diff mbox series

[40/46] x86/livepatch, lto: Disable live patching with gcc LTO

Message ID 20221114114344.18650-41-jirislaby@kernel.org
State New
Headers
Series gcc-LTO support for the kernel |

Commit Message

Jiri Slaby Nov. 14, 2022, 11:43 a.m. UTC 
  From: Andi Kleen <andi@firstfloor.org>

It is not supported by gcc 12 so far, so it causes compiler "sorry"
messages.

Other than the compiler support, there shouldn't be any barriers for
live patching LTOed kernels, although it might be more difficult to
create patches for larger functions.

Cc: Josh Poimboeuf <jpoimboe@kernel.org>
Cc: Jiri Kosina <jikos@kernel.org>
Cc: Miroslav Benes <mbenes@suse.cz>
Cc: Petr Mladek <pmladek@suse.com>
Cc: Joe Lawrence <joe.lawrence@redhat.com>
Cc: live-patching@vger.kernel.org
Signed-off-by: Andi Kleen <ak@linux.intel.com>
Signed-off-by: Martin Liska <mliska@suse.cz>
Signed-off-by: Jiri Slaby <jslaby@suse.cz>
---
 kernel/livepatch/Kconfig | 1 +
 1 file changed, 1 insertion(+)

Comments

Josh Poimboeuf Nov. 14, 2022, 7:07 p.m. UTC | #1 
On Mon, Nov 14, 2022 at 12:43:38PM +0100, Jiri Slaby (SUSE) wrote:
> From: Andi Kleen <andi@firstfloor.org>
> 
> It is not supported by gcc 12 so far, so it causes compiler "sorry"
> messages.

What specifically is not supported by GCC 12?  What are the "sorry"
messages?

> Other than the compiler support, there shouldn't be any barriers for
> live patching LTOed kernels, although it might be more difficult to
> create patches for larger functions.

This seems to conflict with the documentation.

> Cc: Josh Poimboeuf <jpoimboe@kernel.org>
> Cc: Jiri Kosina <jikos@kernel.org>
> Cc: Miroslav Benes <mbenes@suse.cz>
> Cc: Petr Mladek <pmladek@suse.com>
> Cc: Joe Lawrence <joe.lawrence@redhat.com>
> Cc: live-patching@vger.kernel.org
> Signed-off-by: Andi Kleen <ak@linux.intel.com>
> Signed-off-by: Martin Liska <mliska@suse.cz>
> Signed-off-by: Jiri Slaby <jslaby@suse.cz>
> ---
>  kernel/livepatch/Kconfig | 1 +
>  1 file changed, 1 insertion(+)
> 
> diff --git a/kernel/livepatch/Kconfig b/kernel/livepatch/Kconfig
> index 53d51ed619a3..22699adc39a6 100644
> --- a/kernel/livepatch/Kconfig
> +++ b/kernel/livepatch/Kconfig
> @@ -12,6 +12,7 @@ config LIVEPATCH
>  	depends on KALLSYMS_ALL
>  	depends on HAVE_LIVEPATCH
>  	depends on !TRIM_UNUSED_KSYMS
> +	depends on !LTO_GCC # not supported in gcc

The comment doesn't help.
Andi Kleen Nov. 14, 2022, 8:28 p.m. UTC | #2 
On Mon, Nov 14, 2022 at 11:07:42AM -0800, Josh Poimboeuf wrote:
> On Mon, Nov 14, 2022 at 12:43:38PM +0100, Jiri Slaby (SUSE) wrote:
> > From: Andi Kleen <andi@firstfloor.org>
> > 
> > It is not supported by gcc 12 so far, so it causes compiler "sorry"
> > messages.
> 
> What specifically is not supported by GCC 12? 

-fwhole-program and the live patching options are mutually exclusive.
Okay I suppose it could be handled by disabling -fwhole-program, although 
that might limit some optimizations.

> What are the "sorry" messages?

It's an error message from the compiler telling you that something is
not implemented.


-Andi
Josh Poimboeuf Nov. 14, 2022, 10 p.m. UTC | #3 
On Mon, Nov 14, 2022 at 12:28:09PM -0800, Andi Kleen wrote:
> On Mon, Nov 14, 2022 at 11:07:42AM -0800, Josh Poimboeuf wrote:
> > On Mon, Nov 14, 2022 at 12:43:38PM +0100, Jiri Slaby (SUSE) wrote:
> > > From: Andi Kleen <andi@firstfloor.org>
> > > 
> > > It is not supported by gcc 12 so far, so it causes compiler "sorry"
> > > messages.
> > 
> > What specifically is not supported by GCC 12? 
> 
> -fwhole-program and the live patching options are mutually exclusive.

What live patching options are you referring to?
Martin Liška Nov. 15, 2022, 1:32 p.m. UTC | #4 
On 11/14/22 23:00, Josh Poimboeuf wrote:
> On Mon, Nov 14, 2022 at 12:28:09PM -0800, Andi Kleen wrote:
>> On Mon, Nov 14, 2022 at 11:07:42AM -0800, Josh Poimboeuf wrote:
>>> On Mon, Nov 14, 2022 at 12:43:38PM +0100, Jiri Slaby (SUSE) wrote:
>>>> From: Andi Kleen <andi@firstfloor.org>
>>>>
>>>> It is not supported by gcc 12 so far, so it causes compiler "sorry"
>>>> messages.
>>>
>>> What specifically is not supported by GCC 12? 
>>
>> -fwhole-program and the live patching options are mutually exclusive.
> 
> What live patching options are you referring to?
> 

As mentioned in the reply to the next email, we speak about:
https://gcc.gnu.org/onlinedocs/gcc/Optimize-Options.html#index-flive-patching
option:

gcc -flto -flive-patching=inline-clone a.c
cc1: sorry, unimplemented: live patching is not supported with LTO

Cheers,
Martin
Song Liu Nov. 17, 2022, 8 p.m. UTC | #5 
On Mon, Nov 14, 2022 at 3:48 AM Jiri Slaby (SUSE) <jirislaby@kernel.org> wrote:
>
> From: Andi Kleen <andi@firstfloor.org>
>
> It is not supported by gcc 12 so far, so it causes compiler "sorry"
> messages.
>
> Other than the compiler support, there shouldn't be any barriers for
> live patching LTOed kernels, although it might be more difficult to
> create patches for larger functions.

A loosely related question: does livepatch work with CLANG LTO?
AFAICT, kpatch-build doesn't support it. But the kernel side should
work just fine?

Thanks,
Song

[...]
diff mbox series

Patch

diff --git a/kernel/livepatch/Kconfig b/kernel/livepatch/Kconfig
index 53d51ed619a3..22699adc39a6 100644
--- a/kernel/livepatch/Kconfig
+++ b/kernel/livepatch/Kconfig
@@ -12,6 +12,7 @@  config LIVEPATCH
 	depends on KALLSYMS_ALL
 	depends on HAVE_LIVEPATCH
 	depends on !TRIM_UNUSED_KSYMS
+	depends on !LTO_GCC # not supported in gcc
 	help
 	  Say Y here if you want to support kernel live patching.
 	  This option has no runtime impact until a kernel "patch"