[Valgrind-users] Valgrind on non-Linux platforms

[Matthew E. <ma...@gs...>]

Hi all,

There has been increasing interest in using Valgrind on the FreeBSD platform
and I have been working off and on to make this a reality since the 1.0.0
days.  My code base is now a hacked up version of 1.9.5 with very limited
functionality.  (No pthreads or LDT support.)

One of the largest stumbling blocks has been the various Linux-isms that are
present in the code, which are expected given the code's history.  The two
most major problems which can be addressed by architecture are the use of
hard-coded syscall names and hard-coded pthread internal variable names.

What follows are a couple of proposals that will assist porting valgrind to
non-Linux platforms.

I appreciate any feedback that you may have.

1) Introduce a mapping layer for syscall #defines.

As near as I can tell, all the syscalls referred to outside of vg_syscalls.c
are generic, POSIX-mandated syscalls (exit, execve, getpid, gettimeofday,
etc), and should be present on all UNIX platforms, thus no platform-specific
code outside of vg_syscalls.c.

I propose introducing a vg_syscall.h file that maps the platform's syscall
#defines to valgrind-specific #defines.  This would limit the scope of the
syscall-related changes required on non-Linux platforms to vg_syscalls.[ch],
rather than <n> files (<n> currently 7 on FreeBSD) just to patch up the __NR
syscall symbols.

Although this means another file to keep updated, it provides an easy place
to document various kernel API changes, with the corresponding
implementations in vg_syscalls.c.

For example, on Linux, we'd have something like this:

vg_syscall.h:
#define VKI_SC_exit    __NR_exit
#define VKI_SC_getpid __NR_getpid

And on FreeBSD, we'd have something like this:

#define VKI_SC_exit     SYS_exit
#define VKI_SC_getpid    SYS_getpid

2) Introduce a mapping layer for pthread structures

Currently the vg_libpthread.c code assumes the names of pthread_mutex
structure elements.  As expected, these are not the same on FreeBSD and are
likely different on the other *BSDs as well.

I propose that we introduce some mapping #defines in vg_kerneliface.h to
handle such differences.

For example, on Linux:

#define VKI_PTHREAD_OWNER    __m_owner
#define VKI_PTHREAD_COUNT    __m_count
#define VKI_PTHREAD_KIND        __m_kind

And on FreeBSD:

#define VKI_PTHREAD_OWNER    m_owner
#define VKI_PTHREAD_COUNT    m_data.m_count
#define VKI_PTHREAD_KIND        m_type

Then we can do things like this instead, which should be more portable:

int __pthread_mutex_init(pthread_mutex_t *mutex,
                         const  pthread_mutexattr_t *mutexattr)
{
   mutex->VKI_PTHREAD_COUNT = 0;
   mutex->VKI_PTHREAD_OWNER = (_pthread_descr)VG_INVALID_THREADID;
   mutex->VKI_PTHREAD_KIND  = PTHREAD_MUTEX_ERRORCHECK_NP;
   if (mutexattr)
      mutex->VKI_PTHREAD_KIND = mutexattr->__mutexkind;
   return 0;
}

Thanks,

--
Matt Emmerton