yann@1: Suggested by Jake Page <jake at cs dot stanford dot edu>
yann@1: in http://sources.redhat.com/ml/crossgcc/2004-07/msg00169.html
yann@1: but the libc-symbols.h fragment has been reworked to fix typos
yann@1: and to still work on gcc-2.95.3, which lacks _Pragma.
yann@1: 
yann@1: His comment was:
yann@1:  Fixes gcc-3.4 optimizing out comparisons to weak external symbols in code
yann@1:  like:
yann@1:   if (__pthread_mutex_init != NULL)
yann@1:     __pthread_mutex_init(...);
yann@1:  that causes segfaults during libc init when not linked to libpthread
yann@1: 
yann@1: diff -uNr glibc-2.2.5-orig/resolv/res_libc.c glibc-2.2.5/resolv/res_libc.c
yann@1: --- glibc-2.2.5-orig/resolv/res_libc.c	2001-02-12 12:23:34.000000000 -0800
yann@1: +++ glibc-2.2.5/resolv/res_libc.c	2004-07-27 22:56:32.000000000 -0700
yann@1: @@ -84,7 +84,8 @@
yann@1:  
yann@1:  #if SHLIB_COMPAT(libc, GLIBC_2_0, GLIBC_2_2)
yann@1:  # undef res_init
yann@1: -strong_alias (__res_init, __res_init_weak);
yann@1: +extern int __res_init_weak (void);
yann@1:  weak_extern (__res_init_weak);
yann@1: +strong_alias (__res_init, __res_init_weak);
yann@1:  compat_symbol (libc, __res_init_weak, res_init, GLIBC_2_0);
yann@1:  #endif
yann@1: --- glibc-2.2.5/include/libc-symbols.h.old	Fri Aug 13 04:20:55 2004
yann@1: +++ glibc-2.2.5/include/libc-symbols.h	Fri Aug 13 04:37:06 2004
yann@1: @@ -108,10 +108,16 @@
yann@1:  
yann@1:  /* Declare SYMBOL as weak undefined symbol (resolved to 0 if not defined).  */
yann@1:  #  define weak_extern(symbol) _weak_extern (symbol)
yann@1: -#  ifdef HAVE_ASM_WEAKEXT_DIRECTIVE
yann@1: -#   define _weak_extern(symbol) asm (".weakext " __SYMBOL_PREFIX #symbol);
yann@1: -#  else
yann@1: -#   define _weak_extern(symbol)    asm (".weak " __SYMBOL_PREFIX #symbol);
yann@1: +#  if __GNUC__ >= 3
yann@1: +    /* see http://sources.redhat.com/ml/libc-alpha/2003-01/msg00043.html */
yann@1: +#   define __weak_extern_1(expr) _Pragma(#expr)
yann@1: +#   define _weak_extern(symbol) __weak_extern_1(weak symbol)
yann@1: +#  else /* __GNUC__ == 2 */
yann@1: +#   ifdef HAVE_ASM_WEAKEXT_DIRECTIVE
yann@1: +#    define _weak_extern(symbol) asm (".weakext " __SYMBOL_PREFIX #symbol);
yann@1: +#   else
yann@1: +#    define _weak_extern(symbol)    asm (".weak " __SYMBOL_PREFIX #symbol);
yann@1: +#   endif
yann@1:  #  endif
yann@1:  
yann@1:  # else