Comment 88 for bug 587186

It's true that Geode LX is not-quite i686 and we seem to be aware of some other places in which it is lacking (in addition to nopl).

This time around it does appear that the only problematic package we know about is glibc, so I'll focus on that case.

The reason that glibc is the only affected package is because glibc's build system checks if the assembler supports the "-mtune" option, and if so, when building for i686 it passes -mtune=i686.

Normally gcc does not pass -mtune or -march to the assembler (surprised me, too). But glibc explicitly checks if the assembler accepts it, and if so, it passes -Wa,-mtune=i686 to gcc, causing gcc to pass -mtune=i686 to the assembler. (the assembler's -march option remains unused)

Passing -mtune=i686 to the assembler causes nopl to be used. This indicates an assembler bug, because mtune should produce enhanced code for a certain arch without breaking compat, but in this case using nopl instructions *will* break compat. This is http://sourceware.org/bugzilla/show_bug.cgi?id=6957 (looks like the developer wants a test case before continuing, I'll try and come up with one now)