 
/*--------------------------------------------------------------------*/
/*--- Attaching a debugger.                           m_debugger.c ---*/
/*--------------------------------------------------------------------*/

/*
   This file is part of Valgrind, a dynamic binary instrumentation
   framework.

   Copyright (C) 2000-2012 Julian Seward 
      jseward@acm.org

   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.

   This program is distributed in the hope that it will be useful, but
   WITHOUT ANY WARRANTY; without even the implied warranty of
   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
   General Public License for more details.

   You should have received a copy of the GNU General Public License
   along with this program; if not, write to the Free Software
   Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA
   02111-1307, USA.

   The GNU General Public License is contained in the file COPYING.
*/

#include "pub_core_basics.h"
#include "pub_core_vki.h"
#include "pub_core_libcsetjmp.h"
#include "pub_core_threadstate.h"
#include "pub_core_xarray.h"
#include "pub_core_clientstate.h"
#include "pub_core_debugger.h"
#include "pub_core_libcbase.h"
#include "pub_core_libcprint.h"
#include "pub_core_libcproc.h"
#include "pub_core_libcsignal.h"
#include "pub_core_libcassert.h"
#include "pub_core_options.h"


#define WIFSTOPPED(status) (((status) & 0xff) == 0x7f)
#define WSTOPSIG(status) (((status) & 0xff00) >> 8)

static Int ptrace_setregs(Int pid, VexGuestArchState* vex)
{
#if defined(VGP_x86_linux)
   struct vki_user_regs_struct regs;
   VG_(memset)(&regs, 0, sizeof(regs));
   regs.cs     = vex->guest_CS;
   regs.ss     = vex->guest_SS;
   regs.ds     = vex->guest_DS;
   regs.es     = vex->guest_ES;
   regs.fs     = vex->guest_FS;
   regs.gs     = vex->guest_GS;
   regs.eax    = vex->guest_EAX;
   regs.ebx    = vex->guest_EBX;
   regs.ecx    = vex->guest_ECX;
   regs.edx    = vex->guest_EDX;
   regs.esi    = vex->guest_ESI;
   regs.edi    = vex->guest_EDI;
   regs.ebp    = vex->guest_EBP;
   regs.esp    = vex->guest_ESP;
   regs.eflags = LibVEX_GuestX86_get_eflags(vex);
   regs.eip    = vex->guest_EIP;
   return VG_(ptrace)(VKI_PTRACE_SETREGS, pid, NULL, &regs);

#elif defined(VGP_amd64_linux)
   struct vki_user_regs_struct regs;
   VG_(memset)(&regs, 0, sizeof(regs));
   regs.rax    = vex->guest_RAX;
   regs.rbx    = vex->guest_RBX;
   regs.rcx    = vex->guest_RCX;
   regs.rdx    = vex->guest_RDX;
   regs.rsi    = vex->guest_RSI;
   regs.rdi    = vex->guest_RDI;
   regs.rbp    = vex->guest_RBP;
   regs.rsp    = vex->guest_RSP;
   regs.r8     = vex->guest_R8;
   regs.r9     = vex->guest_R9;
   regs.r10    = vex->guest_R10;
   regs.r11    = vex->guest_R11;
   regs.r12    = vex->guest_R12;
   regs.r13    = vex->guest_R13;
   regs.r14    = vex->guest_R14;
   regs.r15    = vex->guest_R15;
   regs.eflags = LibVEX_GuestAMD64_get_rflags(vex);
   regs.rip    = vex->guest_RIP;
   /* Set %{c,d,e,f,s,g}s and %{fs,gs}_base (whatever those are) to
      values which don't fail the kernel's sanity checks.  I have no
      idea what these should really be set to.  Anyway, mostly it
      seems that zero is an allowable value, except for %cs and %ss
      which have to have their lowest 2 bits be 11.  See putreg() in
      linux-2.6.23/arch/x86_64/kernel/ptrace.c for the apparently
      relevant sanity checks.  This fixes #145622. */
   regs.cs      = 3;
   regs.ds      = 0;
   regs.es      = 0;
   regs.fs      = 0;
   regs.ss      = 3;
   regs.gs      = 0;
   regs.fs_base = 0;
   regs.gs_base = 0;
   return VG_(ptrace)(VKI_PTRACE_SETREGS, pid, NULL, &regs);

