Make sure asprintf() is declared if it's present.

GNU libc is a pain.  If you don't define _GNU_SOURCE, it doesn't declare
asprintf().  If you *do* define _GNU_SOURCE, the strerror_r() it
declares isn't POSIX-compliant.

We use asprintf() if present, so we need it to be declared; define
_GNU_SOURCE in ftmacros.h.

At configuration time, if we have strerror_r(), check whether it's
GNU-style or POSIX-style, and define different #defines for those two
cases.  Handle GNU-style strerror_r() and POSIX-style strerror_r()
differently in pcap_fmt_errmsg_for_errno().

Make sure everything that uses asprintf() includes ftmacros.h before
including stdio.h.

1 files changed, 6 insertions, 12 deletions

diff --git a/ftmacros.h b/ftmacros.h
index de8da98e..cd3daebd 100644
--- a/ftmacros.h
+++ b/ftmacros.h
@@ -85,20 +85,14 @@
    */
 #elif defined(__linux__) || defined(linux) || defined(__linux)
   /*
-   * We can't turn _GNU_SOURCE on because some versions of GNU Libc
-   * will give the GNU version of strerror_r(), which returns a
-   * string pointer and doesn't necessarily fill in the buffer,
-   * rather than the standard version of strerror_r(), which
-   * returns 0 or an errno and always fills in the buffer.  We
-   * require both of the latter behaviors.
+   * Turn on _GNU_SOURCE to get everything GNU libc has to offer,
+   * including asprintf().
    *
-   * So we try turning everything else on that we can.  This includes
-   * defining _XOPEN_SOURCE as 600, because we want to force crypt()
-   * to be declared on systems that use GNU libc, such as most Linux
-   * distributions.
+   * Unfortunately, one thing it has to offer is a strerror_r()
+   * that's not POSIX-compliant, but we deal with that in
+   * pcap_fmt_errmsg_for_errno().
    */
-  #define _POSIX_C_SOURCE 200809L
-  #define _XOPEN_SOURCE 600
+  #define _GNU_SOURCE
 
   /*
    * We turn on both _DEFAULT_SOURCE and _BSD_SOURCE to try to get