Disable __longjmp_chk protection

glibc implements some checking on longjmp() calls by replacing it with
an internal function __longjmp_chk(), when FORTIFY_SOURCE is defined.
This can be problematic when compiling the library under one version of
glibc and running it under another. Work around this issue for the one
symbol affected for now, before taking out the undef hammer.

Fixes http://code.google.com/p/webm/issues/detail?id=166

Change-Id: Ifc5e25cdec17915e394711f2185b3e9214572d10

vpx/internal/vpx_codec_internal.h

@@ -45,6 +45,7 @@
 #define VPX_CODEC_INTERNAL_H
 #include "../vpx_decoder.h"
 #include "../vpx_encoder.h"
+#include "vpx_config.h"
 #include <stdarg.h>
 
 
@@ -435,6 +436,23 @@ vpx_codec_pkt_list_get(struct vpx_codec_pkt_list *list,
 
 #include <stdio.h>
 #include <setjmp.h>
+
+/* GLIBC started intercepting calls to longjmp in version 2.11, if the
+ * FORTIFY_SOURCE flag is defined (it's defined by default on Ubuntu).
+ * This can cause problems running under older versions of GLIBC (ie,
+ * for binary distributions), so work around it by linking to the
+ * underlying longjmp call directly.
+ */
+#if defined(__GNUC_PREREQ)
+#if __GNUC_PREREQ (2,11)
+#if ARCH_X86_64
+__asm__(".symver __longjmp_chk,longjmp@GLIBC_2.2.5");
+#else
+__asm__(".symver __longjmp_chk,longjmp@GLIBC_2.0");
+#endif
+#endif
+#endif
+
 struct vpx_internal_error_info
 {
     vpx_codec_err_t  error_code;