From: Sebastian Huber <sebastian.huber@embedded-brains.de>
To: Richard Biener <richard.guenther@gmail.com>
Cc: gcc-patches@gcc.gnu.org
Subject: Re: [PATCH] gcov: Fix -fprofile-update=atomic
Date: Fri, 16 Dec 2022 11:39:54 +0100 [thread overview]
Message-ID: <a822810d-2b95-0ad1-5991-1f5246c66859@embedded-brains.de> (raw)
In-Reply-To: <CAFiYyc0-1mgZr8Ne078HuiLbdAo1E1nTgNngKRhNSeFvTZNMJA@mail.gmail.com>
On 16.12.22 10:47, Richard Biener wrote:
>> No, if you select -fprofile-update=atomic, then the updates shall be
>> atomic from my point of view. If a fallback is acceptable, then you can
>> use -fprofile-update=prefer-atomic. Using the fallback in
>> -fprofile-update=atomic is a bug which prevents the use of gcov for
>> multi-threaded applications on the lower end targets which do not have
>> atomic operations in hardware.
> Ah, OK. So the fallback there is libatomic calls as well then? Note
> not all targets support libatomic, for those the failure mode is likely
> a link error (which might be fine, but we eventually might want to
> amend documentation to indicate this failure mode).
It seems these library calls caused issues in the past:
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=77466
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=77378
One option could be to emit calls to a new libgcov function:
__gcov_inc_counter(counter) -> updated value
This function could use a __gthread_mutex_t mutex for updates. This ends
up probably with quite a bad performance.
--
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next prev parent reply other threads:[~2022-12-16 10:39 UTC|newest]
Thread overview: 7+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-12-09 13:56 Sebastian Huber
2022-12-13 14:30 ` Richard Biener
2022-12-15 8:34 ` Sebastian Huber
2022-12-16 9:47 ` Richard Biener
2022-12-16 10:39 ` Sebastian Huber [this message]
2022-12-16 12:09 ` Richard Biener
2022-12-16 13:01 ` Sebastian Huber
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