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From: Mark Rutland <mark.rutland@arm.com>
To: Miguel Ojeda <miguel.ojeda.sandonis@gmail.com>
Cc: linux-arm-kernel@lists.infradead.org, catalin.marinas@arm.com,
	lenb@kernel.org, linux-acpi@vger.kernel.org,
	linux-kernel@vger.kernel.org, mhiramat@kernel.org,
	ndesaulniers@google.com, ojeda@kernel.org, peterz@infradead.org,
	rafael.j.wysocki@intel.com, revest@chromium.org,
	robert.moore@intel.com, rostedt@goodmis.org, will@kernel.org
Subject: Re: [PATCH 1/8] Compiler attributes: GCC function alignment workarounds
Date: Thu, 12 Jan 2023 11:38:17 +0000	[thread overview]
Message-ID: <Y7/xKbOZYztcqz2b@FVFF77S0Q05N> (raw)
In-Reply-To: <Y77/qVgvaJidFpYt@FVFF77S0Q05N>

On Wed, Jan 11, 2023 at 06:27:53PM +0000, Mark Rutland wrote:
> On Mon, Jan 09, 2023 at 03:43:16PM +0100, Miguel Ojeda wrote:
> > On Mon, Jan 9, 2023 at 2:58 PM Mark Rutland <mark.rutland@arm.com> wrote:
> > >
> > > As far as I can tell, GCC doesn't respect '-falign-functions=N':
> > >
> > > * When the __weak__ attribute is used
> > >
> > >   GCC seems to forget the alignment specified by '-falign-functions=N',
> > >   but will respect the '__aligned__(N)' function attribute. Thus, we can
> > >   work around this by explciitly setting the alignment for weak
> > >   functions.
> > >
> > > * When the __cold__ attribute is used
> > >
> > >   GCC seems to forget the alignment specified by '-falign-functions=N',
> > >   and also doesn't seem to respect the '__aligned__(N)' function
> > >   attribute. The only way to work around this is to not use the __cold__
> > >   attibute.
> > 
> > If you happen to have a reduced case, then it would be nice to link it
> > in the commit. A bug report to GCC would also be nice.
> > 
> > I gave it a very quick try in Compiler Explorer, but I couldn't
> > reproduce it, so I guess it depends on flags, non-trivial functions or
> > something else.
> 
> So having spent today coming up with tests, it turns out it's not quite as I
> described above, but in a sense worse. I'm posting a summary here for
> posterity; I'll try to get this to compiler folk shortly.

I've added the cold bits to an existing ticket:

  https://gcc.gnu.org/bugzilla/show_bug.cgi?id=88345

I have not been able to reproduce the issue with __weak__, so I'll go dig into
that some more; it's likely I was mistaken there.

Thanks,
Mark.

WARNING: multiple messages have this Message-ID (diff)
From: Mark Rutland <mark.rutland@arm.com>
To: Miguel Ojeda <miguel.ojeda.sandonis@gmail.com>
Cc: linux-arm-kernel@lists.infradead.org, catalin.marinas@arm.com,
	lenb@kernel.org, linux-acpi@vger.kernel.org,
	linux-kernel@vger.kernel.org, mhiramat@kernel.org,
	ndesaulniers@google.com, ojeda@kernel.org, peterz@infradead.org,
	rafael.j.wysocki@intel.com, revest@chromium.org,
	robert.moore@intel.com, rostedt@goodmis.org, will@kernel.org
Subject: Re: [PATCH 1/8] Compiler attributes: GCC function alignment workarounds
Date: Thu, 12 Jan 2023 11:38:17 +0000	[thread overview]
Message-ID: <Y7/xKbOZYztcqz2b@FVFF77S0Q05N> (raw)
In-Reply-To: <Y77/qVgvaJidFpYt@FVFF77S0Q05N>

On Wed, Jan 11, 2023 at 06:27:53PM +0000, Mark Rutland wrote:
> On Mon, Jan 09, 2023 at 03:43:16PM +0100, Miguel Ojeda wrote:
> > On Mon, Jan 9, 2023 at 2:58 PM Mark Rutland <mark.rutland@arm.com> wrote:
> > >
> > > As far as I can tell, GCC doesn't respect '-falign-functions=N':
> > >
> > > * When the __weak__ attribute is used
> > >
> > >   GCC seems to forget the alignment specified by '-falign-functions=N',
> > >   but will respect the '__aligned__(N)' function attribute. Thus, we can
> > >   work around this by explciitly setting the alignment for weak
> > >   functions.
> > >
> > > * When the __cold__ attribute is used
> > >
> > >   GCC seems to forget the alignment specified by '-falign-functions=N',
> > >   and also doesn't seem to respect the '__aligned__(N)' function
> > >   attribute. The only way to work around this is to not use the __cold__
> > >   attibute.
> > 
> > If you happen to have a reduced case, then it would be nice to link it
> > in the commit. A bug report to GCC would also be nice.
> > 
> > I gave it a very quick try in Compiler Explorer, but I couldn't
> > reproduce it, so I guess it depends on flags, non-trivial functions or
> > something else.
> 
> So having spent today coming up with tests, it turns out it's not quite as I
> described above, but in a sense worse. I'm posting a summary here for
> posterity; I'll try to get this to compiler folk shortly.

