Re: [Valgrind-users] shmat parameters are modified by valgrind

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

The code was mangled by posting in HTML.  Instead, use plain text (or an attachment,
if the mailing list allows them.)  I [attempt to] attach the code I used:
   -rw-rw-r--. 1 jreiser jreiser 3125 Aug 14 09:30 shmtest.c

On my system, /usr/include/linux/shm.h says:
-----
#define SHMMAX 0x2000000                 /* max shared seg size (bytes) */
#define SHMMIN 1                         /* min shared seg size (bytes) */
#define SHMMNI 4096                      /* max num of segs system wide */
#define SHMALL (SHMMAX/getpagesize()*(SHMMNI/16))
#define SHMSEG SHMMNI                    /* max shared segs per process */
-----
In particular, SHMMAX is only 32MiB, so several of the attempted shared segments
are too big.  My current actual parameters in
   $ cat /proc/sys/kernel/shmall
   $ cat /proc/sys/kernel/shmmax
   $ cat /proc/sys/kernel/shmmni
agree with the defaults that are in shm.h.


My test program works for me under valgrind-3.8.0 on Fedora 17 x86_64 in 64-bit mode.
   Linux host.domain 3.5.0-2.fc17.x86_64 #1 SMP Mon Jul 30 14:48:59 UTC 2012 x86_64 x86_64 x86_64 GNU/Linux
   gcc (GCC) 4.7.0 20120507 (Red Hat 4.7.0-5)
I [attempt to] attach the output that I get:
   -rw-rw-r--. 1 jreiser jreiser 9321 Aug 14 09:31 shmtest.out


To see the system calls that valgrind sees:
   valgrind --trace-syscalls=yes ...
Of course you can run that under strace, too, in order to verify
that valgrind actually does what it says it is doing:
   strace valgrind --trace-syscalls=yes ...
but it is tedious to read the output.

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