Description Andrey A. Chernov 2012-06-05 17:40:12 UTC

According to the current POSIX standard, errno must be saved across the
free() call, it is also recommendation of the future standard version
(Resolved state): http://austingroupbugs.net/view.php?id=385#c713

"However, earlier versions of this standard did not require this, and the
same example had to be written as:

    // buf was obtained by malloc(buflen)
    ret = write(fd, buf, buflen);
    if (ret < 0) {
        int save = errno;
        free(buf);
        errno = save;
        return ret;
    }
"
"earlier" here is current version. Please read whole problem description
and discussion at this URL too.

When I attempt to commit that recommended "save errno across free()"
way in realpath.c I got enough feedback showing that many members tend
to avoid mass code change needed for current standard strict compliance
and prefer to track unpublished standard instead, where free() must
not modify errno.

-current and -stable free() versions may issue some syscalls which
may modify errno (depends on debug flags, KTR, etc),
so I suggest to directly save and restore errno in the free()
to avoid any possible modifications.

Fix: 

+       serrno = errno;
+
	UTRACE(ptr, 0, 0);
	if (ptr != NULL) {
		assert(malloc_initialized);

		idalloc(ptr);
	}
+       errno = serrno;
 }

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Index: malloc.c
===================================================================
--- malloc.c    (revision 236135)
+++ malloc.c    (working copy)
@@ -6146,13 +6146,17 @@
 void
 free(void *ptr)
 {
+       int serrno;