I've added the cold bits to an existing ticket:

  https://gcc.gnu.org/bugzilla/show_bug.cgi?id=88345

I have not been able to reproduce the issue with __weak__, so I'll go dig into
that some more; it's likely I was mistaken there.

Thanks,
Mark.

_______________________________________________
linux-arm-kernel mailing list
linux-arm-kernel@lists.infradead.org
http://lists.infradead.org/mailman/listinfo/linux-arm-kernel

  reply	other threads:[~2023-01-12 11:49 UTC|newest]

Thread overview: 56+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2023-01-09 13:58 [PATCH 0/8] arm64/ftrace: Add support for DYNAMIC_FTRACE_WITH_CALL_OPS Mark Rutland
2023-01-09 13:58 ` Mark Rutland
2023-01-09 13:58 ` [PATCH 1/8] Compiler attributes: GCC function alignment workarounds Mark Rutland
2023-01-09 13:58   ` Mark Rutland
2023-01-09 14:43   ` Miguel Ojeda
2023-01-09 14:43     ` Miguel Ojeda
2023-01-09 17:06     ` Mark Rutland
2023-01-09 17:06       ` Mark Rutland
2023-01-09 22:35       ` Miguel Ojeda
2023-01-09 22:35         ` Miguel Ojeda
2023-01-11 18:27     ` Mark Rutland
2023-01-11 18:27       ` Mark Rutland
2023-01-12 11:38       ` Mark Rutland [this message]
2023-01-12 11:38         ` Mark Rutland
2023-01-13 12:49         ` Mark Rutland
2023-01-13 12:49           ` Mark Rutland
2023-01-15 21:32           ` Miguel Ojeda
2023-01-15 21:32             ` Miguel Ojeda
2023-01-09 13:58 ` [PATCH 2/8] ACPI: Don't build ACPICA with '-Os' Mark Rutland
2023-01-09 13:58   ` Mark Rutland
2023-01-09 18:30   ` kernel test robot
2023-01-10 15:40     ` Mark Rutland
2023-01-10 13:45   ` Rafael J. Wysocki
2023-01-10 13:45     ` Rafael J. Wysocki
2023-01-09 13:58 ` [PATCH 3/8] arm64: Extend support for CONFIG_FUNCTION_ALIGNMENT Mark Rutland
2023-01-09 13:58   ` Mark Rutland
2023-01-10 20:35   ` Peter Zijlstra
2023-01-10 20:35     ` Peter Zijlstra
2023-01-10 20:43     ` Will Deacon
2023-01-10 20:43       ` Will Deacon
2023-01-11 11:39       ` Mark Rutland
2023-01-11 11:39         ` Mark Rutland
2023-01-11 11:36     ` Mark Rutland
2023-01-11 11:36       ` Mark Rutland
2023-01-09 13:58 ` [PATCH 4/8] ftrace: Add DYNAMIC_FTRACE_WITH_CALL_OPS Mark Rutland
2023-01-09 13:58   ` Mark Rutland
2023-01-09 17:39   ` kernel test robot
2023-01-09 19:10   ` kernel test robot
2023-01-12  6:48   ` Li Huafei
2023-01-12  6:48     ` Li Huafei
2023-01-12 11:00     ` Mark Rutland
2023-01-12 11:00       ` Mark Rutland
2023-01-13  1:15       ` Li Huafei
2023-01-13  1:15         ` Li Huafei
2023-01-09 13:58 ` [PATCH 5/8] arm64: insn: Add helpers for BTI Mark Rutland
2023-01-09 13:58   ` Mark Rutland
2023-01-09 13:58 ` [PATCH 6/8] arm64: patching: Add aarch64_insn_write_literal_u64() Mark Rutland
2023-01-09 13:58   ` Mark Rutland
2023-01-09 13:58 ` [PATCH 7/8] arm64: ftrace: Update stale comment Mark Rutland
2023-01-09 13:58   ` Mark Rutland
2023-01-09 13:58 ` [PATCH 8/8] arm64: Implement HAVE_DYNAMIC_FTRACE_WITH_CALL_OPS Mark Rutland
2023-01-09 13:58   ` Mark Rutland
2023-01-10  8:55 ` [PATCH 0/8] arm64/ftrace: Add support for DYNAMIC_FTRACE_WITH_CALL_OPS David Laight
2023-01-10  8:55   ` David Laight
2023-01-10 10:31   ` Mark Rutland
2023-01-10 10:31     ` Mark Rutland

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