#elif defined(VGP_ppc32_linux)
   Int rc = 0;
   /* apparently the casting to void* is the Right Thing To Do */
   rc |= VG_(ptrace)(VKI_PTRACE_POKEUSR, pid, (void*)(VKI_PT_R0  * 4), (void*)vex->guest_GPR0);
   rc |= VG_(ptrace)(VKI_PTRACE_POKEUSR, pid, (void*)(VKI_PT_R1  * 4), (void*)vex->guest_GPR1);
   rc |= VG_(ptrace)(VKI_PTRACE_POKEUSR, pid, (void*)(VKI_PT_R2  * 4), (void*)vex->guest_GPR2);
   rc |= VG_(ptrace)(VKI_PTRACE_POKEUSR, pid, (void*)(VKI_PT_R3  * 4), (void*)vex->guest_GPR3);
   rc |= VG_(ptrace)(VKI_PTRACE_POKEUSR, pid, (void*)(VKI_PT_R4  * 4), (void*)vex->guest_GPR4);
   rc |= VG_(ptrace)(VKI_PTRACE_POKEUSR, pid, (void*)(VKI_PT_R5  * 4), (void*)vex->guest_GPR5);
   rc |= VG_(ptrace)(VKI_PTRACE_POKEUSR, pid, (void*)(VKI_PT_R6  * 4), (void*)vex->guest_GPR6);
   rc |= VG_(ptrace)(VKI_PTRACE_POKEUSR, pid, (void*)(VKI_PT_R7  * 4), (void*)vex->guest_GPR7);
   rc |= VG_(ptrace)(VKI_PTRACE_POKEUSR, pid, (void*)(VKI_PT_R8  * 4), (void*)vex->guest_GPR8);
   rc |= VG_(ptrace)(VKI_PTRACE_POKEUSR, pid, (void*)(VKI_PT_R9  * 4), (void*)vex->guest_GPR9);
   rc |= VG_(ptrace)(VKI_PTRACE_POKEUSR, pid, (void*)(VKI_PT_R10 * 4), (void*)vex->guest_GPR10);
   rc |= VG_(ptrace)(VKI_PTRACE_POKEUSR, pid, (void*)(VKI_PT_R11 * 4), (void*)vex->guest_GPR11);
   rc |= VG_(ptrace)(VKI_PTRACE_POKEUSR, pid, (void*)(VKI_PT_R12 * 4), (void*)vex->guest_GPR12);
   rc |= VG_(ptrace)(VKI_PTRACE_POKEUSR, pid, (void*)(VKI_PT_R13 * 4), (void*)vex->guest_GPR13);
   rc |= VG_(ptrace)(VKI_PTRACE_POKEUSR, pid, (void*)(VKI_PT_R14 * 4), (void*)vex->guest_GPR14);
   rc |= VG_(ptrace)(VKI_PTRACE_POKEUSR, pid, (void*)(VKI_PT_R15 * 4), (void*)vex->guest_GPR15);
   rc |= VG_(ptrace)(VKI_PTRACE_POKEUSR, pid, (void*)(VKI_PT_R16 * 4), (void*)vex->guest_GPR16);
   rc |= VG_(ptrace)(VKI_PTRACE_POKEUSR, pid, (void*)(VKI_PT_R17 * 4), (void*)vex->guest_GPR17);
   rc |= VG_(ptrace)(VKI_PTRACE_POKEUSR, pid, (void*)(VKI_PT_R18 * 4), (void*)vex->guest_GPR18);
   rc |= VG_(ptrace)(VKI_PTRACE_POKEUSR, pid, (void*)(VKI_PT_R19 * 4), (void*)vex->guest_GPR19);
   rc |= VG_(ptrace)(VKI_PTRACE_POKEUSR, pid, (void*)(VKI_PT_R20 * 4), (void*)vex->guest_GPR20);
   rc |= VG_(ptrace)(VKI_PTRACE_POKEUSR, pid, (void*)(VKI_PT_R21 * 4), (void*)vex->guest_GPR21);
   rc |= VG_(ptrace)(VKI_PTRACE_POKEUSR, pid, (void*)(VKI_PT_R22 * 4), (void*)vex->guest_GPR22);
   rc |= VG_(ptrace)(VKI_PTRACE_POKEUSR, pid, (void*)(VKI_PT_R23 * 4), (void*)vex->guest_GPR23);
   rc |= VG_(ptrace)(VKI_PTRACE_POKEUSR, pid, (void*)(VKI_PT_R24 * 4), (void*)vex->guest_GPR24);
   rc |= VG_(ptrace)(VKI_PTRACE_POKEUSR, pid, (void*)(VKI_PT_R25 * 4), (void*)vex->guest_GPR25);
   rc |= VG_(ptrace)(VKI_PTRACE_POKEUSR, pid, (void*)(VKI_PT_R26 * 4), (void*)vex->guest_GPR26);
   rc |= VG_(ptrace)(VKI_PTRACE_POKEUSR, pid, (void*)(VKI_PT_R27 * 4), (void*)vex->guest_GPR27);
   rc |= VG_(ptrace)(VKI_PTRACE_POKEUSR, pid, (void*)(VKI_PT_R28 * 4), (void*)vex->guest_GPR28);
   rc |= VG_(ptrace)(VKI_PTRACE_POKEUSR, pid, (void*)(VKI_PT_R29 * 4), (void*)vex->guest_GPR29);
   rc |= VG_(ptrace)(VKI_PTRACE_POKEUSR, pid, (void*)(VKI_PT_R30 * 4), (void*)vex->guest_GPR30);
   rc |= VG_(ptrace)(VKI_PTRACE_POKEUSR, pid, (void*)(VKI_PT_R31 * 4), (void*)vex->guest_GPR31);
   rc |= VG_(ptrace)(VKI_PTRACE_POKEUSR, pid, (void*)(VKI_PT_NIP * 4), (void*)vex->guest_CIA);
   rc |= VG_(ptrace)(VKI_PTRACE_POKEUSR, pid, (void*)(VKI_PT_CCR * 4),
                     (void*)LibVEX_GuestPPC32_get_CR(vex));
   rc |= VG_(ptrace)(VKI_PTRACE_POKEUSR, pid, (void*)(VKI_PT_LNK * 4), (void*)vex->guest_LR);
   rc |= VG_(ptrace)(VKI_PTRACE_POKEUSR, pid, (void*)(VKI_PT_CTR * 4), (void*)vex->guest_CTR);
   rc |= VG_(ptrace)(VKI_PTRACE_POKEUSR, pid, (void*)(VKI_PT_XER * 4),
                     (void*)LibVEX_GuestPPC32_get_XER(vex));
   return rc;

