3 is overwritten, temporarily restore it back to its
0089      * original state, i.e. the pointer to pt_regs, to ensure that the
0090      * resulting register state can be saved. Before doing this, a copy
0091      * of it is created in the scratch space which is used later on to
0092      * save it to pt_regs.
0093      */
0094     std r3, 8(r1)
0095     REST_GPR(3, r1)
0096
0097     /* Save resulting GPR state to pt_regs */
0098     subi    r3, r3, GPR0
0099     SAVE_GPR(0, r3)
0100     SAVE_GPR(2, r3)
0101     SAVE_GPRS(4, 12, r3)
0102     SAVE_NVGPRS(r3)
0103
0104     /* Save resulting LR to pt_regs */
0105     mflr    r0
0106     std r0, _LINK(r3)
0107
0108     /* Save resulting CR to pt_regs */
0109     mfcr    r0
0110     std r0, _CCR(r3)
0111
0112     /* Save resulting XER to pt_regs */
0113     mfxer   r0
0114     std r0, _XER(r3)
0115
0116     /* Restore resulting GPR3 from scratch space and save it to pt_regs */
0117     ld  r0, 8(r1)
0118     std r0, GPR3(r3)
0119
0120     /* Set return value to denote execution success */
0121     li  r3, 0
0122
0123     /* Continue */
0124     b   3f
0125
0126     /* Set return value to denote execution failure */
0127 2:  li  r3, -EFAULT
0128
0129     /* Restore the non-volatile GPRs from stack */
0130 3:  REST_GPR(2, r1)
0131     REST_NVGPRS(r1)
0132
0133     /* Restore LR from stack to be able to return */
0134     ld  r0, _LINK(r1)
0135     mtlr    r0
0136
0137     /* Restore CR from stack */
0138     ld  r0, _CCR(r1)
0139     mtcr    r0
0140
0141     /* Tear down stack frame */
0142     addi    r1, r1, INT_FRAME_SIZE
0143
0144     /* Return */
0145     blr
0146
0147     /* Setup exception table */
0148     EX_TABLE(1b, 2b)
0149
0150 _ASM_NOKPROBE_SYMBOL(exec_instr)