https://gcc.gnu.org/bugzilla/show_bug.cgi?id=66458
kargl at gcc dot gnu.org changed:
What |Removed |Added
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CC| |kargl at gcc dot gnu.org
--- Comment #3 from kargl at gcc dot gnu.org ---
(In reply to Jan van Dijk from comment #0)
> It appears that the mere act of loading libgfortran.so changes the FPU
> exception mask. It looks as if the library contains initialization code that
> I would have expected to appear in the program's start-up code. (Indeed it
> appears to do so in line 266 of libgfortran/runtime/main.c.)
>
> The problem can be reproduced by compiling the following C program:
>
> // fpuflags
> #include <fenv.h>
> #include <dlfcn.h>
#pragma STDC FENV_ACCESS ON
> int main(int argc, char* argv[])
> {
> volatile double d=0;
fenv_t fpu;
> feenableexcept(FE_ALL_EXCEPT);
> if (argc==2)
> {
fegetenv(&fpu);
> dlopen(argv[1],RTLD_NOW);
fesetenv(&fpu);
> }
> // I expect the expression 1/d to generate an FPU exception:
> return 1/d;
> }
>
> > gcc fpuflags.c -ldl -lm
> > ./a.out
> Floating point exception
> > ./a.out /usr/lib64/libstdc++.so.6
> Floating point exception
> > ./a.out /usr/lib64/gcc/x86_64-suse-linux/4.8/libgfortran.so
> > #nothing happens
>
> After merely loading libgfortan.so, no FPU exceptions are generated anymore.
> Loading libstdc++.so does not result in such problem.
>
> This is a problem in my numerical application where libgfortran.so is loaded
> as a depency of a plugin library that is loaded at runtime.
You're loading a dynamic library that has a constructor that is
executed to set up the library's internal state. If you're loading
libraries and you want a specific FPU state, then you'll need to
save and reset the state.
--
steve