#elif defined(VGP_ppc64_linux)
   Int rc = 0; 
   /* FRJ: copied nearly verbatim from the ppc32 case. I compared the 
      vki-ppc64-linux.h with its ppc32 counterpart and saw no 
      appreciable differences, other than the registers being 8 bytes 
      instead of 4. No idea why we don't set all of the entries 
      declared in vki_pt_regs, but ppc32 doesn't so there must be a 
      reason. 
 
      Finally, note that CR and XER are 32 bits even for ppc64 (see 
      libvex_guest_ppc64.h), but the vki_pt_regs struct still gives 
      them 64 bits. 
   */ 
   /* apparently the casting to void* is the Right Thing To Do */ 
   rc |= VG_(ptrace)(VKI_PTRACE_POKEUSR, pid, (void*)(VKI_PT_R0  * 8), (void*)vex->guest_GPR0); 
   rc |= VG_(ptrace)(VKI_PTRACE_POKEUSR, pid, (void*)(VKI_PT_R1  * 8), (void*)vex->guest_GPR1); 
   rc |= VG_(ptrace)(VKI_PTRACE_POKEUSR, pid, (void*)(VKI_PT_R2  * 8), (void*)vex->guest_GPR2); 
   rc |= VG_(ptrace)(VKI_PTRACE_POKEUSR, pid, (void*)(VKI_PT_R3  * 8), (void*)vex->guest_GPR3); 
   rc |= VG_(ptrace)(VKI_PTRACE_POKEUSR, pid, (void*)(VKI_PT_R4  * 8), (void*)vex->guest_GPR4); 
   rc |= VG_(ptrace)(VKI_PTRACE_POKEUSR, pid, (void*)(VKI_PT_R5  * 8), (void*)vex->guest_GPR5); 
   rc |= VG_(ptrace)(VKI_PTRACE_POKEUSR, pid, (void*)(VKI_PT_R6  * 8), (void*)vex->guest_GPR6); 
   rc |= VG_(ptrace)(VKI_PTRACE_POKEUSR, pid, (void*)(VKI_PT_R7  * 8), (void*)vex->guest_GPR7); 
   rc |= VG_(ptrace)(VKI_PTRACE_POKEUSR, pid, (void*)(VKI_PT_R8  * 8), (void*)vex->guest_GPR8); 
   rc |= VG_(ptrace)(VKI_PTRACE_POKEUSR, pid, (void*)(VKI_PT_R9  * 8), (void*)vex->guest_GPR9); 
   rc |= VG_(ptrace)(VKI_PTRACE_POKEUSR, pid, (void*)(VKI_PT_R10 * 8), (void*)vex->guest_GPR10); 
   rc |= VG_(ptrace)(VKI_PTRACE_POKEUSR, pid, (void*)(VKI_PT_R11 * 8), (void*)vex->guest_GPR11); 
   rc |= VG_(ptrace)(VKI_PTRACE_POKEUSR, pid, (void*)(VKI_PT_R12 * 8), (void*)vex->guest_GPR12); 
   rc |= VG_(ptrace)(VKI_PTRACE_POKEUSR, pid, (void*)(VKI_PT_R13 * 8), (void*)vex->guest_GPR13); 
   rc |= VG_(ptrace)(VKI_PTRACE_POKEUSR, pid, (void*)(VKI_PT_R14 * 8), (void*)vex->guest_GPR14); 
   rc |= VG_(ptrace)(VKI_PTRACE_POKEUSR, pid, (void*)(VKI_PT_R15 * 8), (void*)vex->guest_GPR15); 
