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/* SPDX-License-Identifier: GPL-2.0 */
/*
* Non-emulated single-stepping support (currently limited to basic integer
* computations) used to validate the instruction emulation infrastructure.
*
* Copyright (C) 2019 IBM Corporation
*/
#include <asm/asm-offsets.h>
#include <asm/ppc_asm.h>
#include <asm/code-patching-asm.h>
#include <linux/errno.h>
/* int exec_instr(struct pt_regs *regs) */
_GLOBAL(exec_instr)
/*
* Stack frame layout (INT_FRAME_SIZE bytes)
* In-memory pt_regs (SP + STACK_FRAME_OVERHEAD)
* Scratch space (SP + 8)
* Back chain (SP + 0)
*/
/*
* Allocate a new stack frame with enough space to hold the register
* states in an in-memory pt_regs and also create the back chain to
* the caller's stack frame.
*/
stdu r1, -INT_FRAME_SIZE(r1)
/*
* Save non-volatile GPRs on stack. This includes TOC pointer (GPR2)
* and local variables (GPR14 to GPR31). The register for the pt_regs
* parameter (GPR3) is saved additionally to ensure that the resulting
* register state can still be saved even if GPR3 gets overwritten
* when loading the initial register state for the test instruction.
* The stack pointer (GPR1) and the thread pointer (GPR13) are not
* saved as these should not be modified anyway.
*/
SAVE_2GPRS(2, r1)
SAVE_NVGPRS(r1)
/*
* Save LR on stack to ensure that the return address is available
* even if it gets overwritten by the test instruction.
*/
mflr r0
std r0, _LINK(r1)
/*
* Save CR on stack. For simplicity, the entire register is saved
* even though only fields 2 to 4 are non-volatile.
*/
mfcr r0
std r0, _CCR(r1)
/*
* Load register state for the test instruction without touching the
* critical non-volatile registers. The register state is passed as a
* pointer to a pt_regs instance.
*/
subi r31, r3, GPR0
/* Load LR from pt_regs */
ld r0, _LINK(r31)
mtlr r0
/* Load CR from pt_regs */
ld r0, _CCR(r31)
mtcr r0
/* Load XER from pt_regs */
ld r0, _XER(r31)
mtxer r0
/* Load GPRs from pt_regs */
REST_GPR(0, r31)
REST_10GPRS(2, r31)
REST_GPR(12, r31)
REST_NVGPRS(r31)
/* Placeholder for the test instruction */
1: nop
patch_site 1b patch__exec_instr
/*
* Since GPR3 is overwritten, temporarily restore it back to its
* original state, i.e. the pointer to pt_regs, to ensure that the
* resulting register state can be saved. Before doing this, a copy
* of it is created in the scratch space which is used later on to
* save it to pt_regs.
*/
std r3, 8(r1)
REST_GPR(3, r1)
/* Save resulting GPR state to pt_regs */
subi r3, r3, GPR0
SAVE_GPR(0, r3)
SAVE_GPR(2, r3)
SAVE_8GPRS(4, r3)
SAVE_GPR(12, r3)
SAVE_NVGPRS(r3)
/* Save resulting LR to pt_regs */
mflr r0
std r0, _LINK(r3)
/* Save resulting CR to pt_regs */
mfcr r0
std r0, _CCR(r3)
/* Save resulting XER to pt_regs */
mfxer r0
std r0, _XER(r3)
/* Restore resulting GPR3 from scratch space and save it to pt_regs */
ld r0, 8(r1)
std r0, GPR3(r3)
/* Set return value to denote execution success */
li r3, 0
/* Continue */
b 3f
/* Set return value to denote execution failure */
2: li r3, -EFAULT
/* Restore the non-volatile GPRs from stack */
3: REST_GPR(2, r1)
REST_NVGPRS(r1)
/* Restore LR from stack to be able to return */
ld r0, _LINK(r1)
mtlr r0
/* Restore CR from stack */
ld r0, _CCR(r1)
mtcr r0
/* Tear down stack frame */
addi r1, r1, INT_FRAME_SIZE
/* Return */
blr
/* Setup exception table */
EX_TABLE(1b, 2b)
_ASM_NOKPROBE_SYMBOL(exec_instr)
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