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Paul Mackerras14cf11a2005-09-26 16:04:21 +10001/*
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>
Gui,Jian0d69a052006-11-01 10:50:15 +080012#include <linux/kprobes.h>
Paul Mackerras14cf11a2005-09-26 16:04:21 +100013#include <linux/ptrace.h>
14#include <asm/sstep.h>
15#include <asm/processor.h>
16
17extern char system_call_common[];
18
Paul Mackerrasc0325242005-10-28 22:48:08 +100019#ifdef CONFIG_PPC64
Paul Mackerras14cf11a2005-09-26 16:04:21 +100020/* Bits in SRR1 that are copied from MSR */
Stephen Rothwellaf308372006-03-23 17:38:10 +110021#define MSR_MASK 0xffffffff87c0ffffUL
Paul Mackerrasc0325242005-10-28 22:48:08 +100022#else
23#define MSR_MASK 0x87c0ffff
24#endif
Paul Mackerras14cf11a2005-09-26 16:04:21 +100025
26/*
27 * Determine whether a conditional branch instruction would branch.
28 */
Gui,Jian0d69a052006-11-01 10:50:15 +080029static int __kprobes branch_taken(unsigned int instr, struct pt_regs *regs)
Paul Mackerras14cf11a2005-09-26 16:04:21 +100030{
31 unsigned int bo = (instr >> 21) & 0x1f;
32 unsigned int bi;
33
34 if ((bo & 4) == 0) {
35 /* decrement counter */
36 --regs->ctr;
37 if (((bo >> 1) & 1) ^ (regs->ctr == 0))
38 return 0;
39 }
40 if ((bo & 0x10) == 0) {
41 /* check bit from CR */
42 bi = (instr >> 16) & 0x1f;
43 if (((regs->ccr >> (31 - bi)) & 1) != ((bo >> 3) & 1))
44 return 0;
45 }
46 return 1;
47}
48
49/*
50 * Emulate instructions that cause a transfer of control.
51 * Returns 1 if the step was emulated, 0 if not,
52 * or -1 if the instruction is one that should not be stepped,
53 * such as an rfid, or a mtmsrd that would clear MSR_RI.
54 */
Gui,Jian0d69a052006-11-01 10:50:15 +080055int __kprobes emulate_step(struct pt_regs *regs, unsigned int instr)
Paul Mackerras14cf11a2005-09-26 16:04:21 +100056{
Ananth N Mavinakayanahalli68881992007-04-18 15:56:38 +100057 unsigned int opcode, rs, rb, rd, spr;
Paul Mackerras14cf11a2005-09-26 16:04:21 +100058 unsigned long int imm;
59
60 opcode = instr >> 26;
61 switch (opcode) {
62 case 16: /* bc */
63 imm = (signed short)(instr & 0xfffc);
64 if ((instr & 2) == 0)
65 imm += regs->nip;
66 regs->nip += 4;
67 if ((regs->msr & MSR_SF) == 0)
68 regs->nip &= 0xffffffffUL;
69 if (instr & 1)
70 regs->link = regs->nip;
71 if (branch_taken(instr, regs))
72 regs->nip = imm;
73 return 1;
Paul Mackerrasc0325242005-10-28 22:48:08 +100074#ifdef CONFIG_PPC64
Paul Mackerras14cf11a2005-09-26 16:04:21 +100075 case 17: /* sc */
76 /*
77 * N.B. this uses knowledge about how the syscall
78 * entry code works. If that is changed, this will
79 * need to be changed also.
