building gmp-6.1 for s390 (31-bit) w/asm disabled failing with undefined sdiv_qrnnd

[Mike Frysinger]

On 09 Dec 2016 20:20, Torbjörn Granlund wrote:
> Mike Frysinger <vapier at gentoo.org> writes:
> 
>   now the __gmpn_udiv_w_sdiv symbol is exported based on the asm
>   configure flag.  mpfr will link against it if it's available,
>   and if you rebuild gmp w/asm disabled, then mpfr is left in a
>   broken state until it gets rebuilt.  this can be a problem when
>   gcc itself relies on gmp/mpfr now :).
>   
>   here's gmp-6.1.0 built w/--enable-asm:
>   $ readelf -sW /usr/lib/libgmp.so | grep udiv_w_sdiv
>      439: 00025538   366 FUNC    GLOBAL DEFAULT   10 __gmpn_udiv_w_sdiv
>   here it's built w/--disable-asm:
>   $ readelf -sW /usr/lib/libgmp.so | grep udiv_w_sdiv
>   <nothing>
> 
> I don't see a solution to this within GMP.
> 
> When other packages rely on reverse engineering of GMP's internals, then
> things such as this are bound to happen.

i don't think it's that simple

here's the mpfr build output:
$ s390-ibm-linux-gnu-gcc -std=gnu99 -DTIME_WITH_SYS_TIME=1 -DHAVE_INTTYPES_H=1 -DHAVE_STDINT_H=1 -DHAVE_LOCALE_H=1 -DHAVE_WCHAR_H=1 -DHAVE_STDARG=1 -DHAVE_SYS_TIME_H=1 -DHAVE_STRUCT_LCONV_DECIMAL_POINT=1 -DHAVE_STRUCT_LCONV_THOUSANDS_SEP=1 -DHAVE_ALLOCA_H=1 -DHAVE_STDINT_H=1 -DHAVE_VA_COPY=1 -DHAVE_SETLOCALE=1 -DHAVE_GETTIMEOFDAY=1 -DHAVE_LONG_LONG=1 -DHAVE_INTMAX_T=1 -DMPFR_HAVE_INTMAX_MAX=1 -DMPFR_HAVE_FESETROUND=1 -DHAVE_DENORMS=1 -DHAVE_SIGNEDZ=1 -DHAVE_ROUND=1 -DHAVE_TRUNC=1 -DHAVE_FLOOR=1 -DHAVE_CEIL=1 -DHAVE_NEARBYINT=1 -DHAVE_LDOUBLE_IEEE_QUAD_BIG=1 -DMPFR_USE_THREAD_SAFE=1 -DHAVE_CLOCK_GETTIME=1 -DLT_OBJDIR=\".libs/\" -DHAVE_ATTRIBUTE_MODE=1 -DHAVE___GMPN_ROOTREM=1 -DHAVE___GMPN_SBPI1_DIVAPPR_Q=1 -I. -Wall -Wmissing-prototypes -Wpointer-arith -O2 -pipe -march=z10 -c mulders.c -o mulders.o
mulders.c: In function ‘mpfr_divhigh_n_basecase’:
mulders.c:221:7: warning: implicit declaration of function ‘__gmpn_udiv_w_sdiv’ [-Wimplicit-function-declaration]
       invert_limb (dinv, d1);
       ^

let's look at the preprocessed output for that symbol:
static mp_limb_t
mpfr_divhigh_n_basecase (mpfr_limb_ptr qp, mpfr_limb_ptr np,
                         mpfr_limb_srcptr dp, mp_size_t n)
{
...
  if (n == 1)
    {
      do { mp_limb_t dummy; ((void) 0); do { UWtype __r; (dinv) = __gmpn_udiv_w_sdiv (&__r, ~(d1), ~(mp_limb_t)0, d1); (dummy) = __r; } while (0); } while (0);

mulders.c looks like:
static mp_limb_t
mpfr_divhigh_n_basecase (mpfr_limb_ptr qp, mpfr_limb_ptr np,
                         mpfr_limb_srcptr dp, mp_size_t n)
{
...
  if (n == 1)
    {
      invert_limb (dinv, d1);

invert_limb in mpfr-gmp.h looks like:
#undef invert_limb
#define invert_limb(invxl,xl)                             \
  do {                                                    \
    mp_limb_t dummy;                                      \
    MPFR_ASSERTD ((xl) != 0);                             \
    udiv_qrnnd (invxl, dummy, ~(xl), ~(mp_limb_t)0, xl);  \
  } while (0)

and udiv_qrnnd in mpfr-longlong.h looks like:
/* If the processor has no udiv_qrnnd but sdiv_qrnnd, go through
   __udiv_w_sdiv (defined in libgcc or elsewhere).  */
#if !defined (udiv_qrnnd) && defined (sdiv_qrnnd)
#define udiv_qrnnd(q, r, nh, nl, d) \
  do {									\
    UWtype __r;								\
    (q) = __MPN(udiv_w_sdiv) (&__r, nh, nl, d);				\
    (r) = __r;								\
  } while (0)
#endif

finally, __MPN comes from gmp's installed gmp.h header:
#ifndef __MPN
#define __MPN(x) __gmpn_##x
#endif

otherwise mpfr's mpfr-longlong.h's copy would have kicked in:
/* This is used to make sure no undesirable sharing between different libraries
   that use this file takes place.  */
#ifndef __MPN
#define __MPN(x) __##x
#endif

so attempting to share code has caused a collision to rise up.
-mike
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