arch/powerpc/lib/sstep.c

   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/kprobes.h>
  13 #include <linux/ptrace.h>
  14 #include <asm/sstep.h>
  15 #include <asm/processor.h>
  16
  17 extern char system_call_common[];
  18
  19 #ifdef CONFIG_PPC64
  20 /* Bits in SRR1 that are copied from MSR */
  21 #define MSR_MASK        0xffffffff87c0ffffUL
  22 #else
  23 #define MSR_MASK        0x87c0ffff
  24 #endif
  25
  26 /*
  27  * Determine whether a conditional branch instruction would branch.
  28  */
  29 static int __kprobes branch_taken(unsigned int instr, struct pt_regs *regs)
  30 {
  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  */
  55 int __kprobes emulate_step(struct pt_regs *regs, unsigned int instr)
  56 {
  57         unsigned int opcode, rd;
  58         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;
  74 #ifdef CONFIG_PPC64
  75         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;
  88 #endif
  89         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;
 131                 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
 140                 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;
 154 #endif
 155                 }
 156         }
 157         return 0;
 158 }