1/* SPDX-License-Identifier: GPL-2.0 */
2/*
3 * Non-emulated single-stepping support (currently limited to basic integer
4 * computations) used to validate the instruction emulation infrastructure.
5 *
6 * Copyright (C) 2019 IBM Corporation
7 */
8
9#include <asm/asm-offsets.h>
10#include <asm/ppc_asm.h>
11#include <asm/code-patching-asm.h>
12#include <linux/errno.h>
13
14/* int exec_instr(struct pt_regs *regs) */
15_GLOBAL(exec_instr)
16
17 /*
18 * Stack frame layout (INT_FRAME_SIZE bytes)
19 * In-memory pt_regs (SP + STACK_INT_FRAME_REGS)
20 * Scratch space (SP + 8)
21 * Back chain (SP + 0)
22 */
23
24 /*
25 * Allocate a new stack frame with enough space to hold the register
26 * states in an in-memory pt_regs and also create the back chain to
27 * the caller's stack frame.
28 */
29 stdu r1, -INT_FRAME_SIZE(r1)
30
31 /*
32 * Save non-volatile GPRs on stack. This includes TOC pointer (GPR2)
33 * and local variables (GPR14 to GPR31). The register for the pt_regs
34 * parameter (GPR3) is saved additionally to ensure that the resulting
35 * register state can still be saved even if GPR3 gets overwritten
36 * when loading the initial register state for the test instruction.
37 * The stack pointer (GPR1) and the thread pointer (GPR13) are not
38 * saved as these should not be modified anyway.
39 */
40 SAVE_GPRS(2, 3, r1)
41 SAVE_NVGPRS(r1)
42
43 /*
44 * Save LR on stack to ensure that the return address is available
45 * even if it gets overwritten by the test instruction.
46 */
47 mflr r0
48 std r0, _LINK(r1)
49
50 /*
51 * Save CR on stack. For simplicity, the entire register is saved
52 * even though only fields 2 to 4 are non-volatile.
53 */
54 mfcr r0
55 std r0, _CCR(r1)
56
57 /*
58 * Load register state for the test instruction without touching the
59 * critical non-volatile registers. The register state is passed as a
60 * pointer to a pt_regs instance.
61 */
62 subi r31, r3, GPR0
63
64 /* Load LR from pt_regs */
65 ld r0, _LINK(r31)
66 mtlr r0
67
68 /* Load CR from pt_regs */
69 ld r0, _CCR(r31)
70 mtcr r0
71
72 /* Load XER from pt_regs */
73 ld r0, _XER(r31)
74 mtxer r0
75
76 /* Load GPRs from pt_regs */
77 REST_GPR(0, r31)
78 REST_GPRS(2, 12, r31)
79 REST_NVGPRS(r31)
80
81 /* Placeholder for the test instruction */
82 .balign 64
831: nop
84 nop
85 patch_site 1b patch__exec_instr
86
87 /*
88 * Since GPR3 is overwritten, temporarily restore it back to its
89 * original state, i.e. the pointer to pt_regs, to ensure that the
90 * resulting register state can be saved. Before doing this, a copy
91 * of it is created in the scratch space which is used later on to
92 * save it to pt_regs.
93 */
94 std r3, 8(r1)
95 REST_GPR(3, r1)
96
97 /* Save resulting GPR state to pt_regs */
98 subi r3, r3, GPR0
99 SAVE_GPR(0, r3)
100 SAVE_GPR(2, r3)
101 SAVE_GPRS(4, 12, r3)
102 SAVE_NVGPRS(r3)
103
104 /* Save resulting LR to pt_regs */
105 mflr r0
106 std r0, _LINK(r3)
107
108 /* Save resulting CR to pt_regs */
109 mfcr r0
110 std r0, _CCR(r3)
111
112 /* Save resulting XER to pt_regs */
113 mfxer r0
114 std r0, _XER(r3)
115
116 /* Restore resulting GPR3 from scratch space and save it to pt_regs */
117 ld r0, 8(r1)
118 std r0, GPR3(r3)
119
120 /* Set return value to denote execution success */
121 li r3, 0
122
123 /* Continue */
124 b 3f
125
126 /* Set return value to denote execution failure */
1272: li r3, -EFAULT
128
129 /* Restore the non-volatile GPRs from stack */
1303: REST_GPR(2, r1)
131 REST_NVGPRS(r1)
132
133 /* Restore LR from stack to be able to return */
134 ld r0, _LINK(r1)
135 mtlr r0
136
137 /* Restore CR from stack */
138 ld r0, _CCR(r1)
139 mtcr r0
140
141 /* Tear down stack frame */
142 addi r1, r1, INT_FRAME_SIZE
143
144 /* Return */
145 blr
146
147 /* Setup exception table */
148 EX_TABLE(1b, 2b)
149
150_ASM_NOKPROBE_SYMBOL(exec_instr)
151

source code of linux/arch/powerpc/lib/test_emulate_step_exec_instr.S