Gentoo Archives: gentoo-amd64

From: Frank Peters <frank.peters@×××××××.net>
To: gentoo-amd64@l.g.o
Subject: Re: [gentoo-amd64] Re: GCC-4.5.2 Has Serious Problems
Date: Fri, 01 Jul 2011 05:24:14
In Reply to: Re: [gentoo-amd64] Re: GCC-4.5.2 Has Serious Problems by Mark Knecht
On Thu, 30 Jun 2011 21:36:38 -0700
Mark Knecht <markknecht@×××××.com> wrote:

> > I think it's completely appropriate for this list. This distro expects > that we put CFLAG options in make.conf so I need to hear about this > stuff even if I don't have to background to completely understand > what's really causing the problem. >
In this case, or in the case of any program where "-fno-strict-aliasing" could make a difference, the maintainer of the program would include the option in the ebuild. The user would not have to worry too much about it. But yes, it is always good to know about the compiler flags. To see exactly what compile flags are being used in your programs, here is a neat method I picked up from somewhere. Just open a terminal and enter the following command: echo 'int main(){return 0;}' > test.c && gcc -v -Q $CFLAGS test.c -o test && rm test.c test In place of $CFLAGS just substitute any option of interest. There will be a flood of output, but just scroll back a few lines to find the "options passed:" and "options enabled:" sections. For example, using "-O2" for $CFLAGS indicates that "-fstrict-aliasing" is used, but it is not used with "-O1." It also shows that with "-O2" the option "-mno-sse4" is used, and so if you want to use SSE4 for certain programs (e.g. video, audio) you will need to specifically enable it. There may be an even slicker way to reveal the flags, but this is the only way I know. Frank Peters