From 29d6dbc906f51f127700fd9e2d1e1170456f2382 Mon Sep 17 00:00:00 2001 From: Ryan Prichard Date: Fri, 19 Oct 2018 20:35:23 -0700 Subject: [PATCH] Move Bionic slots to the end of pthread_internal_t With ELF TLS, the static linker assumes that an executable's TLS segment is at a known offset from the thread pointer (i.e. __get_tls()). The segment can be located prior to the TP (variant 2, x86[_64], sparc) or after it (variant 1, arm{32,64}, ppc, mips, ia64, riscv). We can't make our pthread_internal_t exactly follow the ordinary arm64 ABI (at least) because TP[5] is used for clang's -fstack-protector on Android. Instead, reserve extra space after the TP (up to 16 words), which will be followed by the executable's TLS segment. Bug: http://b/78026329 Test: boot device, bionic unit tests Change-Id: I0f3b270b793f9872ba0effeac03f4dec364438d6 Merged-In: I0f3b270b793f9872ba0effeac03f4dec364438d6 (cherry picked from commit f397317e96928ef24b980d5c73d08829c0e70cd4) --- libc/bionic/pthread_internal.h | 10 ++++++---- 1 file changed, 6 insertions(+), 4 deletions(-) diff --git a/libc/bionic/pthread_internal.h b/libc/bionic/pthread_internal.h index 65ec5ff2b..b68cb942f 100644 --- a/libc/bionic/pthread_internal.h +++ b/libc/bionic/pthread_internal.h @@ -112,10 +112,6 @@ class pthread_internal_t { thread_local_dtor* thread_local_dtors; - void* tls[BIONIC_TLS_SLOTS]; - - pthread_key_data_t key_data[BIONIC_PTHREAD_KEY_COUNT]; - /* * The dynamic linker implements dlerror(3), which makes it hard for us to implement this * per-thread buffer by simply using malloc(3) and free(3). @@ -124,6 +120,12 @@ class pthread_internal_t { char dlerror_buffer[__BIONIC_DLERROR_BUFFER_SIZE]; bionic_tls* bionic_tls; + + pthread_key_data_t key_data[BIONIC_PTHREAD_KEY_COUNT]; + + // The thread pointer (__get_tls()) points at this field. This field must come last so that + // an executable's TLS segment can be allocated at a fixed offset after the thread pointer. + void* tls[BIONIC_TLS_SLOTS]; }; __LIBC_HIDDEN__ int __init_thread(pthread_internal_t* thread);