t-constants FAILs with GMP 6.2.1 on aarch64

[Richard Biener]

On Wed, 9 Dec 2020, Richard Biener wrote:

> 
> See https://bugzilla.opensuse.org/show_bug.cgi?id=1179751 where
> Guillaume tracked this down to a change from GMP 6.2.0 to GMP 6.2.1.
> 
> The issue shows up as
> 
> Starting program: /home/abuild/rpmbuild/BUILD/gmp-6.2.1/tests/t-constants 
> Missing separate debuginfos, use: zypper install 
> glibc-debuginfo-2.32-3.3.aarch64
> PP_INVERTED == 21cfe6cfc938b36b, but pp_inverted_calc == 20f8c8b59d4cb9bc
> 
> Reverting
> 
> diff --git a/mpn/arm64/invert_limb.asm b/mpn/arm64/invert_limb.asm
> index a94b0e961..6a99bf002 100644
> --- a/mpn/arm64/invert_limb.asm
> +++ b/mpn/arm64/invert_limb.asm
> @@ -41,9 +41,9 @@ C Compiler generated, mildly edited.  Could surely be 
> further optimised.
>  ASM_START()
>  PROLOGUE(mpn_invert_limb)
>         lsr     x2, x0, #54
> -       adrp    x1, approx_tab
> +       LEA_HI( x1, approx_tab)
>         and     x2, x2, #0x1fe
> -       add     x1, x1, :lo12:approx_tab
> +       LEA_LO( x1, approx_tab)
>         ldrh    w3, [x1,x2]
>         lsr     x4, x0, #24
>         add     x4, x4, #1
> 
> fixes the issue.  Disassembly of the bogus libgmp routine is 
> (via objdump)
> 
> 000000000005d188 <__gmpn_invert_limb>:
>    5d188:       d376fc02        lsr     x2, x0, #54
>    5d18c:       d0000181        adrp    x1, 8f000 
> <toom_eval_pm2exp.c.32b029f3+0x1d9>
>    5d190:       927f1c42        and     x2, x2, #0x1fe
>    5d194:       f9475c21        ldr     x1, [x1, #3768]
>    5d198:       78626823        ldrh    w3, [x1, x2]
>    5d19c:       d358fc04        lsr     x4, x0, #24
>    5d1a0:       91000484        add     x4, x4, #0x1
> 
> relocations of the object are
> 
> Relocation section '.rela.text' at offset 0x558 contains 2 entries:
>   Offset          Info           Type           Sym. Value    Sym. Name + 
> Addend
> 000000000004  000100000137 R_AARCH64_ADR_GOT 0000000000000000 .text + 7c
> 00000000000c  000100000138 R_AARCH64_LD64_GO 0000000000000000 .text + 7c
> 
> not sure what goes wrong, but the approx_tab data ends up in the .text
> section (so going via the GOT is even unnecessary - but I see the .asm
> file uses .DATA which hints at that it should go to .data or .rodata).

Btw, my config.m4 is the following which explains why I get approx_tab
in .text (and I guess a GOT relocation then simply invokes undefined
behavior?)

And GMP_ASM_RODATA likely arrives at the .text result since CFLAGS
includes -flto.  Is there any reason to use CFLAGS in those tests?
The other tests seem to just switch on target systems or use
TRY_ASSEMBLE - that looks less fragile to me.

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.

What's the collection of RODATA results "supported"?  As said a
switch like for GMP_ASM_GLOBL looks less error-prone here.

Richard.

dnl config.m4.  Generated automatically by configure.
changequote(<,>)                                                                
ifdef(<__CONFIG_M4_INCLUDED__>,,<
define(<CONFIG_TOP_SRCDIR>,<`../.'>)                                            
define(<WANT_ASSERT>,0)
define(<WANT_PROFILING>,<`no'>)                                                 
define(<M4WRAP_SPURIOUS>,<no>)
define(<TEXT>, <.text>)                                                         
define(<DATA>, <.data>)
define(<LABEL_SUFFIX>, <:>)                                                     
define(<GLOBL>, <.globl>)
define(<GLOBL_ATTR>, <>)                                                        
define(<GSYM_PREFIX>, <>)
define(<RODATA>, <.text>)                                                       
define(<TYPE>, <.type   $1,@$2>)
define(<SIZE>, <.size   $1,$2>)                                                 
define(<LSYM_PREFIX>, <.L>)
define(<W32>, <.long>)                                                          
define(<ALIGN_LOGARITHMIC>,<yes>)
define(<SQR_TOOM2_THRESHOLD>,<18>)                                              
define(<BMOD_1_TO_MOD_1_THRESHOLD>,<40>)
define(<SIZEOF_UNSIGNED>,<4>)                                                   
define(<GMP_LIMB_BITS>,64)
define(<GMP_NAIL_BITS>,0)                                                       
define(<GMP_NUMB_BITS>,eval(GMP_LIMB_BITS-GMP_NAIL_BITS))
>)                                                                              
changequote(`,')
ifdef(`__CONFIG_M4_INCLUDED__',,`                                               
include(CONFIG_TOP_SRCDIR`/mpn/asm-defs.m4')
include_mpn(`arm64/arm64-defs.m4')                                              
define_not_for_expansion(`HAVE_HOST_CPU_aarch64')
define_not_for_expansion(`HAVE_ABI_64')                                         
define_not_for_expansion(`HAVE_LIMB_LITTLE_ENDIAN')
define_not_for_expansion(`HAVE_DOUBLE_IEEE_LITTLE_ENDIAN')                      
')            
define(`__CONFIG_M4_INCLUDED__')