Cache getpid.
In practice, with this implementation we never need to make a system call.
We get the main thread's tid (which is the same as our pid) back from
the set_tid_address system call we have to make during initialization.
A new pthread will have the same pid as its parent, and a fork child's
main (and only) thread will have a pid equal to its tid, which we get for
free from the kernel before clone returns.
The only time we'd actually have to make a getpid system call now is if
we take a signal during fork and the signal handler calls getpid. (That,
or we call getpid in the dynamic linker while it's still dealing with its
own relocations and hasn't even set up the main thread yet.)
Bug: 15387103
Change-Id: I6d4718ed0a5c912fc75b5f738c49a023dbed5189
diff --git a/libc/bionic/libc_init_common.cpp b/libc/bionic/libc_init_common.cpp
index abf2d36..fa61c3c 100644
--- a/libc/bionic/libc_init_common.cpp
+++ b/libc/bionic/libc_init_common.cpp
@@ -86,21 +86,24 @@
void __libc_init_tls(KernelArgumentBlock& args) {
__libc_auxv = args.auxv;
- uintptr_t stack_top = (__get_sp() & ~(PAGE_SIZE - 1)) + PAGE_SIZE;
- size_t stack_size = get_main_thread_stack_size();
- uintptr_t stack_bottom = stack_top - stack_size;
-
static void* tls[BIONIC_TLS_SLOTS];
static pthread_internal_t main_thread;
main_thread.tls = tls;
// Tell the kernel to clear our tid field when we exit, so we're like any other pthread.
+ // As a side-effect, this tells us our pid (which is the same as the main thread's tid).
main_thread.tid = __set_tid_address(&main_thread.tid);
+ main_thread.set_cached_pid(main_thread.tid);
- // We already have a stack, and we don't want to free it up on exit (because things like
- // environment variables with global scope live on it).
+ // 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.
pthread_attr_init(&main_thread.attr);
- pthread_attr_setstack(&main_thread.attr, (void*) stack_bottom, stack_size);
+ 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;
__init_thread(&main_thread, false);