Fix pthread_getattr_np for the main thread.
On most architectures the kernel subtracts a random offset to the stack
pointer in create_elf_tables by calling arch_align_stack before writing
the auxval table and so on. On all but x86 this doesn't cause a problem
because the random offset is less than a page, but on x86 it's up to two
pages. This means that our old technique of rounding the stack pointer
doesn't work. (Our old implementation of that technique was wrong too.)
It's also incorrect to assume that the main thread's stack base and size
are constant. Likewise to assume that the main thread has a guard page.
The main thread is not like other threads.
This patch switches to reading /proc/self/maps (and checking RLIMIT_STACK)
whenever we're asked.
Bug: 17111575
Signed-off-by: Fengwei Yin <fengwei.yin@intel.com>
Change-Id: I1d4dbffe7bc7bda1d353c3a295dbf68d29f63158
diff --git a/libc/bionic/libc_init_common.cpp b/libc/bionic/libc_init_common.cpp
index ff9940e..2a6a03b 100644
--- a/libc/bionic/libc_init_common.cpp
+++ b/libc/bionic/libc_init_common.cpp
@@ -36,7 +36,6 @@
#include <stdlib.h>
#include <sys/auxv.h>
#include <sys/time.h>
-#include <sys/resource.h>
#include <unistd.h>
#include "private/bionic_auxv.h"
@@ -46,7 +45,6 @@
#include "pthread_internal.h"
extern "C" abort_msg_t** __abort_message_ptr;
-extern "C" uintptr_t __get_sp(void);
extern "C" int __system_properties_init(void);
extern "C" int __set_tls(void* ptr);
extern "C" int __set_tid_address(int* tid_address);
@@ -62,17 +60,6 @@
// Declared in "private/bionic_ssp.h".
uintptr_t __stack_chk_guard = 0;
-static size_t get_main_thread_stack_size() {
- rlimit stack_limit;
- int rlimit_result = getrlimit(RLIMIT_STACK, &stack_limit);
- if ((rlimit_result == 0) &&
- (stack_limit.rlim_cur != RLIM_INFINITY) &&
- (stack_limit.rlim_cur > PTHREAD_STACK_MIN)) {
- return (stack_limit.rlim_cur & ~(PAGE_SIZE - 1));
- }
- return PTHREAD_STACK_SIZE_DEFAULT;
-}
-
/* Init TLS for the initial thread. Called by the linker _before_ libc is mapped
* in memory. Beware: all writes to libc globals from this function will
* apply to linker-private copies and will not be visible from libc later on.
@@ -96,16 +83,15 @@
main_thread.tid = __set_tid_address(&main_thread.tid);
main_thread.set_cached_pid(main_thread.tid);
- // Work out the extent of the main thread's stack.
- uintptr_t stack_top = (__get_sp() & ~(PAGE_SIZE - 1)) + PAGE_SIZE;
- size_t stack_size = get_main_thread_stack_size();
- void* stack_bottom = reinterpret_cast<void*>(stack_top - stack_size);
-
// We don't want to free the main thread's stack even when the main thread exits
// because things like environment variables with global scope live on it.
+ // We also can't free the pthread_internal_t itself, since that lives on the main
+ // thread's stack rather than on the heap.
pthread_attr_init(&main_thread.attr);
- pthread_attr_setstack(&main_thread.attr, stack_bottom, stack_size);
main_thread.attr.flags = PTHREAD_ATTR_FLAG_USER_ALLOCATED_STACK | PTHREAD_ATTR_FLAG_MAIN_THREAD;
+ main_thread.attr.guard_size = 0; // The main thread has no guard page.
+ main_thread.attr.stack_size = 0; // User code should never see this; we'll compute it when asked.
+ // TODO: the main thread's sched_policy and sched_priority need to be queried.
__init_thread(&main_thread, false);
__init_tls(&main_thread);