Re: libposix build logs

[Bruno Haible]

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  <address@hidden>

        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 <address@hidden>.

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
 address@hidden@ @NEXT_FCNTL_H@