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  1. Feb 05, 2014
    • Borislav Petkov's avatar
      x86: Disable generation of traditional x87 instructions · b399fe35
      Borislav Petkov authored
      
      
      We recently had the case where wrongly used floating-constant 'E' caused
      the generation of traditional x87 instructions in kernel code and
      wreaking all kinds of havoc.
      
      Disable the generation of those too. This will save people a lot of time
      when trying to debug such issues by erroring out of the build instead of
      let them manifest themselves in very spectacular and happy-crappy ways
      at runtime.
      
      We're using -mno-fp-ret-in-387 in addition to -mno-80387 (which is ==
      -msoft-float) because, as the gcc manpage says:
      
        On machines where a function returns floating-point results in the
        80387 register stack, some floating-point opcodes may be emitted even
        if -msoft-float is used.
      
      so we want to turn off *all* non-integer instructions involving any
      architectural FPU state, unless it is absolutely necessary (and those
      cases need special handling anyway).
      
      Cc: Jiri Kosina <jkosina@suse.cz>
      Cc: Michael Matz <matz@suse.de>
      Cc: Michal Hocko <mhocko@suse.cz>
      Signed-off-by: default avatarBorislav Petkov <bp@suse.de>
      Link: http://lkml.kernel.org/r/1391561711-3023-1-git-send-email-bp@alien8.de
      
      
      Signed-off-by: default avatarH. Peter Anvin <hpa@zytor.com>
      b399fe35
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