TLS (GNU/C11 thread-local storage) support for static-linked programs

the design for TLS in dynamic-linked programs is mostly complete too,
but I have not yet implemented it. cost is nonzero but still low for
programs which do not use TLS and/or do not use threads (a few hundred
bytes of new code, plus dependency on memcpy). i believe it can be
made smaller at some point by merging __init_tls and __init_security
into __libc_start_main and avoiding duplicate auxv-parsing code.

at the same time, I've also slightly changed the logic pthread_create
uses to allocate guard pages to ensure that guard pages are not
counted towards commit charge.

1 files changed, 15 insertions, 9 deletions

diff --git a/src/thread/pthread_self.c b/src/thread/pthread_self.c
index a8cc80b5..a93d8129 100644
--- a/src/thread/pthread_self.c
+++ b/src/thread/pthread_self.c
@@ -1,6 +1,6 @@
 #include "pthread_impl.h"
 
-static struct pthread main_thread;
+static struct pthread *main_thread = &(struct pthread){0};
 
 /* pthread_key_create.c overrides this */
 static const void *dummy[1] = { 0 };
@@ -10,14 +10,14 @@ static int init_main_thread()
 {
 	__syscall(SYS_rt_sigprocmask, SIG_UNBLOCK,
 		SIGPT_SET, 0, __SYSCALL_SSLEN);
-	if (__set_thread_area(&main_thread) < 0) return -1;
-	main_thread.canceldisable = libc.canceldisable;
-	main_thread.tsd = (void **)__pthread_tsd_main;
-	main_thread.errno_ptr = __errno_location();
-	main_thread.self = &main_thread;
-	main_thread.tid = main_thread.pid =
-		__syscall(SYS_set_tid_address, &main_thread.tid);
-	libc.main_thread = &main_thread;
+	if (__set_thread_area(main_thread) < 0) return -1;
+	main_thread->canceldisable = libc.canceldisable;
+	main_thread->tsd = (void **)__pthread_tsd_main;
+	main_thread->errno_ptr = __errno_location();
+	main_thread->self = main_thread;
+	main_thread->tid = main_thread->pid =
+		__syscall(SYS_set_tid_address, &main_thread->tid);
+	libc.main_thread = main_thread;
 	return 0;
 }
 
@@ -35,3 +35,9 @@ pthread_t __pthread_self_def()
 
 weak_alias(__pthread_self_def, pthread_self);
 weak_alias(__pthread_self_def, __pthread_self_init);
+
+void *__install_initial_tls(void *p)
+{
+	main_thread = p;
+	return __pthread_self_def();
+}