On 2020-02-21 18:38, J.W. Jagersma wrote: > On 2020-02-19 00:16, Jim Wilson wrote: >> On Wed, Feb 12, 2020 at 9:10 AM J.W. Jagersma <jwjagersma@xxxxxxxxx> wrote: >>> i686-gcc -march=i386: cmov (!) >> >> Did you check to see where the cmov instruction is coming from? The >> compiler won't generate it with -march=i386, but there may be a >> precompiled library like libgcc or libstdc++ that contains the cmov >> instruction because they were compiled for i686. In order to get the >> right effect with -march=i386, you would need to build multiple copies >> of the libraries, one of them with -march=i386. We call this >> multilibs. This is normally done with -m32/-m64 so a single compiler >> can generate both 32-bit and 64-bit code, but it is not normally done >> with i386 and i686. You would have to change the default >> configuration to build multilibs based on -march. > > Say I wanted to do build multilibs for x86, where would I start? I've > been looking through the configure/make files but I don't see how it's > done. Nevermind that, I found it in the documentation here: https://gcc.gnu.org/onlinedocs/gccint/Target-Fragment.html
