[2.25 COMMITTED] Fix getting tunable values on big-endian (BZ #21109)

[Florian Weimer]

The code to set value passed a tunable_val_t, which when cast to
int32_t on big-endian gives the wrong value.  Instead, use
tunable_val_t.numval instead, which can then be safely cast into
int32_t.

(cherry picked from commit 8cbc826c37c0221ada65a7a622fe079b4e89a4b0)

2017-02-08  Siddhesh Poyarekar  <siddhesh@sourceware.org>

	[BZ #21109]
	* elf/dl-tunable-types.h (tunable_callback_t): Accept
	tunable_val_t as argument.
	* elf/dl-tunables.c (__tunable_set_val): Add comment.
	* malloc/arena.c (set_mallopt_check): Take tunable_val_t as
	argument.
	(DL_TUNABLE_CALLBACK_FNDECL): Likewise.

diff --git a/NEWS b/NEWS
index ec15dde..325cac7 100644
--- a/NEWS
+++ b/NEWS
@@ -5,6 +5,12 @@ See the end for copying conditions.
 Please send GNU C library bug reports via <http://sourceware.org/bugzilla/>
 using `glibc' in the "product" field.
 
+Version 2.25.1
+
+The following bugs are resolved with this release:
+
+  [21109] Tunables broken on big-endian
+
 Version 2.25
 
 * The feature test macro __STDC_WANT_LIB_EXT2__, from ISO/IEC TR
diff --git a/elf/dl-tunable-types.h b/elf/dl-tunable-types.h
index a986f0b..37a4e80 100644
--- a/elf/dl-tunable-types.h
+++ b/elf/dl-tunable-types.h
@@ -21,8 +21,6 @@
 # define _TUNABLE_TYPES_H_
 #include <stddef.h>
 
-typedef void (*tunable_callback_t) (void *);
-
 typedef enum
 {
   TUNABLE_TYPE_INT_32,
@@ -43,6 +41,8 @@ typedef union
   const char *strval;
 } tunable_val_t;
 
+typedef void (*tunable_callback_t) (tunable_val_t *);
+
 /* Security level for tunables.  This decides what to do with individual
    tunables for AT_SECURE binaries.  */
 typedef enum
diff --git a/elf/dl-tunables.c b/elf/dl-tunables.c
index a8d53d6..e42aa67 100644
--- a/elf/dl-tunables.c
+++ b/elf/dl-tunables.c
@@ -455,6 +455,8 @@ __tunable_set_val (tunable_id_t id, void *valp, tunable_callback_t callback)
   if (cur->strval == NULL)
     return;
 
+  /* Caller does not need the value, just call the callback with our tunable
+     value.  */
   if (valp == NULL)
     goto cb;
 
diff --git a/malloc/arena.c b/malloc/arena.c
index b91d7d6..d49e4a2 100644
--- a/malloc/arena.c
+++ b/malloc/arena.c
@@ -212,9 +212,9 @@ __malloc_fork_unlock_child (void)
 #if HAVE_TUNABLES
 static inline int do_set_mallopt_check (int32_t value);
 void
-DL_TUNABLE_CALLBACK (set_mallopt_check) (void *valp)
+DL_TUNABLE_CALLBACK (set_mallopt_check) (tunable_val_t *valp)
 {
-  int32_t value = *(int32_t *) valp;
+  int32_t value = (int32_t) valp->numval;
   do_set_mallopt_check (value);
   if (check_action != 0)
     __malloc_check_init ();
@@ -223,9 +223,9 @@ DL_TUNABLE_CALLBACK (set_mallopt_check) (void *valp)
 # define DL_TUNABLE_CALLBACK_FNDECL(__name, __type) \
 static inline int do_ ## __name (__type value);				      \
 void									      \
-DL_TUNABLE_CALLBACK (__name) (void *valp)				      \
+DL_TUNABLE_CALLBACK (__name) (tunable_val_t *valp)			      \
 {									      \
-  __type value = *(__type *) valp;					      \
+  __type value = (__type) (valp)->numval;				      \
   do_ ## __name (value);						      \
 }