Linux kernel mirror (for testing)
git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git
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linux
1/*
2 * Single-step support.
3 *
4 * Copyright (C) 2004 Paul Mackerras <paulus@au.ibm.com>, IBM
5 *
6 * This program is free software; you can redistribute it and/or
7 * modify it under the terms of the GNU General Public License
8 * as published by the Free Software Foundation; either version
9 * 2 of the License, or (at your option) any later version.
10 */
11#include <linux/kernel.h>
12#include <linux/ptrace.h>
13#include <asm/sstep.h>
14#include <asm/processor.h>
15
16extern char system_call_common[];
17
18/* Bits in SRR1 that are copied from MSR */
19#define MSR_MASK 0xffffffff87c0ffff
20
21/*
22 * Determine whether a conditional branch instruction would branch.
23 */
24static int branch_taken(unsigned int instr, struct pt_regs *regs)
25{
26 unsigned int bo = (instr >> 21) & 0x1f;
27 unsigned int bi;
28
29 if ((bo & 4) == 0) {
30 /* decrement counter */
31 --regs->ctr;
32 if (((bo >> 1) & 1) ^ (regs->ctr == 0))
33 return 0;
34 }
35 if ((bo & 0x10) == 0) {
36 /* check bit from CR */
37 bi = (instr >> 16) & 0x1f;
38 if (((regs->ccr >> (31 - bi)) & 1) != ((bo >> 3) & 1))
39 return 0;
40 }
41 return 1;
42}
43
44/*
45 * Emulate instructions that cause a transfer of control.
46 * Returns 1 if the step was emulated, 0 if not,
47 * or -1 if the instruction is one that should not be stepped,
48 * such as an rfid, or a mtmsrd that would clear MSR_RI.
49 */
50int emulate_step(struct pt_regs *regs, unsigned int instr)
51{
52 unsigned int opcode, rd;
53 unsigned long int imm;
54
55 opcode = instr >> 26;
56 switch (opcode) {
57 case 16: /* bc */
58 imm = (signed short)(instr & 0xfffc);
59 if ((instr & 2) == 0)
60 imm += regs->nip;
61 regs->nip += 4;
62 if ((regs->msr & MSR_SF) == 0)
63 regs->nip &= 0xffffffffUL;
64 if (instr & 1)
65 regs->link = regs->nip;
66 if (branch_taken(instr, regs))
67 regs->nip = imm;
68 return 1;
69 case 17: /* sc */
70 /*
71 * N.B. this uses knowledge about how the syscall
72 * entry code works. If that is changed, this will
73 * need to be changed also.
74 */
75 regs->gpr[9] = regs->gpr[13];
76 regs->gpr[11] = regs->nip + 4;
77 regs->gpr[12] = regs->msr & MSR_MASK;
78 regs->gpr[13] = (unsigned long) get_paca();
79 regs->nip = (unsigned long) &system_call_common;
80 regs->msr = MSR_KERNEL;
81 return 1;
82 case 18: /* b */
83 imm = instr & 0x03fffffc;
84 if (imm & 0x02000000)
85 imm -= 0x04000000;
86 if ((instr & 2) == 0)
87 imm += regs->nip;
88 if (instr & 1) {
89 regs->link = regs->nip + 4;
90 if ((regs->msr & MSR_SF) == 0)
91 regs->link &= 0xffffffffUL;
92 }
93 if ((regs->msr & MSR_SF) == 0)
94 imm &= 0xffffffffUL;
95 regs->nip = imm;
96 return 1;
97 case 19:
98 switch (instr & 0x7fe) {
99 case 0x20: /* bclr */
100 case 0x420: /* bcctr */
101 imm = (instr & 0x400)? regs->ctr: regs->link;
102 regs->nip += 4;
103 if ((regs->msr & MSR_SF) == 0) {
104 regs->nip &= 0xffffffffUL;
105 imm &= 0xffffffffUL;
106 }
107 if (instr & 1)
108 regs->link = regs->nip;
109 if (branch_taken(instr, regs))
110 regs->nip = imm;
111 return 1;
112 case 0x24: /* rfid, scary */
113 return -1;
114 }
115 case 31:
116 rd = (instr >> 21) & 0x1f;
117 switch (instr & 0x7fe) {
118 case 0xa6: /* mfmsr */
119 regs->gpr[rd] = regs->msr & MSR_MASK;
120 regs->nip += 4;
121 if ((regs->msr & MSR_SF) == 0)
122 regs->nip &= 0xffffffffUL;
123 return 1;
124 case 0x164: /* mtmsrd */
125 /* only MSR_EE and MSR_RI get changed if bit 15 set */
126 /* mtmsrd doesn't change MSR_HV and MSR_ME */
127 imm = (instr & 0x10000)? 0x8002: 0xefffffffffffefffUL;
128 imm = (regs->msr & MSR_MASK & ~imm)
129 | (regs->gpr[rd] & imm);
130 if ((imm & MSR_RI) == 0)
131 /* can't step mtmsrd that would clear MSR_RI */
132 return -1;
133 regs->msr = imm;
134 regs->nip += 4;
135 if ((imm & MSR_SF) == 0)
136 regs->nip &= 0xffffffffUL;
137 return 1;
138 }
139 }
140 return 0;
141}