[Buildroot] [PATCH] mbedtls: fix x86 PIC build with GCC < 5
Peter Korsgaard
peter at korsgaard.com
Tue Aug 28 07:54:05 UTC 2018
>>>>> "Peter" == Peter Korsgaard <peter at korsgaard.com> writes:
> Fixes:
> http://autobuild.buildroot.net/results/d6d/d6dc9a640aa1f6650a3e7b9397f2fe2ae3433f4d/
> http://autobuild.buildroot.net/results/ab5/ab5a58ea7845f9f378454ee1aa7e872448618ba9/
> ebx was recently added to the x86 inline asm MULADDC_STOP clobber list to
> fix #1550, but this causes the build to fail with GCC < 5 when building in
> PIC mode with errors like:
> include/mbedtls/bn_mul.h:46:13: error: PIC register clobbered by ‘ebx’ in ‘asm’
> This is because older GCC versions treated the x86 ebx register (which is
> used for the GOT) as a fixed reserved register when building as PIC.
> This is fixed by an improved register allocator in GCC 5+. From the release
> notes:
> Register allocation improvements: Reuse of the PIC hard register, instead of
> using a fixed register, was implemented on x86/x86-64 targets. This
> improves generated PIC code performance as more hard registers can be used.
> https://www.gnu.org/software/gcc/gcc-5/changes.html
> As a workaround, add a patch to detect this situation and disable the inline
> assembly, similar to the MULADDC_CANNOT_USE_R7 logic.
> Patch submitted upstream: https://github.com/ARMmbed/mbedtls/pull/1986
> Signed-off-by: Peter Korsgaard <peter at korsgaard.com>
Committed, thanks.
--
Bye, Peter Korsgaard
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