path: root/arch
diff options
authorRich Felker <>2014-11-22 12:26:38 -0500
committerRich Felker <>2014-11-22 12:26:38 -0500
commit8cd0b11eafeaaec3df5113cb39094e5456ca6b22 (patch)
tree310e944d94172757e21a27734d4261ee1e6d8cea /arch
parent4a241f14a6bea81b9b50edda09f8184e35a75860 (diff)
fix __aeabi_read_tp oversight in arm atomics/tls overhaul
calls to __aeabi_read_tp may be generated by the compiler to access TLS on pre-v6 targets. previously, this function was hard-coded to call the kuser helper, which would crash on kernels with kuser helper removed. to fix the problem most efficiently, the definition of __aeabi_read_tp is moved so that it's an alias for the new __a_gettp. however, on v7+ targets, code to initialize the runtime choice of thread-pointer loading code is not even compiled, meaning that defining __aeabi_read_tp would have caused an immediate crash due to using the default implementation of __a_gettp with a HCF instruction. fortunately there is an elegant solution which reduces overall code size: putting the native thread-pointer loading instruction in the default code path for __a_gettp, so that separate default/native code paths are not needed. this function should never be called before __set_thread_area anyway, and if it is called early on pre-v6 hardware, the old behavior (crashing) is maintained. ideally __aeabi_read_tp would not be called at all on v7+ targets anyway -- in fact, prior to the overhaul, the same problem existed, but it was never caught by users building for v7+ with kuser disabled. however, it's possible for calls to __aeabi_read_tp to end up in a v7+ binary if some of the object files were built for pre-v7 targets, e.g. in the case of static libraries that were built separately, so this case needs to be handled.
Diffstat (limited to 'arch')
2 files changed, 5 insertions, 6 deletions
diff --git a/arch/arm/src/__set_thread_area.c b/arch/arm/src/__set_thread_area.c
index 680510ea..61d02827 100644
--- a/arch/arm/src/__set_thread_area.c
+++ b/arch/arm/src/__set_thread_area.c
@@ -9,7 +9,7 @@ extern const unsigned char __attribute__((__visibility__("hidden")))
__a_barrier_dummy[], __a_barrier_oldkuser[],
__a_barrier_v6[], __a_barrier_v7[],
__a_cas_dummy[], __a_cas_v6[], __a_cas_v7[],
- __a_gettp_dummy[], __a_gettp_native[];
+ __a_gettp_dummy[];
#define __a_barrier_kuser 0xffff0fa0
#define __a_cas_kuser 0xffff0fc0
@@ -26,7 +26,6 @@ int __set_thread_area(void *p)
#if !__ARM_ARCH_7A__ && !__ARM_ARCH_7R__ && __ARM_ARCH < 7
if (__hwcap & HWCAP_TLS) {
size_t *aux;
- SET(gettp, native);
SET(cas, v7);
SET(barrier, v7);
for (aux=libc.auxv; *aux; aux+=2) {
diff --git a/arch/arm/src/arm/atomics.s b/arch/arm/src/arm/atomics.s
index 9fcc7bd7..f241cc02 100644
--- a/arch/arm/src/arm/atomics.s
+++ b/arch/arm/src/arm/atomics.s
@@ -81,6 +81,10 @@ __a_cas_v7:
.word 0xf57ff05b /* dmb ish */
bx lr __aeabi_read_tp
+.type __aeabi_read_tp,%function
.global __a_gettp
.hidden __a_gettp
.type __a_gettp,%function
@@ -92,10 +96,6 @@ __a_gettp:
.global __a_gettp_dummy
.hidden __a_gettp_dummy
- .word 0xe7fddef1 __a_gettp_native
-.hidden __a_gettp_native
mrc p15,0,r0,c13,c0,3
bx lr