   rc |= VG_(ptrace)(VKI_PTRACE_POKEUSR, pid, (void*)(VKI_PT_R16 * 8), (void*)vex->guest_GPR16); 
   rc |= VG_(ptrace)(VKI_PTRACE_POKEUSR, pid, (void*)(VKI_PT_R17 * 8), (void*)vex->guest_GPR17); 
   rc |= VG_(ptrace)(VKI_PTRACE_POKEUSR, pid, (void*)(VKI_PT_R18 * 8), (void*)vex->guest_GPR18); 
   rc |= VG_(ptrace)(VKI_PTRACE_POKEUSR, pid, (void*)(VKI_PT_R19 * 8), (void*)vex->guest_GPR19); 
   rc |= VG_(ptrace)(VKI_PTRACE_POKEUSR, pid, (void*)(VKI_PT_R20 * 8), (void*)vex->guest_GPR20); 
   rc |= VG_(ptrace)(VKI_PTRACE_POKEUSR, pid, (void*)(VKI_PT_R21 * 8), (void*)vex->guest_GPR21); 
   rc |= VG_(ptrace)(VKI_PTRACE_POKEUSR, pid, (void*)(VKI_PT_R22 * 8), (void*)vex->guest_GPR22); 
   rc |= VG_(ptrace)(VKI_PTRACE_POKEUSR, pid, (void*)(VKI_PT_R23 * 8), (void*)vex->guest_GPR23); 
   rc |= VG_(ptrace)(VKI_PTRACE_POKEUSR, pid, (void*)(VKI_PT_R24 * 8), (void*)vex->guest_GPR24); 
   rc |= VG_(ptrace)(VKI_PTRACE_POKEUSR, pid, (void*)(VKI_PT_R25 * 8), (void*)vex->guest_GPR25); 
   rc |= VG_(ptrace)(VKI_PTRACE_POKEUSR, pid, (void*)(VKI_PT_R26 * 8), (void*)vex->guest_GPR26); 
   rc |= VG_(ptrace)(VKI_PTRACE_POKEUSR, pid, (void*)(VKI_PT_R27 * 8), (void*)vex->guest_GPR27); 
   rc |= VG_(ptrace)(VKI_PTRACE_POKEUSR, pid, (void*)(VKI_PT_R28 * 8), (void*)vex->guest_GPR28); 
   rc |= VG_(ptrace)(VKI_PTRACE_POKEUSR, pid, (void*)(VKI_PT_R29 * 8), (void*)vex->guest_GPR29); 
   rc |= VG_(ptrace)(VKI_PTRACE_POKEUSR, pid, (void*)(VKI_PT_R30 * 8), (void*)vex->guest_GPR30); 
   rc |= VG_(ptrace)(VKI_PTRACE_POKEUSR, pid, (void*)(VKI_PT_R31 * 8), (void*)vex->guest_GPR31); 
   rc |= VG_(ptrace)(VKI_PTRACE_POKEUSR, pid, (void*)(VKI_PT_NIP * 8), (void*)vex->guest_CIA); 
   rc |= VG_(ptrace)(VKI_PTRACE_POKEUSR, pid, (void*)(VKI_PT_CCR * 8), 
                                              (void*)(long)LibVEX_GuestPPC64_get_CR(vex)); 
   rc |= VG_(ptrace)(VKI_PTRACE_POKEUSR, pid, (void*)(VKI_PT_LNK * 8), (void*)vex->guest_LR); 
   rc |= VG_(ptrace)(VKI_PTRACE_POKEUSR, pid, (void*)(VKI_PT_CTR * 8), (void*)vex->guest_CTR); 
   rc |= VG_(ptrace)(VKI_PTRACE_POKEUSR, pid, (void*)(VKI_PT_XER * 8), 
                                              (void*)(long)LibVEX_GuestPPC64_get_XER(vex)); 
   return rc; 

