Re: [Valgrind-users] Need support in debugging Valgrind 3.18 glibc segv error

[John R. <jr...@bi...>]

On 4/14/25 7:13 AM, kiran hardas wrote:
> Hi Team,
> 
> I haven't received any suggestion or advice to my shmat valgrind wrapper 
> behaviour mentioned in previous mail.

> --- a/valgrind/coregrind/m_syswrap/syswrap-generic.c
> +++ b/valgrind/coregrind/m_syswrap/syswrap-generic.c
> @@ -2052,7 +2052,7 @@ ML_(generic_PRE_sys_shmat) ( ThreadId tid,
>   {
>      /* void *shmat(int shmid, const void *shmaddr, int shmflg); */
>      SizeT  segmentSize = get_shm_size ( arg0 );
> -   UWord tmp;
> +   UWord tmp = 0;
>      Bool  ok;
>      if (arg1 == 0) {
>         /* arm-linux only: work around the fact that

In the current git source for 
valgrind/coregrind/m_syswrap/syswrap-generic.c at function 
ML_(generic_PRE_sys_shmat) (line 2346), I see
=====
    if (arg1 == 0) {
       /* arm-linux only: work around the fact that
          VG_(am_get_advisory_client_simple) produces something that is
          VKI_PAGE_SIZE aligned, whereas what we want is something
          VKI_SHMLBA aligned, and VKI_SHMLBA >= VKI_PAGE_SIZE.  Hence
          increase the request size by VKI_SHMLBA - VKI_PAGE_SIZE and
          then round the result up to the next VKI_SHMLBA boundary.
          See bug 222545 comment 15.  So far, arm-linux is the only
          platform where this is known to be necessary. */
=====
where "git blame" for the first two lines says
=====
cc8ccbbfb4 coregrind/m_syswrap/syswrap-generic.c   (Julian Seward 
2005-09-27 19:20:21 +0000 2346)    if (arg1 == 0) {
566a25cf7e coregrind/m_syswrap/syswrap-generic.c   (Julian Seward 
2010-10-06 15:24:39 +0000 2347)       /* arm-linux only: work around the 
fact that
=====
but I do not see any guard that tests for arm-linux only.  So I would
say that the current source has a bug!

Thus your change
> With this change, my shmat functions calls are working fine as different adresses are picked up for attach.

is not only OK; it should be propagated into the official source.