https://gcc.gnu.org/bugzilla/show_bug.cgi?id=104713
James Addison <jay+g...@jp-hosting.net> changed:
What |Removed |Added
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CC| |jay+g...@jp-hosting.net
--- Comment #5 from James Addison <jay+g...@jp-hosting.net> ---
Adrian wrote:
> To support the Geode in OLPC, the toolchain definition of i686 does include
> CMOV but it does not include multi-byte NOPs.
...
> Sorry for being unclear, this is the historical reason why the binutils/gcc
> definition of i686 does not include multi-byte NOPs.
Jakub wrote:
> Just build for those as -march=i586. preventing -fcf-protection with
> -march=i686 would be a really bad idea, that would basically prevent all of
> CET protection for 32-bit code, i686 is what is used as the supported lowest
> common denominator of 32-bit code.
Could the findings indicate that there are two bugs here?
- The Geode LX target capable of supporting fcf-protection but GCC-11
currently rejects that architecture and flag combination (in the
potentially-buggy code[1] that Adrian refers to)
- Multi-byte NOPs are emitted for architecture i686 by GCC-11, despite some
CPUs within that architecture lacking[2] support
Also potentially relevant is bug 41989.
[1] -
https://gcc.gnu.org/git/?p=gcc.git;a=blob;f=gcc/config/i386/i386-options.cc;h=805539364108eee07f5bda527acd6f39f3f7bf95;hb=HEAD#l2929
[2] - https://bugzilla.redhat.com/show_bug.cgi?id=579838#c32
