[PATCH 1/2] util/getauxval: Ensure setting errno if not found

[Vivian Wang]

Sometimes zero is a valid value for getauxval (e.g. AT_EXECFD). Make
sure that we can distinguish between a valid zero value and a not found
entry by setting errno.

Ignore getauxval from sys/auxv.h on glibc < 2.19 because it does not set
errno.

Signed-off-by: Vivian Wang <uwu@dram.page>
---
 util/getauxval.c | 14 ++++++++++++--
 1 file changed, 12 insertions(+), 2 deletions(-)

diff --git a/util/getauxval.c b/util/getauxval.c
index b124107d61..f1008bdc59 100644
--- a/util/getauxval.c
+++ b/util/getauxval.c
@@ -24,7 +24,13 @@
 
 #include "qemu/osdep.h"
 
-#ifdef CONFIG_GETAUXVAL
+/* If glibc < 2.19, getauxval can't be used because it does not set errno if
+   entry is not found. */
+#if defined(CONFIG_GETAUXVAL) && \
+    (!defined(__GLIBC__) \
+        || __GLIBC__ > 2 \
+        || (__GLIBC__ == 2 && __GLIBC_MINOR__ >= 19))
+
 /* Don't inline this in qemu/osdep.h, because pulling in <sys/auxv.h> for
    the system declaration of getauxval pulls in the system <elf.h>, which
    conflicts with qemu's version.  */
@@ -95,6 +101,7 @@ unsigned long qemu_getauxval(unsigned long type)
         }
     }
 
+    errno = ENOENT;
     return 0;
 }
 
@@ -104,7 +111,9 @@ unsigned long qemu_getauxval(unsigned long type)
 unsigned long qemu_getauxval(unsigned long type)
 {
     unsigned long aux = 0;
-    elf_aux_info(type, &aux, sizeof(aux));
+    int ret = elf_aux_info(type, &aux, sizeof(aux));
+    if (ret != 0)
+        errno = ret;
     return aux;
 }
 
@@ -112,6 +121,7 @@ unsigned long qemu_getauxval(unsigned long type)
 
 unsigned long qemu_getauxval(unsigned long type)
 {
+    errno = ENOSYS;
     return 0;
 }
 
-- 
2.45.1