Segfault when replaying on master

[emberian]

With this trace, ./glretrace texture.trace segfaults, with the following backtrace:

#0  0x0000000000470aad in glws::Context::hasExtension (this=0xa25090, string=0x652321 "GL_ARB_timer_query")
    at /home/cmr/src/apitrace/retrace/glws.cpp:100
#1  0x000000000042d34a in glretrace::Context::hasExtension (this=0xa250f0, extension=0x652321 "GL_ARB_timer_query")
    at /home/cmr/src/apitrace/retrace/glretrace.hpp:57
#2  0x000000000042cbfe in glretrace::initContext () at /home/cmr/src/apitrace/retrace/glretrace_main.cpp:294
#3  0x000000000042de75 in glretrace::makeCurrent (call=..., drawable=0xa25030, context=0xa250f0)
    at /home/cmr/src/apitrace/retrace/glretrace_ws.cpp:176
#4  0x00000000005e8e45 in retrace_glXMakeCurrent (call=...) at /home/cmr/src/apitrace/retrace/glretrace_glx.cpp:148
#5  0x000000000042a05d in retrace::Retracer::retrace (this=0x901ce0 <retracer>, call=...) at /home/cmr/src/apitrace/retrace/retrace.cpp:119
#6  0x000000000041f93a in retrace::retraceCall (call=0x9df770) at /home/cmr/src/apitrace/retrace/retrace_main.cpp:184
#7  0x0000000000421802 in retrace::RelayRunner::runLeg (this=0x9df630, call=0x9df770) at /home/cmr/src/apitrace/retrace/retrace_main.cpp:335
#8  0x00000000004216f4 in retrace::RelayRunner::runRace (this=0x9df630) at /home/cmr/src/apitrace/retrace/retrace_main.cpp:306 
#9  0x000000000041fc8a in retrace::RelayRace::run (this=0x7fffffffd160) at /home/cmr/src/apitrace/retrace/retrace_main.cpp:473
#10 0x000000000041fe59 in retrace::mainLoop () at /home/cmr/src/apitrace/retrace/retrace_main.cpp:533
#11 0x00000000004205e0 in main (argc=3, argv=0x7fffffffd368) at /home/cmr/src/apitrace/retrace/retrace_main.cpp:794

Poking around a bit, it's a NULL pointer. glGetString(GL_EXTENSIONS) is returning NULL, and glGetError is GL_INVALID_ENUM. According to a bisection, @jrfonseca broke it with:

[984010aac97b628d390dce6fecb8197eadfabb47] glretrace: Support more profiles; match the profile used in glXCreateContextAttribsARBG call.

So it looks like context creation is broken, at least for GL 3.1. I don't really know how to fix it or what the error is.

[jrfonseca]

Thanks for the detailed error report.

The issue was that when we request OpenGL 3.1 in glretrace there is no guarantee we get a compatibility context (with Mesa we don't), and glGetString(GL_EXTENSIONS) only works for compatibility contexts. I knew about this but I got confused with the "core" profiles introduced in OpenGL 3.2 and higher.

I've fixed this now.