From: Jonathan Wakely <jwakely.gcc@gmail.com>
To: Sebastian Huber <sebastian.huber@embedded-brains.de>
Cc: GCC Development <gcc@gcc.gnu.org>
Subject: Re: Why is there no libatomic default implementation using gthr.h?
Date: Mon, 19 Dec 2022 12:41:52 +0000 [thread overview]
Message-ID: <CAH6eHdTqCFODJm9TEkitMx2H2KoE86VV4JdAnC2PRDgOZ+wXSA@mail.gmail.com> (raw)
In-Reply-To: <1e90020b-ee25-9841-4def-7d6be6d91cb5@embedded-brains.de>
On Mon, 19 Dec 2022 at 11:19, Sebastian Huber wrote:
>
> Hello,
>
> I would like to fix the -fprofile-update=atomic implementation so that
> it works on all targets. Currently, it works only on targets with 64-bit
> atomic operations in hardware (and some special cases). I tried to fix
> it like this:
>
> https://gcc.gnu.org/pipermail/gcc-patches/2022-December/608620.html
>
> The problem with this patch is that it falls back to use functions
> provided by libatomic. The libatomic is currently not supported on all
> targets, for example:
>
> https://gcc.gnu.org/bugzilla/show_bug.cgi?id=77466
>
> https://gcc.gnu.org/bugzilla/show_bug.cgi?id=77378
>
> Why is there no libatomic default implementation using gthr.h?
>
> The C++ library already depends on gthr.h and installs the headers in
> "bits/gthr.h" etc. For this the libstdc++-v3 configure/Makefile
> duplicates some logic from libgcc. Why is the gthr.h stuff not installed
> by libgcc itself?
Because libstdc++ installs a modified copy of the libgcc headers. Are
those modifications suitable for all users of the libgcc version of
the header?
>
> In libatomic, the POSIX implementation could be easily rewritten to use
> the gthr interface.
Why would that need gthr.h to be installed? The use of gthreads should
be an internal implementation detail, not exposed as part of the
libatomic API.
>
> Any objections to do the following?
>
> 1. Install gthr.h to "bits/gthr.h" by libgcc (including the other gthr
> headers).
>
> 2. Remove the gthr configure/Makefile support from libstdc++-v3.
I would be concerned by these two steps.
> 3. Use gthr as the default implementation of libatomic.
I have no objection to doing this, but I don't see why you need to
touch libstdc++ to do it. Just make libatomic create its own copy of
gthr.h (if a fallback gthreads-based implementation is actually
needed) and compile that locally in the libatomic build dir. That
shouldn't need changes to libgcc or libstdc++, should it?
next prev parent reply other threads:[~2022-12-19 12:42 UTC|newest]
Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-12-19 9:03 Sebastian Huber
2022-12-19 12:41 ` Jonathan Wakely [this message]
2022-12-19 12:45 ` Sebastian Huber
2022-12-19 12:56 ` LIU Hao
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