#599 bad code generation (crash) related to va_args without frame pointer

[Brian Paul]

Hi, we use mingw-64 to build (cross-compile) Mesa (the OpenGL work-alike) for Windows on Linux. With mingw-w64 versions 5.3.1 and 6.2.0 (at least) bad code is generated in one of the Mesa source files. This leads to semi-random crashes when running OpenGL apps on Windows.

My coworker, Jose, and I have narrowed it down to a Mesa source file that uses variable arguments. A test case is attached. If we compile with -O2 or -O3 the crash occurs (it does not occur with -O0 or -O1). The crash is avoided with -O2 and -O3 if we also specify -fno-omit-frame-pointer.

I haven't yet managed to build mingw-w64 v5.0.1 so I don't know if the bug is still present in that version.

We have a work-around (compile the file in question with -O1) but it would great if this bug could be addressed for the future.

Thanks.

[Mateusz Mikuła]

At MSYS2 we are also having issues with native 32bit Mesa (64bit is fine): https://github.com/Alexpux/MINGW-packages/issues/2089
We couldn't find the reason but most likely that's it.

We use mingw-w64 build from git updated much more often than releases and GCC 6.3.0.

[pal100 rep0roc]

GCC 4.9 may be affected as well. I tested old GCC 4.9 builds from here:
https://sourceforge.net/projects/msys2/files/REPOS/MINGW_GCC_4_9/i686/
The oldest - 10.0.0 is not affected, but the newest 10.6.0 is.
What's interestingly different about 10.0.0 is that it was built without LLVM, so it only includes the very slowest softpipe driver.

[Ozkan Sezer]

Any progress with tis issue?

[Ozkan Sezer]

Has there been any progress with this issue?

Has this issue been reported to gcc? (assuming that it's a gcc bug)

[Mateusz Mikuła]

Probably fixed: https://github.com/Alexpux/MINGW-packages/issues/2089#issuecomment-361540645

[Jose Fonseca]

I just tried with i686-w64-mingw32-g++ 6.3.0 that's included with Ubuntu 17.10 and no longer can repro.

I'm not sure if the issue was truly fixed between 6.2.0 and 6.3.0, or is a fluke.

I didn't spot any pertinent bug fix on
https://gcc.gnu.org/bugzilla/buglist.cgi?bug_status=RESOLVED&resolution=FIXED&target_milestone=6.3