#elif defined(VGP_arm_linux)
   struct vki_user_regs_struct uregs;
   VG_(memset)(&uregs, 0, sizeof(uregs));
   uregs.ARM_r0   = vex->guest_R0; 
   uregs.ARM_r1   = vex->guest_R1; 
   uregs.ARM_r2   = vex->guest_R2; 
   uregs.ARM_r3   = vex->guest_R3; 
   uregs.ARM_r4   = vex->guest_R4; 
   uregs.ARM_r5   = vex->guest_R5; 
   uregs.ARM_r6   = vex->guest_R6; 
   uregs.ARM_r7   = vex->guest_R7; 
   uregs.ARM_r8   = vex->guest_R8; 
   uregs.ARM_r9   = vex->guest_R9; 
   uregs.ARM_r10  = vex->guest_R10; 
   uregs.ARM_fp   = vex->guest_R11; 
   uregs.ARM_ip   = vex->guest_R12; 
   uregs.ARM_sp   = vex->guest_R13; 
   uregs.ARM_lr   = vex->guest_R14; 
   // Remove the T bit from the bottom of R15T.  It will get shipped
   // over in CPSR.T instead, since LibVEX_GuestARM_get_cpsr copies
   // it from R15T[0].
   uregs.ARM_pc   = vex->guest_R15T & 0xFFFFFFFE;
   uregs.ARM_cpsr = LibVEX_GuestARM_get_cpsr(vex);
   return VG_(ptrace)(VKI_PTRACE_SETREGS, pid, NULL, &uregs);

#elif defined(VGP_x86_darwin)
   I_die_here;

#elif defined(VGP_x86_freebsd)
   I_die_here;

#elif defined(VGP_amd64_freebsd)
   I_die_here;

#elif defined(VGP_amd64_darwin)
   I_die_here;

#elif defined(VGP_s390x_linux)
   struct vki_user_regs_struct regs;
   vki_ptrace_area pa;

   /* We don't set the psw mask and start at offset 8 */
   pa.vki_len = (unsigned long) &regs.per_info - (unsigned long) &regs.psw.addr;
   pa.vki_process_addr = (unsigned long) &regs.psw.addr;
   pa.vki_kernel_addr = 8;

   VG_(memset)(&regs, 0, sizeof(regs));
   regs.psw.addr = vex->guest_IA;

