[glibc] misc: Add internal __getauxval2 function

[Florian Weimer]

https://sourceware.org/git/gitweb.cgi?p=glibc.git;h=562ef5e69eb38230810bd25a4335224a31bfe31b

commit 562ef5e69eb38230810bd25a4335224a31bfe31b
Author: Florian Weimer <fweimer@redhat.com>
Date:   Tue Oct 27 10:42:10 2020 +0100

    misc: Add internal __getauxval2 function
    
    The explicit error return value (without in-band signaling) avoids
    complicated steps to detect errors based on whether errno has been
    updated.
    
    Reviewed-by: Alistair Francis <alistair.francis@wdc.com>

Diff:
---
 include/sys/auxv.h |  5 +++++
 misc/getauxval.c   | 33 +++++++++++++++++++++++++++------
 2 files changed, 32 insertions(+), 6 deletions(-)

diff --git a/include/sys/auxv.h b/include/sys/auxv.h
index 3bab6d05d4..dd0602b08d 100644
--- a/include/sys/auxv.h
+++ b/include/sys/auxv.h
@@ -5,4 +5,9 @@
 extern __typeof (getauxval) __getauxval;
 libc_hidden_proto (__getauxval)
 
+/* Like getauxval, but writes the value to *RESULT and returns true if
+   found, or returns false.  Does not set errno.  */
+_Bool __getauxval2 (unsigned long int type, unsigned long int *result);
+libc_hidden_proto (__getauxval2)
+
 #endif  /* !_ISOMAC */
diff --git a/misc/getauxval.c b/misc/getauxval.c
index d7f9f957d0..e96d4dfa20 100644
--- a/misc/getauxval.c
+++ b/misc/getauxval.c
@@ -18,26 +18,47 @@
 #include <sys/auxv.h>
 #include <errno.h>
 #include <ldsodefs.h>
+#include <stdbool.h>
 
-
-unsigned long int
-__getauxval (unsigned long int type)
+bool
+__getauxval2 (unsigned long int type, unsigned long int *result)
 {
 #ifdef HAVE_AUX_VECTOR
   ElfW(auxv_t) *p;
 #endif
 
   if (type == AT_HWCAP)
-    return GLRO(dl_hwcap);
+    {
+      *result = GLRO(dl_hwcap);
+      return true;
+    }
   else if (type == AT_HWCAP2)
-    return GLRO(dl_hwcap2);
+    {
+      *result = GLRO(dl_hwcap2);
+      return true;
+    }
 
 #ifdef HAVE_AUX_VECTOR
   for (p = GLRO(dl_auxv); p->a_type != AT_NULL; p++)
     if (p->a_type == type)
-      return p->a_un.a_val;
+      {
+        *result = p->a_un.a_val;
+        return true;
+      }
 #endif
 
+  return false;
+}
+libc_hidden_def (__getauxval2)
+
+unsigned long int
+__getauxval (unsigned long int type)
+{
+  unsigned long int result;
+
+  if (__getauxval2 (type, &result))
+    return result;
+
   __set_errno (ENOENT);
   return 0;
 }