[Bug 1757517] [NEW] An unused thread-local memory allocation can cause library calls to segfault.

[Moosfet]

Public bug reported:

I've discovered that adding "static __thread anything[8 * 1048576]" to
otherwise working programs will cause them to segfault.  I've attached a
short example that demonstrates the problem.

Compile the attached program like this:  gcc -o test test.c -lpthread
-lasound

When running it, it will display this:

Spawning thread...
Joining thread...
I'm a thread!
Segmentation fault

Unfortunately I haven't been able to figure out how to reproduce it
without using libasound, except that I can use libjack to trigger it
instead, but since that makes two independent libraries that have this
problem, I assume it is caused by something common between them, like
pthreads, GCC, or the Linux kernel.

FWIW, with the Jack version of the bug, I've seen it do two things.
With a larger allocation it displays messages about being unable to
create threads before failing to connect to its server.  With a smaller
allocation, it connects to its server, but then segfaults later in a
different call to libjack.

In all cases, merely removing the "static __thread anything[8 *
1048576]" from the program causes the libraries to work correctly.
Since the variable is never accessed by anything, adding it to the
programs should have no effect.

** Affects: glibc (Ubuntu)
     Importance: Undecided
         Status: New

** Attachment added: "Short example demonstrating the problem."
   https://bugs.launchpad.net/bugs/1757517/+attachment/5086214/+files/test.c

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https://bugs.launchpad.net/bugs/1757517

Title:
  An unused thread-local memory allocation can cause library calls to
  segfault.

Status in glibc package in Ubuntu:
  New

Bug description:
  I've discovered that adding "static __thread anything[8 * 1048576]" to
  otherwise working programs will cause them to segfault.  I've attached
  a short example that demonstrates the problem.

  Compile the attached program like this:  gcc -o test test.c -lpthread
  -lasound

  When running it, it will display this:

  Spawning thread...
  Joining thread...
  I'm a thread!
  Segmentation fault

  Unfortunately I haven't been able to figure out how to reproduce it
  without using libasound, except that I can use libjack to trigger it
  instead, but since that makes two independent libraries that have this
  problem, I assume it is caused by something common between them, like
  pthreads, GCC, or the Linux kernel.

  FWIW, with the Jack version of the bug, I've seen it do two things.
  With a larger allocation it displays messages about being unable to
  create threads before failing to connect to its server.  With a
  smaller allocation, it connects to its server, but then segfaults
  later in a different call to libjack.

  In all cases, merely removing the "static __thread anything[8 *
  1048576]" from the program causes the libraries to work correctly.
  Since the variable is never accessed by anything, adding it to the
  programs should have no effect.

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