gcc49: bug in libstdc++ when using std::complex

[vsoftco@…]

The following produces a segfault when compiling with g++4.9.1 using libstdc++ that comes with it.

#include <complex>
#include <iostream>

int main()
{
	std::complex<double> a{1,0};
	std::cout << a.imag() << std::endl; // works fine
	std::cout << a << std::endl; // segfault
}

Probably there is something related to ostream operator<< overloading for std::complex, although I cannot say for sure. However, the bug is extremely important, as it makes the whole std::complex part of the library unusable.

[ryandesign (Ryan Carsten Schmidt)]

You should probably test if the problem remains in gcc5, and also report the problem to the developers of gcc. All we do at MacPorts is package the software they provide.

[larryv (Lawrence Velázquez)]

I can reproduce the segfault.

[vsoftco@…]

Replying to ryandesign@…:

You should probably test if the problem remains in gcc5, and also report the problem to the developers of gcc. All we do at MacPorts is package the software they provide.

I tested the code with gcc4.9.1 from Homebrew (and using its libstdc++), and there is no segfault. I have also filled a bug with gcc, however it seems extremely strange that one version of gcc4.9.1 works and another one not.

[larryv (Lawrence Velázquez)]

I know what’s going on. The crash log looks uncomfortably familiar…

Exception Type:        EXC_BAD_ACCESS (SIGSEGV)
Exception Codes:       EXC_I386_GPFLT

Thread 0 Crashed:: Dispatch queue: com.apple.main-thread
0   libdyld.dylib                 	0x00007fff82b01432 stack_not_16_byte_aligned_error + 0

…because this is my old friend, the Libtool MACOSX_DEPLOYMENT_TARGET bug.

I’ve attached a preliminary patch​. Could you try it?

% sudo port uninstall libgcc gcc49 && sudo port clean libgcc gcc49
% sudo port patch libgcc
% curl https://trac.macports.org/raw-attachment/ticket/45483/yosemite-symbol-lookup.patch | sudo patch -p1 -d $(port work libgcc)/gcc-4.9.1
% sudo port install libgcc
% sudo port patch gcc49
% curl https://trac.macports.org/raw-attachment/ticket/45483/yosemite-symbol-lookup.patch | sudo patch -p1 -d $(port work libgcc)/gcc-4.9.1
% sudo port install gcc49

[vsoftco@…]

Thanks, will try later today and let you know.

[larryv (Lawrence Velázquez)]

I’ve pushed the change in r127092. Can you run selfupdate and try the new version (4.9.1_1)?

[larryv (Lawrence Velázquez)]

Fixed gcc48 in r127093 and gcc5 in r127094.

[vsoftco@…]

It works, many thanks for the super fast fix!

[vsoftco@…]

I have a question, is the bug related to libgcc or to macports? If it's related to macports, I'll remove the bug I filled for g++. Thanks again for the great work in fixing it!

[larryv (Lawrence Velázquez)]

It’s an upstream bug. The configure scripts in the distribution are based on the current Libtool, which ​uses incorrect linker flags when MACOSX_DEPLOYMENT_TARGET is set to “10.10”. We set that environment variable in our builds; Homebrew does not, which is why you didn’t observe the bug there.

Could you provide a link to the bug report you filed?

[larryv (Lawrence Velázquez)]

Upstream PR: ​https://gcc.gnu.org/bugzilla/show_bug.cgi?id=63610