   /* We don't set the mask */
   regs.gprs[0] = vex->guest_r0;
   regs.gprs[1] = vex->guest_r1;
   regs.gprs[2] = vex->guest_r2;
   regs.gprs[3] = vex->guest_r3;
   regs.gprs[4] = vex->guest_r4;
   regs.gprs[5] = vex->guest_r5;
   regs.gprs[6] = vex->guest_r6;
   regs.gprs[7] = vex->guest_r7;
   regs.gprs[8] = vex->guest_r8;
   regs.gprs[9] = vex->guest_r9;
   regs.gprs[10] = vex->guest_r10;
   regs.gprs[11] = vex->guest_r11;
   regs.gprs[12] = vex->guest_r12;
   regs.gprs[13] = vex->guest_r13;
   regs.gprs[14] = vex->guest_r14;
   regs.gprs[15] = vex->guest_r15;

   regs.acrs[0] = vex->guest_a0;
   regs.acrs[1] = vex->guest_a1;
   regs.acrs[2] = vex->guest_a2;
   regs.acrs[3] = vex->guest_a3;
   regs.acrs[4] = vex->guest_a4;
   regs.acrs[5] = vex->guest_a5;
   regs.acrs[6] = vex->guest_a6;
   regs.acrs[7] = vex->guest_a7;
   regs.acrs[8] = vex->guest_a8;
   regs.acrs[9] = vex->guest_a9;
   regs.acrs[10] = vex->guest_a10;
   regs.acrs[11] = vex->guest_a11;
   regs.acrs[12] = vex->guest_a12;
   regs.acrs[13] = vex->guest_a13;
   regs.acrs[14] = vex->guest_a14;
   regs.acrs[15] = vex->guest_a15;

   /* only used for system call restart and friends, just use r2 */
   regs.orig_gpr2 = vex->guest_r2;

   regs.fp_regs.fprs[0].ui = vex->guest_f0;
   regs.fp_regs.fprs[1].ui = vex->guest_f1;
   regs.fp_regs.fprs[2].ui = vex->guest_f2;
   regs.fp_regs.fprs[3].ui = vex->guest_f3;
   regs.fp_regs.fprs[4].ui = vex->guest_f4;
   regs.fp_regs.fprs[5].ui = vex->guest_f5;
   regs.fp_regs.fprs[6].ui = vex->guest_f6;
   regs.fp_regs.fprs[7].ui = vex->guest_f7;
   regs.fp_regs.fprs[8].ui = vex->guest_f8;
   regs.fp_regs.fprs[9].ui = vex->guest_f9;
   regs.fp_regs.fprs[10].ui = vex->guest_f10;
   regs.fp_regs.fprs[11].ui = vex->guest_f11;
   regs.fp_regs.fprs[12].ui = vex->guest_f12;
   regs.fp_regs.fprs[13].ui = vex->guest_f13;
   regs.fp_regs.fprs[14].ui = vex->guest_f14;
   regs.fp_regs.fprs[15].ui = vex->guest_f15;
   regs.fp_regs.fpc = vex->guest_fpc;

   return VG_(ptrace)(VKI_PTRACE_POKEUSR_AREA, pid,  &pa, NULL);

#elif defined(VGP_mips32_linux)
   struct vki_user_regs_struct regs;
   VG_(memset)(&regs, 0, sizeof(regs));
   regs.MIPS_r0     = vex->guest_r0;
   regs.MIPS_r1     = vex->guest_r1;
   regs.MIPS_r2     = vex->guest_r2;
   regs.MIPS_r3     = vex->guest_r3;
   regs.MIPS_r4     = vex->guest_r4;
   regs.MIPS_r5     = vex->guest_r5;
   regs.MIPS_r6     = vex->guest_r6;
   regs.MIPS_r7     = vex->guest_r7;
   regs.MIPS_r8     = vex->guest_r8;
   regs.MIPS_r9     = vex->guest_r9;
   regs.MIPS_r10     = vex->guest_r10;
   regs.MIPS_r11     = vex->guest_r11;
   regs.MIPS_r12     = vex->guest_r12;
   regs.MIPS_r13     = vex->guest_r13;
   regs.MIPS_r14     = vex->guest_r14;
   regs.MIPS_r15     = vex->guest_r15;
   regs.MIPS_r16     = vex->guest_r16;
   regs.MIPS_r17     = vex->guest_r17;
   regs.MIPS_r18     = vex->guest_r18;
   regs.MIPS_r19     = vex->guest_r19;
   regs.MIPS_r20     = vex->guest_r20;
   regs.MIPS_r21     = vex->guest_r21;
   regs.MIPS_r22     = vex->guest_r22;
   regs.MIPS_r23     = vex->guest_r23;
   regs.MIPS_r24     = vex->guest_r24;
   regs.MIPS_r25     = vex->guest_r25;
   regs.MIPS_r26     = vex->guest_r26;
   regs.MIPS_r27     = vex->guest_r27;
   regs.MIPS_r28     = vex->guest_r28;
   regs.MIPS_r29     = vex->guest_r29;
   regs.MIPS_r30     = vex->guest_r30;
   regs.MIPS_r31     = vex->guest_r31;
   return VG_(ptrace)(VKI_PTRACE_SETREGS, pid, NULL, &regs);

