Re: [PATCH] libstdc++: Add _Float128 to_chars/from_chars support for x86, ia64 and ppc64le with glibc

[Jakub Jelinek <jakub@redhat.com>]

On Mon, Nov 07, 2022 at 05:48:42PM +0000, Jonathan Wakely wrote:
> On Mon, 7 Nov 2022 at 16:11, Joseph Myers <joseph@codesourcery.com> wrote:
> >
> > On Wed, 2 Nov 2022, Jakub Jelinek via Gcc-patches wrote:
> >
> > > APIs.  So that one can build gcc against older glibc and then compile
> > > user programs on newer glibc, the patch uses weak references unless
> > > gcc is compiled against glibc 2.26+.  strfromf128 unfortunately can't
> >
> > This support for older glibc doesn't actually seem to be working, on an
> > older system with glibc 2.19 I'm seeing
> >
> > /scratch/jmyers/fsf/gcc-mainline/libstdc++-v3/src/c++17/floating_to_chars.cc:52:3: error: expected initializer before '__asm'
> >    52 |   __asm ("strfromf128");
> >       |   ^~~~~
> >
> > and a series of subsequent errors.
> 
> This seems to "fix" it (not sure if it's right though):
> 
> #ifndef _GLIBCXX_HAVE_FLOAT128_MATH
> extern "C" _Float128 __strtof128(const char*, char**)
>  __attribute__((__weak__));
> #endif
> extern "C" _Float128 __strtof128(const char*, char**)
>  __asm ("strtof128");

It is, but floating_from_chars.cc has the same problem,
and I think we can avoid the duplication, like this:

2022-11-07  Jakub Jelinek  <jakub@redhat.com>

	* src/c++17/floating_from_chars.cc (__strtof128): Put __asm before
	__attribute__.
	* src/c++17/floating_to_chars.cc (__strfromf128): Likewise.

--- libstdc++-v3/src/c++17/floating_from_chars.cc.jj	2022-11-07 15:15:42.928314819 +0100
+++ libstdc++-v3/src/c++17/floating_from_chars.cc	2022-11-07 20:09:47.267983154 +0100
@@ -63,10 +63,11 @@ extern "C" __ieee128 __strtoieee128(cons
       && defined(__GLIBC_PREREQ)
 #define USE_STRTOF128_FOR_FROM_CHARS 1
 extern "C" _Float128 __strtof128(const char*, char**)
+  __asm ("strtof128")
 #ifndef _GLIBCXX_HAVE_FLOAT128_MATH
   __attribute__((__weak__))
 #endif
-  __asm ("strtof128");
+  ;
 #endif
 
 #if _GLIBCXX_FLOAT_IS_IEEE_BINARY32 && _GLIBCXX_DOUBLE_IS_IEEE_BINARY64 \
--- libstdc++-v3/src/c++17/floating_to_chars.cc.jj	2022-11-07 15:15:42.929314805 +0100
+++ libstdc++-v3/src/c++17/floating_to_chars.cc	2022-11-07 20:10:13.189627684 +0100
@@ -46,10 +46,11 @@ extern "C" int __sprintfieee128(char*, c
 #elif __FLT128_MANT_DIG__ == 113 && __LDBL_MANT_DIG__ != 113 \
       && defined(__GLIBC_PREREQ)
 extern "C" int __strfromf128(char*, size_t, const char*, _Float128)
+  __asm ("strfromf128")
 #ifndef _GLIBCXX_HAVE_FLOAT128_MATH
   __attribute__((__weak__))
 #endif
-  __asm ("strfromf128");
+  ;
 #endif
 
 // This implementation crucially assumes float/double have the


	Jakub