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/*
* Single-step support.
*
* Copyright (C) 2004 Paul Mackerras <paulus@au.ibm.com>, IBM
*
* This program is free software; you can redistribute it and/or
* modify it under the terms of the GNU General Public License
* as published by the Free Software Foundation; either version
* 2 of the License, or (at your option) any later version.
*/
#include <linux/kernel.h>
#include <linux/ptrace.h>
#include <asm/sstep.h>
#include <asm/processor.h>
extern char system_call_common[];
/* Bits in SRR1 that are copied from MSR */
#define MSR_MASK 0xffffffff87c0ffff
/*
* Determine whether a conditional branch instruction would branch.
*/
static int branch_taken(unsigned int instr, struct pt_regs *regs)
{
unsigned int bo = (instr >> 21) & 0x1f;
unsigned int bi;
if ((bo & 4) == 0) {
/* decrement counter */
--regs->ctr;
if (((bo >> 1) & 1) ^ (regs->ctr == 0))
return 0;
}
if ((bo & 0x10) == 0) {
/* check bit from CR */
bi = (instr >> 16) & 0x1f;
if (((regs->ccr >> (31 - bi)) & 1) != ((bo >> 3) & 1))
return 0;
}
return 1;
}
/*
* Emulate instructions that cause a transfer of control.
* Returns 1 if the step was emulated, 0 if not,
* or -1 if the instruction is one that should not be stepped,
* such as an rfid, or a mtmsrd that would clear MSR_RI.
*/
int emulate_step(struct pt_regs *regs, unsigned int instr)
{
unsigned int opcode, rd;
unsigned long int imm;
opcode = instr >> 26;
switch (opcode) {
case 16: /* bc */
imm = (signed short)(instr & 0xfffc);
if ((instr & 2) == 0)
imm += regs->nip;
regs->nip += 4;
if ((regs->msr & MSR_SF) == 0)
regs->nip &= 0xffffffffUL;
if (instr & 1)
regs->link = regs->nip;
if (branch_taken(instr, regs))
regs->nip = imm;
return 1;
case 17: /* sc */
/*
* N.B. this uses knowledge about how the syscall
* entry code works. If that is changed, this will
* need to be changed also.
*/
regs->gpr[9] = regs->gpr[13];
regs->gpr[11] = regs->nip + 4;
regs->gpr[12] = regs->msr & MSR_MASK;
regs->gpr[13] = (unsigned long) get_paca();
regs->nip = (unsigned long) &system_call_common;
regs->msr = MSR_KERNEL;
return 1;
case 18: /* b */
imm = instr & 0x03fffffc;
if (imm & 0x02000000)
imm -= 0x04000000;
if ((instr & 2) == 0)
imm += regs->nip;
if (instr & 1) {
regs->link = regs->nip + 4;
if ((regs->msr & MSR_SF) == 0)
regs->link &= 0xffffffffUL;
}
if ((regs->msr & MSR_SF) == 0)
imm &= 0xffffffffUL;
regs->nip = imm;
return 1;
case 19:
switch (instr & 0x7fe) {
case 0x20: /* bclr */
case 0x420: /* bcctr */
imm = (instr & 0x400)? regs->ctr: regs->link;
regs->nip += 4;
if ((regs->msr & MSR_SF) == 0) {
regs->nip &= 0xffffffffUL;
imm &= 0xffffffffUL;
}
if (instr & 1)
regs->link = regs->nip;
if (branch_taken(instr, regs))
regs->nip = imm;
return 1;
case 0x24: /* rfid, scary */
return -1;
}
case 31:
rd = (instr >> 21) & 0x1f;
switch (instr & 0x7fe) {
case 0xa6: /* mfmsr */
regs->gpr[rd] = regs->msr & MSR_MASK;
regs->nip += 4;
if ((regs->msr & MSR_SF) == 0)
regs->nip &= 0xffffffffUL;
return 1;
case 0x164: /* mtmsrd */
/* only MSR_EE and MSR_RI get changed if bit 15 set */
/* mtmsrd doesn't change MSR_HV and MSR_ME */
imm = (instr & 0x10000)? 0x8002: 0xefffffffffffefffUL;
imm = (regs->msr & MSR_MASK & ~imm)
| (regs->gpr[rd] & imm);
if ((imm & MSR_RI) == 0)
/* can't step mtmsrd that would clear MSR_RI */
return -1;
regs->msr = imm;
regs->nip += 4;
if ((imm & MSR_SF) == 0)
regs->nip &= 0xffffffffUL;
return 1;
}
}
return 0;
}
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