Porting valgrind.h to win32?

[Dan Kegel-2]

win32 apps run pretty well in wine in valgrind.  Great!
But at the moment, valgrind.h doesn't support win32,
so win32 apps can't do client requests, which
means that you can't instrument the win32 app's
heap.

So I read up on gcc inline assembler syntax, and looked
at valgrind.h... but rather than rot my brain, I decided to
use objdump to display the bytes of a simple
linux app that calls VALGRIND_PRINT.
__SPECIAL_INSTRUCTION_PREAMBLE
appears to expand to
    48 c1 c7 03             rol    $0x3,%rdi
    48 c1 c7 0d             rol    $0xd,%rdi
    48 c1 c7 3d             rol    $0x3d,%rdi
    48 c1 c7 33             rol    $0x33,%rdi

while the key bit of VALGRIND_DO_CLIENT_REQUEST
which immediately follows the preamble expands to
    48 87 db                xchg   %rbx,%rbx

I'm a bit mystified by all the 0x48 prefixes.  I thought
0x48 was dec ax ... what's going on there?

In spite of not understanding this, I had a shot at porting
VALGRIND_PRINTF.  Here's a little test program that
should display "Hello, valgrind" and then a warning about
exit's argument being undefined when run either as a native
linux app, e.g.
  gcc valprint.c
  valgrind ./a.out
or as a win32 app under wine:
  cl valprint.c
  (transfer to linux system)
  wine winemine &    (to avoid valgrinding service startup)
  valgrind --trace-children=yes wine valprint.exe

Works fine on linux, and on Wine the exit(undefined)
warning shows up fine, but my implementation of
VALGRIND_PRINTF seems to be a no-op :-(

Here's the test program.  Anyone adventurous feel like having a look?

#include <malloc.h>
#ifdef _WIN32
#include <stdlib.h>
#include <stdarg.h>
#define __SPECIAL_INSTRUCTION_PREAMBLE __asm { \
    __asm _emit 0x48 __asm _emit 0xc1 __asm _emit 0xc7 __asm _emit 0x03 \
    __asm _emit 0x48 __asm _emit 0xc1 __asm _emit 0xc7 __asm _emit 0x0d \
    __asm _emit 0x48 __asm _emit 0xc1 __asm _emit 0xc7 __asm _emit 0x3d \
    __asm _emit 0x48 __asm _emit 0xc1 __asm _emit 0xc7 __asm _emit 0x33 \
  }
enum { VG_USERREQ__RUNNING_ON_VALGRIND  = 0x1001,
       VG_USERREQ__PRINTF           = 0x1401,
} Vg_ClientRequest;
static int
VALGRIND_PRINTF(const char *format, ...)
{
   va_list vargs;
   volatile unsigned int _zzq_args[6];
   unsigned int _qzz_res;
   va_start(vargs, format);
   _zzq_args[0] = (unsigned int) VG_USERREQ__PRINTF,
   _zzq_args[1] = (unsigned int) format;
   _zzq_args[2] = (unsigned int) vargs;
   _zzq_args[3] = (unsigned int) 0;
   _zzq_args[4] = (unsigned int) 0;
   _zzq_args[5] = (unsigned int) 0;
   __asm mov eax, _zzq_args
   __asm mov edx, 0
   __SPECIAL_INSTRUCTION_PREAMBLE
   __asm xchg ebx,ebx
   __asm mov _qzz_res, edx
   va_end(vargs);
   return (int)_qzz_res;
}
#else
#include <valgrind/valgrind.h>
#endif

int main()
{
    char *memory = malloc(10);
    VALGRIND_PRINTF("Hello, valgrind!\n");
    return memory[0];
}

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[Dan Kegel-2]

I extended my demo program to support mingw32,
and got VALGRIND_PRINTF to work from a win32
app that way.  Now we just need to figure out what
went wrong in my trial port of valgrind.h to visual C.

Filed enhancement request for this at
https://bugs.kde.org/show_bug.cgi?id=210935

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On 18/10/09 02:37, Dan Kegel wrote:

> while the key bit of VALGRIND_DO_CLIENT_REQUEST
> which immediately follows the preamble expands to
>      48 87 db                xchg   %rbx,%rbx
>
> I'm a bit mystified by all the 0x48 prefixes.  I thought
> 0x48 was dec ax ... what's going on there?

It might be "dec ax" in 32 bit code but this is 64 bit code so it's a
REX prefix, used to access the extra registers.

