t-constants FAILs with GMP 6.2.1 on aarch64

[Richard Biener]

On Mon, 28 Dec 2020, Torbjörn Granlund wrote:

> [Sorry for the slow reply to your report!  I have been quite busy.]
> 
> I think I understand the problem, but how to fix it is not obvious to
> me.
> 
>   And GMP_ASM_RODATA likely arrives at the .text result since CFLAGS
>   includes -flto.  Is there any reason to use CFLAGS in those tests?
> 
> It is common that CFLAGS affect the ABI and as a result the way things
> are defined in asm.
> 
>   The other tests seem to just switch on target systems or use
>   TRY_ASSEMBLE - that looks less fragile to me.
> 
> TRY_ASSEMBLE might not work too well with C snippets which we need to
> use in GMP_ASM_RODATA.  :-)
> 
>   Defaulting to .text on aarch64 when using GOT relocations in asm
>   is probably asking for trouble (see my case), I think the test
>   should fail when running into
> 
>     else
>       echo "Couldn't find label: 
>   ^${tmp_gsym_prefix}foo$gmp_cv_asm_label_suffix" >&AC_FD_CC
> 
>   rather than falling back to .text.  Alternatively all targets that
>   use explicit references to [RO]DATA should have a safer default.
> 
> For some platforms, the correct segment for RODATA is .text.
> 
>   What's the collection of RODATA results "supported"?  As said a
>   switch like for GMP_ASM_GLOBL looks less error-prone here.
> 
> Perhaps, but hardwiring things is against the spirit of autoconf and
> creates a maintenance burden.
> 
> The syntax for rodata varies for between arm64 platforms.

Hmm, OK.  A simpler(?) alternative might be to check for
compiler support of -fno-lto and unconditionally append that
to CFLAGS for this (or all) configure test(s)?

Richard.

-- 
Richard Biener <rguenther at suse.de>
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