80 */
81 regs->gpr[9] = regs->gpr[13];
82 regs->gpr[11] = regs->nip + 4;
83 regs->gpr[12] = regs->msr & MSR_MASK;
84 regs->gpr[13] = (unsigned long) get_paca();
85 regs->nip = (unsigned long) &system_call_common;
86 regs->msr = MSR_KERNEL;
87 return 1;
Paul Mackerrasc0325242005-10-28 22:48:08 +100088#endif
Paul Mackerras14cf11a2005-09-26 16:04:21 +100089 case 18: /* b */
90 imm = instr & 0x03fffffc;
91 if (imm & 0x02000000)
92 imm -= 0x04000000;
93 if ((instr & 2) == 0)
94 imm += regs->nip;
95 if (instr & 1) {
96 regs->link = regs->nip + 4;
97 if ((regs->msr & MSR_SF) == 0)
98 regs->link &= 0xffffffffUL;
99 }
100 if ((regs->msr & MSR_SF) == 0)
101 imm &= 0xffffffffUL;
102 regs->nip = imm;
103 return 1;
104 case 19:
105 switch (instr & 0x7fe) {
106 case 0x20: /* bclr */
107 case 0x420: /* bcctr */
108 imm = (instr & 0x400)? regs->ctr: regs->link;
109 regs->nip += 4;
110 if ((regs->msr & MSR_SF) == 0) {
111 regs->nip &= 0xffffffffUL;
112 imm &= 0xffffffffUL;
113 }
114 if (instr & 1)
115 regs->link = regs->nip;
116 if (branch_taken(instr, regs))
117 regs->nip = imm;
118 return 1;
119 case 0x24: /* rfid, scary */
120 return -1;
121 }
122 case 31:
123 rd = (instr >> 21) & 0x1f;
124 switch (instr & 0x7fe) {
125 case 0xa6: /* mfmsr */
126 regs->gpr[rd] = regs->msr & MSR_MASK;
127 regs->nip += 4;
128 if ((regs->msr & MSR_SF) == 0)
129 regs->nip &= 0xffffffffUL;
130 return 1;
Paul Mackerrasc0325242005-10-28 22:48:08 +1000131 case 0x124: /* mtmsr */
132 imm = regs->gpr[rd];
133 if ((imm & MSR_RI) == 0)
134 /* can't step mtmsr that would clear MSR_RI */
135 return -1;
136 regs->msr = imm;
137 regs->nip += 4;
138 return 1;
139#ifdef CONFIG_PPC64
Paul Mackerras14cf11a2005-09-26 16:04:21 +1000140 case 0x164: /* mtmsrd */
141 /* only MSR_EE and MSR_RI get changed if bit 15 set */
142 /* mtmsrd doesn't change MSR_HV and MSR_ME */
143 imm = (instr & 0x10000)? 0x8002: 0xefffffffffffefffUL;
144 imm = (regs->msr & MSR_MASK & ~imm)
145 | (regs->gpr[rd] & imm);
146 if ((imm & MSR_RI) == 0)
147 /* can't step mtmsrd that would clear MSR_RI */
148 return -1;
149 regs->msr = imm;
150 regs->nip += 4;
151 if ((imm & MSR_SF) == 0)
152 regs->nip &= 0xffffffffUL;
153 return 1;
Paul Mackerrasc0325242005-10-28 22:48:08 +1000154#endif
Ananth N Mavinakayanahalli68881992007-04-18 15:56:38 +1000155 case 0x26: /* mfcr */
156 regs->gpr[rd] = regs->ccr;
157 regs->gpr[rd] &= 0xffffffffUL;
158 goto mtspr_out;
159 case 0x2a6: /* mfspr */
160 spr = (instr >> 11) & 0x3ff;
161 switch (spr) {
162 case 0x20: /* mfxer */
163 regs->gpr[rd] = regs->xer;
164 regs->gpr[rd] &= 0xffffffffUL;
165 goto mtspr_out;
166 case 0x100: /* mflr */
167 regs->gpr[rd] = regs->link;
168 goto mtspr_out;
169 case 0x120: /* mfctr */
170 regs->gpr[rd] = regs->ctr;
171 goto mtspr_out;
172 }
173 break;
174 case 0x378: /* orx */
175 rs = (instr >> 21) & 0x1f;
176 rb = (instr >> 11) & 0x1f;
177 if (rs == rb) { /* mr */
178 rd = (instr >> 16) & 0x1f;
179 regs->gpr[rd] = regs->gpr[rs];
180 goto mtspr_out;
181 }
182 break;
183 case 0x3a6: /* mtspr */
184 spr = (instr >> 11) & 0x3ff;
185 switch (spr) {
186 case 0x20: /* mtxer */
187 regs->xer = (regs->gpr[rd] & 0xffffffffUL);
188 goto mtspr_out;
189 case 0x100: /* mtlr */
190 regs->link = regs->gpr[rd];
191 goto mtspr_out;
192 case 0x120: /* mtctr */
193 regs->ctr = regs->gpr[rd];
194mtspr_out:
195 regs->nip += 4;
196 return 1;
197 }
Paul Mackerras14cf11a2005-09-26 16:04:21 +1000198 }
199 }
200 return 0;
201}