Cygwin 64 does not support shared library weak references as no
references may be undefined in Windows DLLs.
Recent gnulib versions (at least 29-31 in bison, wget, and wget2)
default Cygwin to gl_cv_have_weak=yes.
Bruno Haible has applied a patch (referenced below and in the attached)
to gnulib threadlib.m4 serial 31, and I have applied a modified version
to serial 29:
<https://lists.gnu.org/archive/html/bug-gnulib/2021-09/msg00063.html>.
* m4/threadlib.m4 (gl_WEAK_SYMBOLS): Force a "guessing no" result on Cygwin.
The actual patch is in:
https://lists.gnu.org/archive/html/bug-gnulib/2021-09/msg00068.html
--
Take care. Thanks, Brian Inglis, Calgary, Alberta, Canada
This email may be disturbing to some readers as it contains
too much technical detail. Reader discretion is advised.
[Data in binary units and prefixes, physical quantities in SI.]
2021-09-17 Bruno Haible <[email protected]>
threadlib: Avoid crashes in thread-related functions on Cygwin 3.2.0.
Reported by Brian Inglis via Akim Demaille in
<https://lists.gnu.org/archive/html/bug-gnulib/2021-09/msg00063.html>.
* m4/threadlib.m4 (gl_WEAK_SYMBOLS): Force a "guessing no" result on
Cygwin.
diff -w --git origsrc/m4/threadlib.m4 src/m4/threadlib.m4
index 37b797c18..6b43bbdfa 100644
--- origsrc/m4/threadlib.m4 2021-08-02 23:51:08.000000000 -0600
+++ src/m4/threadlib.m4 2021-09-17 15:17:37.103525500 -0600
@@ -1,4 +1,4 @@
-# threadlib.m4 serial 31
+# threadlib.m4 serial 32
dnl Copyright (C) 2005-2021 Free Software Foundation, Inc.
dnl This file is free software; the Free Software Foundation
dnl gives unlimited permission to copy and/or distribute it,
@@ -84,38 +84,48 @@ AC_DEFUN([gl_WEAK_SYMBOLS],
AC_REQUIRE([AC_CANONICAL_HOST])
AC_CACHE_CHECK([whether imported symbols can be declared weak],
[gl_cv_have_weak],
- [gl_cv_have_weak=no
- dnl First, test whether the compiler accepts it syntactically.
- AC_LINK_IFELSE(
- [AC_LANG_PROGRAM(
- [[extern void xyzzy ();
+ [case "$host_os" in
+ cygwin*)
+ dnl On Cygwin 3.2.0 with gcc 10.2, the test below would succeed, but
+ dnl programs that use pthread_in_use() with weak symbol references
+ dnl crash miserably at runtime.
+ gl_cv_have_weak="guessing no"
+ ;;
+ *)
+ gl_cv_have_weak=no
+ dnl First, test whether the compiler accepts it syntactically.
+ AC_LINK_IFELSE(
+ [AC_LANG_PROGRAM(
+ [[extern void xyzzy ();
#pragma weak xyzzy]],
- [[xyzzy();]])],
- [gl_cv_have_weak=maybe])
- if test $gl_cv_have_weak = maybe; then
- dnl Second, test whether it actually works. On Cygwin 1.7.2, with
- dnl gcc 4.3, symbols declared weak always evaluate to the address 0.
- AC_RUN_IFELSE(
- [AC_LANG_SOURCE([[
+ [[xyzzy();]])],
+ [gl_cv_have_weak=maybe])
+ if test $gl_cv_have_weak = maybe; then
+ dnl Second, test whether it actually works. On Cygwin 1.7.2, with
+ dnl gcc 4.3, symbols declared weak always evaluate to the address 0.
+ AC_RUN_IFELSE(
+ [AC_LANG_SOURCE([[
#include <stdio.h>
#pragma weak fputs
int main ()
{
return (fputs == NULL);
}]])],
- [gl_cv_have_weak=yes],
- [gl_cv_have_weak=no],
- [dnl When cross-compiling, assume that only ELF platforms support
- dnl weak symbols.
- AC_EGREP_CPP([Extensible Linking Format],
- [#ifdef __ELF__
- Extensible Linking Format
- #endif
- ],
- [gl_cv_have_weak="guessing yes"],
- [gl_cv_have_weak="guessing no"])
- ])
- fi
+ [gl_cv_have_weak=yes],
+ [gl_cv_have_weak=no],
+ [dnl When cross-compiling, assume that only ELF platforms support
+ dnl weak symbols.
+ AC_EGREP_CPP([Extensible Linking Format],
+ [#ifdef __ELF__
+ Extensible Linking Format
+ #endif
+ ],
+ [gl_cv_have_weak="guessing yes"],
+ [gl_cv_have_weak="guessing no"])
+ ])
+ fi
+ ;;
+ esac
dnl But when linking statically, weak symbols don't work.
case " $LDFLAGS " in
*" -static "*) gl_cv_have_weak=no ;;
