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().

1 files changed, 26 insertions, 2 deletions

diff --git a/elf/tst-auxv.c b/elf/tst-auxv.c
index 454c0b0..0fb3ad5 100644
--- a/elf/tst-auxv.c
+++ b/elf/tst-auxv.c
@@ -16,6 +16,7 @@
    <http://www.gnu.org/licenses/>.  */
 
 #include <elf.h>
+#include <errno.h>
 #include <link.h>
 #include <string.h>
 #include <stdio.h>
@@ -25,14 +26,37 @@
 static int
 do_test (int argc, char *argv[])
 {
-  const char *execfn = (const char *) getauxval (AT_EXECFN);
+  errno = 0;
+  const char *execfn = (const char *) getauxval (AT_NULL);
+
+  if (errno != ENOENT)
+    {
+      printf ("errno is %d rather than %d (ENOENT) on failure\n", errno,
+	      ENOENT);
+      return 1;
+    }
+
+  if (execfn != NULL)
+    {
+      printf ("getauxval return value is nonzero on failure\n");
+      return 1;
+    }
+
+  errno = 0;
+  execfn = (const char *) getauxval (AT_EXECFN);
 
   if (execfn == NULL)
     {
-      printf ("No AT_EXECFN found, test skipped\n");
+      printf ("No AT_EXECFN found, AT_EXECFN test skipped\n");
       return 0;
     }
 
+  if (errno != 0)
+    {
+      printf ("errno erroneously set to %d on success\n", errno);
+      return 1;
+    }
+
   if (strcmp (argv[0], execfn) != 0)
     {
       printf ("Mismatch: argv[0]: %s vs. AT_EXECFN: %s\n", argv[0], execfn);