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 16 extern char system_call_common[]; 17 18 #ifdef CONFIG_PPC64 19 /* Bits in SRR1 that are copied from MSR */ 20 #define MSR_MASK 0xffffffff87c0ffffUL 21 #else 22 #define MSR_MASK 0x87c0ffff 23 #endif 24 25 /* 26 * Determine whether a conditional branch instruction would branch. 27 */ 28 static int branch_taken(unsigned int instr, struct pt_regs *regs) 29 { 30 unsigned int bo = (instr >> 21) & 0x1f; 31 unsigned int bi; 32 33 if ((bo & 4) == 0) { 34 /* decrement counter */ 35 --regs->ctr; 36 if (((bo >> 1) & 1) ^ (regs->ctr == 0)) 37 return 0; 38 } 39 if ((bo & 0x10) == 0) { 40 /* check bit from CR */ 41 bi = (instr >> 16) & 0x1f; 42 if (((regs->ccr >> (31 - bi)) & 1) != ((bo >> 3) & 1)) 43 return 0; 44 } 45 return 1; 46 } 47 48 /* 49 * Emulate instructions that cause a transfer of control. 50 * Returns 1 if the step was emulated, 0 if not, 51 * or -1 if the instruction is one that should not be stepped, 52 * such as an rfid, or a mtmsrd that would clear MSR_RI. 53 */ 54 int emulate_step(struct pt_regs *regs, unsigned int instr) 55 { 56 unsigned int opcode, rd; 57 unsigned long int imm; 58 59 opcode = instr >> 26; 60 switch (opcode) { 61 case 16: /* bc */ 62 imm = (signed short)(instr & 0xfffc); 63 if ((instr & 2) == 0) 64 imm += regs->nip; 65 regs->nip += 4; 66 if ((regs->msr & MSR_SF) == 0) 67 regs->nip &= 0xffffffffUL; 68 if (instr & 1) 69 regs->link = regs->nip; 70 if (branch_taken(instr, regs)) 71 regs->nip = imm; 72 return 1; 73 #ifdef CONFIG_PPC64 74 case 17: /* sc */ 75 /* 76 * N.B. this uses knowledge about how the syscall 77 * entry code works. If that is changed, this will 78 * need to be changed also. 79 */ 80 regs->gpr[9] = regs->gpr[13]; 81 regs->gpr[11] = regs->nip + 4; 82 regs->gpr[12] = regs->msr & MSR_MASK; 83 regs->gpr[13] = (unsigned long) get_paca(); 84 regs->nip = (unsigned long) &system_call_common; 85 regs->msr = MSR_KERNEL; 86 return 1; 87 #endif 88 case 18: /* b */ 89 imm = instr & 0x03fffffc; 90 if (imm & 0x02000000) 91 imm -= 0x04000000; 92 if ((instr & 2) == 0) 93 imm += regs->nip; 94 if (instr & 1) { 95 regs->link = regs->nip + 4; 96 if ((regs->msr & MSR_SF) == 0) 97 regs->link &= 0xffffffffUL; 98 } 99 if ((regs->msr & MSR_SF) == 0) 100 imm &= 0xffffffffUL; 101 regs->nip = imm; 102 return 1; 103 case 19: 104 switch (instr & 0x7fe) { 105 case 0x20: /* bclr */ 106 case 0x420: /* bcctr */ 107 imm = (instr & 0x400)? regs->ctr: regs->link; 108 regs->nip += 4; 109 if ((regs->msr & MSR_SF) == 0) { 110 regs->nip &= 0xffffffffUL; 111 imm &= 0xffffffffUL; 112 } 113 if (instr & 1) 114 regs->link = regs->nip; 115 if (branch_taken(instr, regs)) 116 regs->nip = imm; 117 return 1; 118 case 0x24: /* rfid, scary */ 119 return -1; 120 } 121 case 31: 122 rd = (instr >> 21) & 0x1f; 123 switch (instr & 0x7fe) { 124 case 0xa6: /* mfmsr */ 125 regs->gpr[rd] = regs->msr & MSR_MASK; 126 regs->nip += 4; 127 if ((regs->msr & MSR_SF) == 0) 128 regs->nip &= 0xffffffffUL; 129 return 1; 130 case 0x124: /* mtmsr */ 131 imm = regs->gpr[rd]; 132 if ((imm & MSR_RI) == 0) 133 /* can't step mtmsr that would clear MSR_RI */ 134 return -1; 135 regs->msr = imm; 136 regs->nip += 4; 137 return 1; 138 #ifdef CONFIG_PPC64 139 case 0x164: /* mtmsrd */ 140 /* only MSR_EE and MSR_RI get changed if bit 15 set */ 141 /* mtmsrd doesn't change MSR_HV and MSR_ME */ 142 imm = (instr & 0x10000)? 0x8002: 0xefffffffffffefffUL; 143 imm = (regs->msr & MSR_MASK & ~imm) 144 | (regs->gpr[rd] & imm); 145 if ((imm & MSR_RI) == 0) 146 /* can't step mtmsrd that would clear MSR_RI */ 147 return -1; 148 regs->msr = imm; 149 regs->nip += 4; 150 if ((imm & MSR_SF) == 0) 151 regs->nip &= 0xffffffffUL; 152 return 1; 153 #endif 154 } 155 } 156 return 0; 157 } 158