From: Tom de Vries <tdevries@suse.de>
To: gcc-patches@gcc.gnu.org
Subject: [PATCH][libatomic] Fix return value in libat_test_and_set
Date: Thu, 24 Mar 2022 09:28:15 +0100 [thread overview]
Message-ID: <20220324082813.GA6633@delia.home> (raw)
Hi,
On nvptx (using a Quadro K2000 with driver 470.103.01) I ran into this:
...
FAIL: gcc.dg/atomic/stdatomic-flag-2.c -O1 execution test
...
which mimimized to:
...
#include <stdatomic.h>
atomic_flag a = ATOMIC_FLAG_INIT;
int main () {
if ((atomic_flag_test_and_set) (&a))
__builtin_abort ();
return 0;
}
...
The atomic_flag_test_and_set is implemented using __atomic_test_and_set_1,
which corresponds to the "word-sized compare-and-swap loop" version of
libat_test_and_set in libatomic/tas_n.c.
The semantics of a test-and-set is that the return value is "true if and only
if the previous contents were 'set'".
But the code uses:
...
return woldval != 0;
...
which means it doesn't look only at the byte that was either set or not set,
but at the entire word.
Fix this by using instead:
...
return (woldval & wval) == wval;
...
Tested on nvptx.
OK for trunk?
Thanks,
- Tom
[libatomic] Fix return value in libat_test_and_set
---
libatomic/tas_n.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/libatomic/tas_n.c b/libatomic/tas_n.c
index d0d8c283b49..65eaa7753a5 100644
--- a/libatomic/tas_n.c
+++ b/libatomic/tas_n.c
@@ -73,7 +73,7 @@ SIZE(libat_test_and_set) (UTYPE *mptr, int smodel)
__ATOMIC_RELAXED, __ATOMIC_RELAXED));
post_barrier (smodel);
- return woldval != 0;
+ return (woldval & wval) == wval;
}
#define DONE 1
next reply other threads:[~2022-03-24 8:28 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-03-24 8:28 Tom de Vries [this message]
2022-03-24 9:02 ` Jakub Jelinek
2022-03-24 10:01 ` Tom de Vries
2022-03-24 10:59 ` Jakub Jelinek
2022-03-24 12:08 ` Tom de Vries
2022-03-24 12:25 ` Jakub Jelinek
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=20220324082813.GA6633@delia.home \
--to=tdevries@suse.de \
--cc=gcc-patches@gcc.gnu.org \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for read-only IMAP folder(s) and NNTP newsgroup(s).