keepitupkitty / test-tls-initial-exec

A small testcase to reproduce libGL's use of "initial-exec" TLS variables

"initial-exec" TLS variables and dlopen(3)

Description

This test program reproduces how Mesa's and NVIDIA's libGL.so use static TLS variables, using the "initial-exec" model.

When libGL.so is dlopen()'d directly or indirectly, the application crashes on FreeBSD. This happens with Firefox and Mesa when the latter is built with --enable-glx-tls. Firefox dlopen()'s libxul.so which is linked to libGL.so. LD_PRELOAD'ing libGL.so works around the crash. This test program is here to help understand the issue and fix it.

How to build and test

$ make test

Two programs and a library are compiled:

• app-link, which is linked to libfoo.so;
• app-dlopen, who dlopen()'s libfoo.so;
• libfoo.so, a simple library with a TLS variable.

app-linked works fine and prints:

$ ./app-link
foo: 2016

app-dlopen segfaults.