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On Thu, 30 Jun 2011 21:36:38 -0700 |
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Mark Knecht <markknecht@×××××.com> wrote: |
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> |
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> I think it's completely appropriate for this list. This distro expects |
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> that we put CFLAG options in make.conf so I need to hear about this |
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> stuff even if I don't have to background to completely understand |
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> what's really causing the problem. |
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> |
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In this case, or in the case of any program where "-fno-strict-aliasing" |
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could make a difference, the maintainer of the program would include |
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the option in the ebuild. The user would not have to worry too much |
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about it. |
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But yes, it is always good to know about the compiler flags. |
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To see exactly what compile flags are being used in your programs, here |
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is a neat method I picked up from somewhere. Just open a terminal and |
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enter the following command: |
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echo 'int main(){return 0;}' > test.c && gcc -v -Q $CFLAGS test.c -o test && rm test.c test |
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In place of $CFLAGS just substitute any option of interest. There will |
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be a flood of output, but just scroll back a few lines to find the "options |
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passed:" and "options enabled:" sections. |
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For example, using "-O2" for $CFLAGS indicates that "-fstrict-aliasing" is |
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used, but it is not used with "-O1." |
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It also shows that with "-O2" the option "-mno-sse4" is used, and so if |
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you want to use SSE4 for certain programs (e.g. video, audio) you will |
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need to specifically enable it. |
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There may be an even slicker way to reveal the flags, but this is the |
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only way I know. |
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Frank Peters |
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