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