From ac31bf278d9ed855e6765bb71d64ed19d2b7c0f8 Mon Sep 17 00:00:00 2001
From: Rich Felker <dalias@aerifal.cx>
Date: Tue, 10 Jun 2014 04:49:49 -0400
Subject: [PATCH] simplify errno implementation

the motivation for the errno_ptr field in the thread structure, which
this commit removes, was to allow the main thread's errno to keep its
address when lazy thread pointer initialization was used. &errno was
evaluated prior to setting up the thread pointer and stored in
errno_ptr for the main thread; subsequently created threads would have
errno_ptr pointing to their own errno_val in the thread structure.

since lazy initialization was removed, there is no need for this extra
level of indirection; __errno_location can simply return the address
of the thread's errno_val directly. this does cause &errno to change,
but the change happens before entry to application code, and thus is
not observable.
---
 src/env/__init_tls.c         | 1 -
 src/errno/__errno_location.c | 2 +-
 src/internal/pthread_impl.h  | 2 +-
 src/thread/pthread_create.c  | 1 -
 4 files changed, 2 insertions(+), 4 deletions(-)

diff --git a/src/env/__init_tls.c b/src/env/__init_tls.c
index e1a2b614..f7eab8d6 100644
--- a/src/env/__init_tls.c
+++ b/src/env/__init_tls.c
@@ -16,7 +16,6 @@ int __init_tp(void *p)
 	if (!r) libc.can_do_threads = 1;
 	libc.has_thread_pointer = 1;
 	td->tid = td->pid = __syscall(SYS_set_tid_address, &td->tid);
-	td->errno_ptr = &td->errno_val;
 	return 0;
 }
 
diff --git a/src/errno/__errno_location.c b/src/errno/__errno_location.c
index 84191076..49654efd 100644
--- a/src/errno/__errno_location.c
+++ b/src/errno/__errno_location.c
@@ -3,6 +3,6 @@
 int *__errno_location(void)
 {
 	static int e;
-	if (libc.has_thread_pointer) return __pthread_self()->errno_ptr;
+	if (libc.has_thread_pointer) return &__pthread_self()->errno_val;
 	return &e;
 }
diff --git a/src/internal/pthread_impl.h b/src/internal/pthread_impl.h
index 2e910b3e..650e8115 100644
--- a/src/internal/pthread_impl.h
+++ b/src/internal/pthread_impl.h
@@ -18,7 +18,7 @@ struct pthread {
 	uintptr_t sysinfo;
 	uintptr_t canary;
 	pid_t tid, pid;
-	int tsd_used, errno_val, *errno_ptr;
+	int tsd_used, errno_val;
 	volatile int cancel, canceldisable, cancelasync;
 	int detached;
 	unsigned char *map_base;
diff --git a/src/thread/pthread_create.c b/src/thread/pthread_create.c
index 7a2f172c..e9c8160a 100644
--- a/src/thread/pthread_create.c
+++ b/src/thread/pthread_create.c
@@ -201,7 +201,6 @@ int pthread_create(pthread_t *restrict res, const pthread_attr_t *restrict attrp
 	new->stack = stack;
 	new->stack_size = stack - stack_limit;
 	new->pid = self->pid;
-	new->errno_ptr = &new->errno_val;
 	new->start = entry;
 	new->start_arg = arg;
 	new->self = new;
-- 
2.25.1