Re: pthread_key_create bug?

[Markus Wichmann <nullplan@gmx.net>]

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On Sun, Jan 06, 2019 at 09:11:28PM -0500, Rich Felker wrote:
> See commit 84d061d5a31c9c773e29e1e2b1ffe8cb9557bc58.
> 
> Rich

Speaking of that commit: Am I missing something? The log message of that
commit says that pthread_key_delete was stuffed into another file to
avoid __synccall() being pulled into programs not referencing
pthread_key_delete(). Yet pthread_key_create.c contains
clean_dirty_tsd(), which contains a hard dependency on
__pthread_key_delete_synccall(), which will do the synccall, and thus
pull everything in.

I appreciate that the function in question can never be called unless
pthread_key_delete() is used, but the linker can't know that. The
compiler can't see code of the other compilation units and thus has to
generate code containing a reference to __pthread_key_delete_synccall(),
and the linker can't see that the reference is unreachable unless
__pthread_key_delete() is linked in...

Wait a minute. If we made that a weak reference, that would already
suffice. Wouldn't even necessarily need an alias, since it is
unreachable without pthread_key_delete() anyway.

Is the attached patch acceptable?

Ciao,
Markus

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From 851f8bb89d9fae664a0d6018fce251ab64d737b7 Mon Sep 17 00:00:00 2001
From: Markus Wichmann <nullplan@gmx.net>
Date: Mon, 7 Jan 2019 18:07:34 +0100
Subject: [PATCH 4/4] Add weak reference to reduce static size.

Commit 84d061d5a31c9c773e29e1e2b1ffe8cb9557bc58 claimed to try and
reduce the static size for programs referencing pthread_key_create() but
not pthread_key_delete(). Unfortunately, the critical reference was
still strong, so the __synccall() mechanism was pulled in, anyway. This
commit makes the reference weak, so it is resolved to NULL if
pthread_key_delete() is not used, but in that case the function is
unreachable, anyway.
---
 src/thread/pthread_key_create.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/src/thread/pthread_key_create.c b/src/thread/pthread_key_create.c
index e26f199c..31ed0826 100644
--- a/src/thread/pthread_key_create.c
+++ b/src/thread/pthread_key_create.c
@@ -35,6 +35,8 @@ static void clean_dirty_tsd_callback(void *p)
 	if (args->caller == self) args->ret = 0;
 }
 
+extern hidden weak void __pthread_key_delete_synccall(void (*f)(void *), void *p);
+
 static int clean_dirty_tsd(void)
 {
 	struct cleanup_args args = {
-- 
2.19.1