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Re: [libitm] Check if GCC uses assembler cfi support


Richard Henderson <rth@redhat.com> writes:

> On 04/07/2014 04:33 AM, Rainer Orth wrote:
>> The patch allowed i386-pc-solaris2.11 bootstraps to finish without
>> regressions on trunk and 4.8 branch, still need to test 4.7 branch.
>> 
>> Ok for trunk, 4.8 and 4.7 branches once testing completes?
>> 
>> 	Rainer
>> 
>> 
>> 2014-04-07  Rainer Orth  <ro@CeBiTec.Uni-Bielefeld.DE>
>> 
>> 	* config/generic/asmcfi.h: Also check for
>> 	__GCC_HAVE_DWARF2_CFI_ASM.
>
> Looks fine.

Testing was fine on i386-pc-solaris2.11 with /bin/as on trunk, 4.8 and
4.7 branches, as well as x86_64-unknown-linux-gnu.

However, i386-pc-solaris2.11 with gas was confusing at first: for the
32-bit PIC case, no .eh_frame was generated.  It turned out this happens
because in this case config/i386/sol2.h (ASM_PREFERRED_EH_DATA_FORMAT)
is a lie: it claims datarel encoding for the 32-bit PIC case.  This way,
dwarf2out_do_cfi_asm returns false and c-family/c-cppbuiltin.c
(c_cpp_builtins) doesn't define __GCC_HAVE_DWARF2_CFI_ASM.

In fact, gas with cfi directives uses pcrel encoding, thus
__GCC_HAVE_DWARF2_CFI_ASM should be defined.

ISTM that the ASM_PREFERRED_EH_DATA_FORMAT redefinition above should be
wrapped in HAVE_AS_IX86_DIFF_SECT_DELTA, but I'm quite reluctant to make
such a change so late in the 4.9 release cycle.

I'll certainly try it post-4.9, especially given that Solaris 9 support
will be removed by then and current Solaris 10 and 11 assemblers *can*
subtract symbols in different sections.

Unless I'm missing something, I'm thus going to check in the patch as is
within a day.  I believe that losing unwind info in a single case here
is worth avoiding the bootstrap failure.

	Rainer

-- 
-----------------------------------------------------------------------------
Rainer Orth, Center for Biotechnology, Bielefeld University


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