Re: proposed new module careadlinkat (renamed from breadlinkat)

[Eric Blake]

On 03/31/2011 11:57 PM, Paul Eggert wrote:
> Following up on Bruno's comments, here's a revised proposed
> patch to gnulib, which I've tested with coreutils and with Emacs.
> 
> +#ifndef _GL_ALLOCATOR_H
> +
> +#include <stddef.h>
> +
> +struct allocator
> +{
> +  /* Call MALLOC to allocate memory, like 'malloc'.  On failure MALLOC
> +     should return NULL, though not necessarily set errno.  When given
> +     a zero size it may return NULL even if successful.  */
> +  void *(*malloc) (size_t);

Problem.  This is causing failures on mingw:

../../../gnulib/lib/careadlinkat.c: In function 'careadlinkat':
../../../gnulib/lib/careadlinkat.c:143:39: error: 'const struct
allocator' has no member named 'malloc'
../../../gnulib/lib/careadlinkat.c:149:66: error: 'const struct
allocator' has no member named 'realloc'
../../../gnulib/lib/careadlinkat.c:152:39: error: 'const struct
allocator' has no member named 'realloc'
../../../gnulib/lib/careadlinkat.c:169:27: error: 'const struct
allocator' has no member named 'malloc'
make[4]: *** [careadlinkat.lo] Error 1

It stems from the fact that on mingw, malloc and realloc are not POSIX
compliant, so they have been redefined to rpl_malloc and rpl_realloc by
the replacement <stdlib.h> prior to the time that "allocator.h" is
included.  Then you undefine those macros, and subsequent code is trying
to access different struct names:

> +
> +#include <config.h>
> +
> +#include "careadlinkat.h"
> +
> +#include "allocator.h"
> +
> +#include <errno.h>
> +#include <limits.h>
> +#include <stdlib.h>
> +#include <string.h>
> +#include <unistd.h>
> +
> +/* Use the system functions, not the gnulib overrides, because this
> +   module does not depend on GNU or POSIX semantics.  */
> +#undef malloc
> +#undef realloc

I'm pushing this as the simplest patch, but you may want to instead
consider renaming the field members to not shadow functions that might
have been #defined into replacement names.

diff --git i/ChangeLog w/ChangeLog
index 922d211..2c887a6 100644
--- i/ChangeLog
+++ w/ChangeLog
@@ -1,3 +1,9 @@
+2011-04-08  Eric Blake  <address@hidden>
+
+       careadlink: fix compilation error on mingw
+       * lib/careadlinkat.c (standard_allocator): Avoid renaming fields
+       within struct allocator.
+
 2011-04-06  Eric Blake  <address@hidden>

        binary-io: relicense under LGPLv2+
diff --git i/lib/careadlinkat.c w/lib/careadlinkat.c
index 15ffe24..eb2e009 100644
--- i/lib/careadlinkat.c
+++ w/lib/careadlinkat.c
@@ -30,11 +30,6 @@
 #include <string.h>
 #include <unistd.h>

-/* Use the system functions, not the gnulib overrides, because this
-   module does not depend on GNU or POSIX semantics.  */
-#undef malloc
-#undef realloc
-
 /* Define this independently so that stdint.h is not a prerequisite.  */
 #ifndef SIZE_MAX
 # define SIZE_MAX ((size_t) -1)
@@ -57,10 +52,10 @@ careadlinkatcwd (int fd, char const *filename, char
*buffer,
 }
 #endif

-/* A standard allocator.  For now, only careadlinkat needs this, but
-   perhaps it should be moved to the allocator module.  */
-static struct allocator const standard_allocator =
-  { malloc, realloc, free, NULL };
+/* Forward declaration.  We want to #undef malloc before initializing
+   this struct, but cannot do so until after all code that uses named
+   fields from "allocator.h" has been compiled.  */
+static struct allocator const standard_allocator;

 /* Assuming the current directory is FD, get the symbolic link value
    of FILENAME as a null-terminated string and put it into a buffer.
@@ -173,3 +168,14 @@ careadlinkat (int fd, char const *filename,
   errno = ENOMEM;
   return NULL;
 }
+
+/* Use the system functions, not the gnulib overrides, because this
+   module does not depend on GNU or POSIX semantics.  See comments
+   above why this must occur here.  */
+#undef malloc
+#undef realloc
+
+/* A standard allocator.  For now, only careadlinkat needs this, but
+   perhaps it should be moved to the allocator module.  */
+static struct allocator const standard_allocator =
+  { malloc, realloc, free, NULL };


-- 
Eric Blake   address@hidden    +1-801-349-2682
Libvirt virtualization library http://libvirt.org

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