#else
#  error Unknown arch
#endif
}

/* Start debugger and get it to attach to this process.  Called if the
   user requests this service after an error has been shown, so she can
   poke around and look at parameters, memory, etc.  You can't
   meaningfully get the debugger to continue the program, though; to
   continue, quit the debugger.  */
void VG_(start_debugger) ( ThreadId tid )
{
#  define N_BUF 4096
   Int pid, rc;

   pid = VG_(fork)();

   if (pid == 0) {
      /* child */
      rc = VG_(ptrace)(VKI_PTRACE_TRACEME, 0, NULL, NULL);
      vg_assert(rc == 0);
      rc = VG_(kill)(VG_(getpid)(), VKI_SIGSTOP);
      vg_assert(rc == 0);

   } else if (pid > 0) {
      /* parent */
      Int status;
      Int res;

      if ((res = VG_(waitpid)(pid, &status, 0)) == pid &&
          WIFSTOPPED(status) && WSTOPSIG(status) == VKI_SIGSTOP &&
          ptrace_setregs(pid, &(VG_(threads)[tid].arch.vex)) == 0 &&
          VG_(kill)(pid, VKI_SIGSTOP) == 0 &&
          VG_(ptrace)(VKI_PTRACE_DETACH, pid, NULL, 0) == 0)
      {
         Char pidbuf[15];
         Char file[50];
         Char buf[N_BUF];
         Char *bufptr;
         Char *cmdptr;
         
         VG_(sprintf)(pidbuf, "%d", pid);
         VG_(sprintf)(file, "/proc/%d/fd/%d", pid, VG_(cl_exec_fd));
 
         bufptr = buf;
         cmdptr = VG_(clo_db_command);
         
         while (*cmdptr) {
            /* each iteration can advance bufptr by at most the length
               of file[], so the following assertion is generously
               over-paranoid. */
            vg_assert(bufptr - buf < N_BUF-15-50-10/*paranoia*/);
            switch (*cmdptr) {
               case '%':
                  switch (*++cmdptr) {
                     case 'f':
                        VG_(memcpy)(bufptr, file, VG_(strlen)(file));
                        bufptr += VG_(strlen)(file);
                        cmdptr++;
                        break;
                     case 'p':
                        VG_(memcpy)(bufptr, pidbuf, VG_(strlen)(pidbuf));
                        bufptr += VG_(strlen)(pidbuf);
                        cmdptr++;
                        break;
                     default:
                        *bufptr++ = *cmdptr++;
                        break;
                  }
                  break;
               default:
                  *bufptr++ = *cmdptr++;
                  break;
            }
            vg_assert(bufptr - buf < N_BUF-15-50-10/*paranoia*/);
         }
         
         *bufptr++ = '\0';
  
         VG_(message)(Vg_UserMsg, "starting debugger with cmd: %s\n", buf);
         res = VG_(system)(buf);
         if (res == 0) {      
            VG_(message)(Vg_UserMsg, "\n");
            VG_(message)(Vg_UserMsg, 
                         "Debugger has detached.  Valgrind regains control."
                         "  We continue.\n");
         } else {
            VG_(message)(Vg_UserMsg, 
                         "Warning: Debugger attach failed! (sys_system)\n");
            VG_(message)(Vg_UserMsg, "\n");
         }
      } else {
         VG_(message)(Vg_UserMsg, 
                      "Warning: Debugger attach failed! (ptrace problem?)\n");
         VG_(message)(Vg_UserMsg, "\n");
      }

      VG_(kill)(pid, VKI_SIGKILL);
      VG_(waitpid)(pid, &status, 0);
   }
#  undef N_BUF
}



/*--------------------------------------------------------------------*/
/*--- end                                                          ---*/
/*--------------------------------------------------------------------*/
