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[PATCH 15/16] Avoid stack-protecting certain functions called from assembly.

From: Nick Alcock <>

This is the problematic part.  Without -fno-stack-protector on
__pthread_mutex_cond_lock_adjust() and __pthread_mutex_unlock_usercnt(),
nptl/tst-cond24 and nptl/tst-cond25 receive a NULL mutex at unlock time
and segfault.  However... I don't understand why.  It is the callee's
responsibility both to add the stack canary and to initialize it, just
like any other local variable.  It has to be, or the ABI for stack-
protected code would be incompatible with that for non-protected code.
But the fact remains that
sysdeps/unix/sysv/linux/i386/pthread_cond_timedwait.S both explicitly
mentions the stack frame layout and calls this function, and this call
goes wrong if we stack-protect it.

So this is somewhere where I need someone to tell me what's special about
sysdeps/unix/sysv/linux/i386/pthread_cond_timedwait.S (and in particular
special about priority-inheritance mutexes: everything else works),
before I can be confident that this is even remotely the right thing to

We also de-stack-protect setjmp/sigjmp.c: it receives a sibcall from
sysdeps/x86_64/setjmp.S and lands in rtld, but is *not* rebuilt by
the machinery that rebuilds almost everything else that lands in
rtld with an appropriate MODULE_NAME.

Similar fixups may be required for things called directly from
assembly on other architectures.

v2: de-stack-protect setjmp/sigjmp.c.
v3: Use $(no-stack-protector).
v4: Use inhibit_stack_protector.
 nptl/pthread_mutex_lock.c   | 2 +-
 nptl/pthread_mutex_unlock.c | 2 +-
 setjmp/Makefile             | 4 ++++
 3 files changed, 6 insertions(+), 2 deletions(-)

diff --git a/nptl/pthread_mutex_lock.c b/nptl/pthread_mutex_lock.c
index bdfa529..87a1935 100644
--- a/nptl/pthread_mutex_lock.c
+++ b/nptl/pthread_mutex_lock.c
@@ -520,7 +520,7 @@ hidden_def (__pthread_mutex_lock)
 #ifdef NO_INCR
+internal_function inhibit_stack_protector
 __pthread_mutex_cond_lock_adjust (pthread_mutex_t *mutex)
   assert ((mutex->__data.__kind & PTHREAD_MUTEX_PRIO_INHERIT_NP) != 0);
diff --git a/nptl/pthread_mutex_unlock.c b/nptl/pthread_mutex_unlock.c
index 334ce38..5f23af1 100644
--- a/nptl/pthread_mutex_unlock.c
+++ b/nptl/pthread_mutex_unlock.c
@@ -33,7 +33,7 @@ __pthread_mutex_unlock_full (pthread_mutex_t *mutex, int decr)
-internal_function attribute_hidden
+internal_function inhibit_stack_protector attribute_hidden
 __pthread_mutex_unlock_usercnt (pthread_mutex_t *mutex, int decr)
   int type = PTHREAD_MUTEX_TYPE_ELISION (mutex);
diff --git a/setjmp/Makefile b/setjmp/Makefile
index 5b677cc..b617a84 100644
--- a/setjmp/Makefile
+++ b/setjmp/Makefile
@@ -35,3 +35,7 @@ tests-static	:= tst-setjmp-static
 include ../Rules
 $(objpfx)tst-setjmp-fp: $(libm)
+# This is sibcalled directly from arch-specific assembly, included in rtld,
+# but never rebuilt, so it must never be built with stack protection.
+CFLAGS-sigjmp.c += $(no-stack-protector)

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