Re: [PATCH 08/41] arm64: Replace __ASSEMBLY__ with __ASSEMBLER__ in uapi headers

[Thomas Huth <thuth@redhat.com>]

On 14/03/2025 14.42, Will Deacon wrote:
> On Fri, Mar 14, 2025 at 01:05:15PM +0100, Arnd Bergmann wrote:
>> On Fri, Mar 14, 2025, at 12:55, Will Deacon wrote:
>>> On Fri, Mar 14, 2025 at 08:09:39AM +0100, Thomas Huth wrote:
>>>> __ASSEMBLY__ is only defined by the Makefile of the kernel, so
>>>> this is not really useful for uapi headers (unless the userspace
>>>> Makefile defines it, too). Let's switch to __ASSEMBLER__ which
>>>> gets set automatically by the compiler when compiling assembly
>>>> code.
>>>>
>>>> Cc: Catalin Marinas <catalin.marinas@arm.com>
>>>> Cc: Will Deacon <will@kernel.org>
>>>> Signed-off-by: Thomas Huth <thuth@redhat.com>
>>>> ---
>>>>   arch/arm64/include/uapi/asm/kvm.h        | 2 +-
>>>>   arch/arm64/include/uapi/asm/ptrace.h     | 4 ++--
>>>>   arch/arm64/include/uapi/asm/sigcontext.h | 4 ++--
>>>>   3 files changed, 5 insertions(+), 5 deletions(-)
>>>
>>> Is there a risk of breaking userspace with this? I wonder if it would
>>> be more conservative to do something like:
>>>
>>> #if !defined(__ASSEMBLY__) && !defined(__ASSEMBLER__)
>>>
>>> so that if somebody is doing '#define __ASSEMBLY__' then they get the
>>> same behaviour as today.
>>>
>>> Or maybe we don't care?
>>
>> I think the main risk we would have is user applications relying
>> on the __ASSEMBLER__ checks in new kernel headers and not defining
>> __ASSEMBLY__. This would result in the application not building
>> against old kernel headers that only check against __ASSEMBLY__.
> 
> Hmm. I hadn't thought about the case of old headers :/
> 
> A quick Debian codesearch shows that glibc might #define __ASSEMBLY__
> for some arch-specific headers:
> 
> https://codesearch.debian.net/search?q=%23define+__ASSEMBLY__&literal=1
> 
> which is what I was more worried about.

  Hi!

FWIW, the x86 patches have been merged since kernel v6.15, and as far as I 
know, there haven't been any complaints about the change there yet. Thus I 
assume the changes should be ok.

So I rebased the arm64 patch now, too, and resend them separately as a v2:

  https://lore.kernel.org/lkml/20251010130116.828465-1-thuth@redhat.com/

  Thomas