Tom

--
Tom Hughes (tom@...)
http://www.compton.nu/

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[Dan Kegel-2]

Thanks to Tom and John, I now use 32 bit opcodes, and it
works a lot better :-)

My little demo still doesn't quite work when compiled
with visual c++ -- valgrind explodes with a SIGSEGV,
so either I have a bug, or varargs is different enough to
cause trouble.
I have to run, but if anyone's curious, here's what I've got so far.
- Dan

/* Demo of calling VALGRIND_PRINTF
 * See https://bugs.kde.org/show_bug.cgi?id=210935
 *
 * Works under Linux if compiled natively or if compiled with
 * mingw32 and run under Wine.
 * Doesn't quite work yet if compiled under Visual C++.
 * Dan Kegel 18 Oct 2009
 */

#include <malloc.h>

#if defined(linux)

#include <valgrind/valgrind.h>

#elif defined(_WIN32)

/* Subset of valgrind.h, ported to win32 for compilers mingw and visual c */

#include <stdlib.h>
#include <stdarg.h>

enum { VG_USERREQ__PRINTF           = 0x1401,
} Vg_ClientRequest;

#if defined(__GNUC__)

/* no changes needed in the gcc case;
 * valgrind.h just needs conditionals changed a bit
 * to recongnize that it works under gcc regardless of operating system
 */

#define __SPECIAL_INSTRUCTION_PREAMBLE                            \
                     "roll $3,  %%edi ; roll $13, %%edi\n\t"      \
                     "roll $29, %%edi ; roll $19, %%edi\n\t"

#define VALGRIND_DO_CLIENT_REQUEST(                               \
        _zzq_rlval, _zzq_default, _zzq_request,                   \
        _zzq_arg1, _zzq_arg2, _zzq_arg3, _zzq_arg4, _zzq_arg5)    \
  { volatile unsigned int _zzq_args[6];                           \
    volatile unsigned int _zzq_result;                            \
    _zzq_args[0] = (unsigned int)(_zzq_request);                  \
    _zzq_args[1] = (unsigned int)(_zzq_arg1);                     \
    _zzq_args[2] = (unsigned int)(_zzq_arg2);                     \
    _zzq_args[3] = (unsigned int)(_zzq_arg3);                     \
    _zzq_args[4] = (unsigned int)(_zzq_arg4);                     \
    _zzq_args[5] = (unsigned int)(_zzq_arg5);                     \
    __asm__ volatile(__SPECIAL_INSTRUCTION_PREAMBLE               \
                     /* %EDX = client_request ( %EAX ) */         \
                     "xchgl %%ebx,%%ebx"                          \
                     : "=d" (_zzq_result)                         \
                     : "a" (&_zzq_args[0]), "0" (_zzq_default)    \
                     : "cc", "memory"                             \
                    );                                            \
    _zzq_rlval = _zzq_result;                                     \
  }

static int VALGRIND_PRINTF(const char *format, ...)
   __attribute__((format(__printf__, 1, 2), __unused__));
static int
VALGRIND_PRINTF(const char *format, ...)
{
   unsigned long _qzz_res;
   va_list vargs;
   va_start(vargs, format);
   VALGRIND_DO_CLIENT_REQUEST(_qzz_res, 0, VG_USERREQ__PRINTF,
                              (unsigned long)format, (unsigned long)vargs,
                              0, 0, 0);
   va_end(vargs);
   return (int)_qzz_res;
}

#else

/* definitions from valgrind.h, ported to visual c */
/* This is for 32 bits; for 64 bits, shift counts are different */

#define __SPECIAL_INSTRUCTION_PREAMBLE __asm { \
    __asm rol edi, 0x03 \
    __asm rol edi, 0x0d \
    __asm rol edi, 0x1d \
    __asm rol edi, 0x13 \
  }

static int
VALGRIND_PRINTF(const char *format, ...)
{
   va_list vargs;
   volatile unsigned int _zzq_args[6];
   unsigned int _qzz_res;

   va_start(vargs, format);
   _zzq_args[0] = (unsigned int) VG_USERREQ__PRINTF,
   _zzq_args[1] = (unsigned int) format;
   _zzq_args[2] = (unsigned int) vargs;
   _zzq_args[3] = (unsigned int) 0;
   _zzq_args[4] = (unsigned int) 0;
   _zzq_args[5] = (unsigned int) 0;
   __asm mov eax, _zzq_args
   __asm mov edx, 0
   __SPECIAL_INSTRUCTION_PREAMBLE
   __asm xchg ebx,ebx
   __asm mov _qzz_res, edx
   va_end(vargs);
   return (int)_qzz_res;
}
#endif  /* defined(__GCC__) */
#endif  /* defined(_WIN32) */

int main()
{
    char *memory = malloc(10);

    VALGRIND_PRINTF("Hello, valgrind!\n");
    return memory[0];
}

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