On 2023-09-01 09:56, Robin Murphy wrote:
> On 2023-08-31 12:59, Chunhui He wrote:
>>
>> On Tue, 29 Aug 2023 16:28:05 +0100, Robin Murphy
>> <[email protected]> wrote:
>>> On 29/08/2023 4:12 pm, Christoph Hellwig wrote:
>>>> On Tue, Aug 29, 2023 at 03:22:22PM +0100, Robin Murphy wrote:
>>>>> AFAICS, what that clearly says is that *C++* label attributes can be
>>>>> ambiguous. This is not C++ code. Even in C11, declarations still
>>>>> cannot be
>>>>> labelled, so it should still be the case that, per the same GCC
>>>>> documentation, "the ambiguity does not arise". And even if the
>>>>> language did
>>>>> allow it, an inline declaration at that point at the end of a function
>>>>> would be downright weird and against the kernel coding style anyway.
>>>>>
>>>>> So, I don't really see what's "better" about cluttering up C code with
>>>>> unnecessary C++isms; it's just weird noise to me. The only thing I
>>>>> think it
>>>>> *does* achieve is introduce the chance that the static checker brigade
>>>>> eventually identifies a redundant semicolon and we get more patches to
>>>>> remove it again.
>>
>> Inline declaration is a GNU C extension, so the ambiguity may arise.
>> Adding ';' makes the compiler easier to parse correctly, so I say
>> "better". The commit 13a453c241b78934a945b1af572d0533612c9bd1
>> (sched/fair: Add ';' after label attributes) also says the same.
>
> And that commit was also wrong. Nobody suggested C11 doesn't support
> inline declarations - it demonstrably does - the fact in question is
> that *attributes* on declarations is a C++ thing and not valid in C:
Argh, sorry, s/attributes/labels/
/me goes to make more coffee...
Robin.
> ~/src/linux$ git diff
> diff --git a/kernel/dma/pool.c b/kernel/dma/pool.c
> index 1acec2e22827..e1354235cb9c 100644
> --- a/kernel/dma/pool.c
> +++ b/kernel/dma/pool.c
> @@ -137,7 +137,8 @@ static int atomic_pool_expand(struct gen_pool *pool,
> size_t pool_size,
> dma_common_free_remap(addr, pool_size);
> #endif
> free_page: __maybe_unused
> - __free_pages(page, order);
> + int x = order;
> + __free_pages(page, x);
> out:
> return ret;
> }
> ~/src/linux$ make -j32
> CALL scripts/checksyscalls.sh
> CC kernel/dma/pool.o
> kernel/dma/pool.c: In function ‘atomic_pool_expand’:
> kernel/dma/pool.c:140:2: error: a label can only be part of a statement
> and a declaration is not a statement
> 140 | int x = order;
> | ^~~
> make[4]: *** [scripts/Makefile.build:243: kernel/dma/pool.o] Error 1
> make[3]: *** [scripts/Makefile.build:480: kernel/dma] Error 2
> make[2]: *** [scripts/Makefile.build:480: kernel] Error 2
> make[2]: *** Waiting for unfinished jobs....
> make[1]: *** [/home/robmur01/src/linux/Makefile:2032: .] Error 2
> make: *** [Makefile:234: __sub-make] Error 2
>
>
> Thanks,
> Robin.
>