new module 'rand'

[Bruno Haible]

On CheriBSD, I see these test failures:

FAIL: test-pthread-tss
FAIL: test-thread_local
FAIL: test-tls
FAIL: test-tss

In the debugger I see this:

(gdb) where
#0  random_r (estate=0x42319000 [rwRW,0x42319000-0x423190d0])
    at 
/local/scratch/jenkins/workspace/CheriBSD-pipeline_releng_22.12@2/cheribsd/lib/libc/stdlib/random.c:471
#1  0x0000000040394578 in rand () at 
/local/scratch/jenkins/workspace/CheriBSD-pipeline_releng_22.12@2/cheribsd/lib/libc/stdlib/rand.c:85
#2  0x0000000000111468 in perhaps_yield () at 
../../gltests/test-thread_local.c:79
#3  0x00000000001113dc in worker_thread (arg=0x8) at 
../../gltests/test-thread_local.c:127
#4  0x00000000401a19d4 in thrd_entry (arg=<optimized out>)
    at 
/local/scratch/jenkins/workspace/CheriBSD-pipeline_releng_22.12@2/cheribsd/lib/libstdthreads/thrd.c:52
#5  0x00000000401e3de4 in thread_start (curthread=0x408f4a00 
[rwRW,0x408f4a00-0x408f53d0])
    at 
/local/scratch/jenkins/workspace/CheriBSD-pipeline_releng_22.12@2/cheribsd/lib/libthr/thread/thr_create.c:319
#6  0x00000000401e38ec in _pthread_create (thread=0xfffffff7fe90 
[rwRW,0xfffffff7fe10-0xfffffff7ff10], attr=<optimized out>, 
start_routine=<optimized out>, 
    arg=<optimized out>) at 
/local/scratch/jenkins/workspace/CheriBSD-pipeline_releng_22.12@2/cheribsd/lib/libthr/thread/thr_create.c:214

(gdb) info locals
r = 0x423190d0 [rwRW,0x42319000-0x423190d0]
f = 0x42319054 [rwRW,0x42319000-0x423190d0]
i = <optimized out>

So, rand() is crashing in multithreaded tests. But it works fine in the many
single-threaded test programs. Could it be that rand() is not multithread-
safe?

According to the standards, rand() should be multithread-safe.

When I add a 'rand' module and force it to invoke the gnulib implementation
of random_r (via random()), I see a crash inside gnulib's random_r instead.
But wait! That's because gnulib's 'random' implementation is also not
multithread-safe:

  #ifdef _LIBC
  # include <libc-lock.h>
  #else
  /* Allow memory races; that's random enough.  */
  # define __libc_lock_define_initialized(class, name)
  # define __libc_lock_lock(name) ((void) 0)
  # define __libc_lock_unlock(name) ((void) 0)
  #endif

Memory races are not "random"; they are undefined behaviour. They crash on
CheriBSD and they may crash (or return low-quality random numbers) on other
systems as well.

With the patches below, rand() becomes multithread-safe, and the 4 test failures
disappear.


2023-11-09  Bruno Haible  <bruno@clisp.org>

        rand: Add tests.
        * tests/test-rand.c: New file.
        * modules/rand-tests: New file.

        rand: New module.
        * lib/rand.c: New file, based on glibc/stdlib/rand.c.
        * m4/rand.m4: New file.
        * modules/rand: New file.
        * doc/posix-functions/rand.texi: Mention the new module.

2023-11-09  Bruno Haible  <bruno@clisp.org>

        random: Fix multithread-safety bug on CheriBSD.
        * m4/random.m4 (gl_FUNC_RANDOM): Override on CheriBSD.
        * lib/random.c: Include glthread/lock.h.
        (__libc_lock_define_initialized, __libc_lock_lock, __libc_lock_unlock):
        Define to do real locking.
        * modules/random (Depends-on): Add lock.
        * doc/posix-functions/random.texi: Mention the multithread-safety
        problem.

0001-random-Fix-multithread-safety-bug-on-CheriBSD.patch
Description: Text Data

0002-rand-New-module.patch
Description: Text Data

0003-rand-Add-tests.patch
Description: Text Data