Add error reporting (via errno) to getauxval().

[BZ 15846] As discussed in the recent thread on my $EXEC_ORIGIN patch
and in BZ 15846, getauxval() presently has no unambiguous way of
reporting an error condition.  It currently returns zero on error, but
this may also be a valid result for some auxv entries.  As there is no
clear invalid result for all current and future auxv entries, this patch
sets errno (following a suggestion in the BZ entry).

This version of the patch also adds documentation and tests for the
value-not-found conditions in getauxval().

2 files changed, 5 insertions, 2 deletions

diff --git a/misc/getauxval.c b/misc/getauxval.c
index e0317fd6f9..dd4c8ecab3 100644
--- a/misc/getauxval.c
+++ b/misc/getauxval.c
@@ -16,6 +16,7 @@
    <http://www.gnu.org/licenses/>.  */
 
 #include <sys/auxv.h>
+#include <errno.h>
 #include <ldsodefs.h>
 
 
@@ -32,6 +33,8 @@ __getauxval (unsigned long int type)
   for (p = GLRO(dl_auxv); p->a_type != AT_NULL; p++)
     if (p->a_type == type)
       return p->a_un.a_val;
+
+  __set_errno (ENOENT);
   return 0;
 }
 
diff --git a/misc/sys/auxv.h b/misc/sys/auxv.h
index a69250bd52..7aec3a04b8 100644
--- a/misc/sys/auxv.h
+++ b/misc/sys/auxv.h
@@ -27,9 +27,9 @@ __BEGIN_DECLS
 
 /* Return the value associated with an Elf*_auxv_t type from the auxv list
    passed to the program on startup.  If TYPE was not present in the auxv
-   list, returns zero.  */
+   list, returns zero and sets errno to ENOENT.  */
 extern unsigned long int getauxval (unsigned long int __type)
-  __THROW __attribute_const__;
+  __THROW;
 
 __END_DECLS