Gary V. Vaughan wrote:
>> ix86 RHEL 4 gcc 3.4.6 (test-fcntl-h-c++.cc compile failed:
>> 133: symbol `mknod' already defined)
>> x86_64 RHEL 4i gcc 3.4.6 (test-fcntl-h-c++.cc compile failed:
>> 124: symbol `mknod' already defined
>> 149: symbol `lstat' already defined
>> 172: symbol `fstat' already defined)
The problem is here is a combination of the glibc headers and the name
mangling in g++ versions < 4.3.
glibc's <sys/stat.h> defines mknod et al. as inline functions. Also,
glibc's <fcntl.h> include <sys/stat.h> inside an extern "C" block. This
is usually frowned upon, and here leads to the error. It leads to a compilation
unit that essentially looks like this:
=============================================================================================
extern "C" {
extern "C" {
extern int mknod (__const char *__path, unsigned int __mode, unsigned long int
__dev)
throw () __attribute__ ((__nonnull__ (1)));
extern int __xmknod (int __ver, __const char *__path, unsigned int __mode,
unsigned long int *__dev) throw () __attribute__ ((__nonnull__ (2, 4)));
extern __inline__ int
mknod (__const char *__path, unsigned int __mode, unsigned long int __dev)
throw ()
{
return __xmknod (0, __path, __mode, &__dev);
}
}
namespace gnulib { static int (*mknod) (char const *file, unsigned int mode,
unsigned long int dev) = ::mknod; } extern "C" int _gl_cxxalias_dummy;
extern __typeof__ (mknod) mknod;
}
int (*global_mknod) (__const char *__path, unsigned int __mode, unsigned long
int __dev) = gnulib::mknod;
=============================================================================================
When you compile this with a g++ version < 4.3 and no optimization, you will
see that in the .s file the label 'mknod' is defined twice:
$ g++ -S bug.cc && grep mknod bug.s
.long _GLOBAL__I_global_mknod
movl mknod, %eax
movl %eax, global_mknod
.type _GLOBAL__I_global_mknod, @function
_GLOBAL__I_global_mknod:
.size _GLOBAL__I_global_mknod, .-_GLOBAL__I_global_mknod
.section .text.mknod,"axG",@progbits,mknod,comdat
.weak mknod
.type mknod, @function
mknod:
call __xmknod
.size mknod, .-mknod
.globl global_mknod
.type global_mknod, @object
.size global_mknod, 4
global_mknod:
.type mknod, @object
.size mknod, 4
mknod:
.long mknod
The fix is to remove the extern "C" { ... } bracket around the
namespace gnulib { ... } portion of the code. When this is done,
the variable 'gnulib::mknod' gets the name mangling _ZN6gnulib5mknodE
instead of plain mknod.
2010-11-11 Bruno Haible <br...@clisp.org>
fcntl-h: Fix for use of C++ on glibc systems.
* lib/fcntl.in.h: Include <sys/stat.h> before include_next <fcntl.h>
also on glibc systems in C++ mode.
Reported by Gary V. Vaughan <g...@gnu.org>.
2--- lib/fcntl.in.h.orig Fri Nov 12 03:19:39 2010
+++ lib/fcntl.in.h Fri Nov 12 03:18:45 2010
@@ -26,7 +26,13 @@
/* Special invocation convention. */
#include <sys/types.h>
-#ifndef __GLIBC__ /* Avoid namespace pollution on glibc systems. */
+/* On some systems other than glibc, <sys/stat.h> is a prerequisite of
+ <fcntl.h>. On glibc systems, we would like to avoid namespace pollution.
+ But on glibc systems, <fcntl.h> includes <sys/stat.h> inside an
+ extern "C" { ... } block, which leads to errors in C++ mode with the
+ overridden <sys/stat.h> from gnulib. These errors are known to be gone
+ with g++ version >= 4.3. */
+#if !defined __GLIBC__ || (defined __cplusplus && defined GNULIB_NAMESPACE &&
!(__GNUC__ > 4 || (__GNUC__ == 4 && __GNUC_MINOR__ >= 3)))
# include <sys/stat.h>
#endif
#...@include_next@ @NEXT_FCNTL_H@
