COFF_TYPE on x86_64

[Jeremy Drake]

On msys2's MINGW-packages, we recently hit an issue[1] which I eventually
tracked down to the very issue documented in
https://gmplib.org/repo/gmp-6.2/file/09e101b6f2ff/acinclude.m4#l2128

> > My current theory is that for some unknown reason, gmp's assembly
> > functions are resulting in symbols that bfd believes are data, not
> > functions. Without dllimport, this is causing it to use the
> > auto-import hack, which has the Windows loader modify addresses in the
> > function itself, rather than using the jmp thunk which references the
> > `__imp_` symbol. This cannot work correctly on x64 with large
> > addresses, because the CALL instruction is taking a 32-bit relative
> > operand. The only way this can work is with a jmp thunk (unless the
> > compiler knew to generate an indirect CALL, which is what dllimport
> > does).
>
> The 'unknown reason' I mentioned is that the functions were lacking
> `.type 32`.
>
> > gmp's configure script checks for support for .type pseudo-op, but on
> > mingw that is only allowed inside a .def, and must take an integer not
> > `@function`, so gmp suppresses it altogether.

Strangely, the fix for this was only applied to x86, and not x86_64.  This
patch applies the fix to x86_64.

[1]: https://github.com/msys2/MINGW-packages/issues/6983
-------------- next part --------------
--- gmp-6.2.0/mpn/x86_64/x86_64-defs.m4.orig	2020-10-01 22:00:35.891856900 -0700
+++ gmp-6.2.0/mpn/x86_64/x86_64-defs.m4	2020-10-01 22:01:29.579372600 -0700
@@ -93,10 +93,28 @@
 m4_assert_numargs(1)
 `	GLOBL	$1
 	TYPE($1,`function')
+	COFF_TYPE($1)
 $1:
 ')
 
 
+dnl  Usage: COFF_TYPE(GSYM_PREFIX`'foo)
+dnl
+dnl  Emit COFF style ".def ... .endef" type information for a function, when
+dnl  supported.  The argument should include any GSYM_PREFIX.
+dnl
+dnl  See autoconf macro GMP_ASM_COFF_TYPE for HAVE_COFF_TYPE.
+
+define(COFF_TYPE,
+m4_assert_numargs(1)
+m4_assert_defined(`HAVE_COFF_TYPE')
+`ifelse(HAVE_COFF_TYPE,yes,
+	`.def	$1
+	.scl	2
+	.type	32
+	.endef')')
+
+
 dnl  Usage: ASSERT([cond][,instructions])
 dnl
 dnl  If WANT_ASSERT is 1, output the given instructions and expect the given
--- gmp-6.2.0/configure.ac.orig	2020-10-01 22:24:41.048101000 -0700
+++ gmp-6.2.0/configure.ac	2020-10-01 22:24:56.657479600 -0700
@@ -3792,6 +3792,7 @@
         64|x32)
           GMP_INCLUDE_MPN(x86_64/x86_64-defs.m4)
           AC_DEFINE(HAVE_HOST_CPU_FAMILY_x86_64)
+          GMP_ASM_COFF_TYPE
 	  case $host in
 	    *-*-darwin*)
 	      GMP_INCLUDE_MPN(x86_64/darwin.m4) ;;