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    SubjectRe: [PATCH v2 01/16] slab: Remove __malloc attribute from realloc functions
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    Kees Cook <keescook@chromium.org> writes:
    > On Wed, Sep 28, 2022 at 09:26:15AM +0200, Geert Uytterhoeven wrote:
    >> On Fri, Sep 23, 2022 at 10:35 PM Kees Cook <keescook@chromium.org> wrote:
    >> > The __malloc attribute should not be applied to "realloc" functions, as
    >> > the returned pointer may alias the storage of the prior pointer. Instead
    >> > of splitting __malloc from __alloc_size, which would be a huge amount of
    >> > churn, just create __realloc_size for the few cases where it is needed.
    >> >
    >> > Additionally removes the conditional test for __alloc_size__, which is
    >> > always defined now.
    >> >
    >> > Cc: Christoph Lameter <cl@linux.com>
    >> > Cc: Pekka Enberg <penberg@kernel.org>
    >> > Cc: David Rientjes <rientjes@google.com>
    >> > Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com>
    >> > Cc: Andrew Morton <akpm@linux-foundation.org>
    >> > Cc: Vlastimil Babka <vbabka@suse.cz>
    >> > Cc: Roman Gushchin <roman.gushchin@linux.dev>
    >> > Cc: Hyeonggon Yoo <42.hyeyoo@gmail.com>
    >> > Cc: Marco Elver <elver@google.com>
    >> > Cc: linux-mm@kvack.org
    >> > Signed-off-by: Kees Cook <keescook@chromium.org>
    >>
    >> Thanks for your patch, which is now commit 63caa04ec60583b1 ("slab:
    >> Remove __malloc attribute from realloc functions") in next-20220927.
    >>
    >> Noreply@ellerman.id.au reported all gcc8-based builds to fail
    >> (e.g. [1], more at [2]):
    >>
    >> In file included from <command-line>:
    >> ./include/linux/percpu.h: In function ‘__alloc_reserved_percpu’:
    >> ././include/linux/compiler_types.h:279:30: error: expected
    >> declaration specifiers before ‘__alloc_size__’
    >> #define __alloc_size(x, ...) __alloc_size__(x, ## __VA_ARGS__) __malloc
    >> ^~~~~~~~~~~~~~
    >> ./include/linux/percpu.h:120:74: note: in expansion of macro ‘__alloc_size’
    >> [...]
    >>
    >> It's building fine with e.g. gcc-9 (which is my usual m68k cross-compiler).
    >> Reverting this commit on next-20220927 fixes the issue.
    >>
    >> [1] http://kisskb.ellerman.id.au/kisskb/buildresult/14803908/
    >> [2] http://kisskb.ellerman.id.au/kisskb/head/1bd8b75fe6adeaa89d02968bdd811ffe708cf839/
    >
    > Eek! Thanks for letting me know. I'm confused about this --
    > __alloc_size__ wasn't optional in compiler_attributes.h -- but obviously
    > I broke something! I'll go figure this out.

    This fixes it for me.

    cheers

    diff --git a/include/linux/compiler_types.h b/include/linux/compiler_types.h
    index f141a6f6b9f6..0717534f8364 100644
    --- a/include/linux/compiler_types.h
    +++ b/include/linux/compiler_types.h
    @@ -275,8 +275,13 @@ struct ftrace_likely_data {
    * be performing a _reallocation_, as that may alias the existing pointer.
    * For these, use __realloc_size().
    */
    -#define __alloc_size(x, ...) __alloc_size__(x, ## __VA_ARGS__) __malloc
    -#define __realloc_size(x, ...) __alloc_size__(x, ## __VA_ARGS__)
    +#ifdef __alloc_size__
    +# define __alloc_size(x, ...) __alloc_size__(x, ## __VA_ARGS__) __malloc
    +# define __realloc_size(x, ...) __alloc_size__(x, ## __VA_ARGS__)
    +#else
    +# define __alloc_size(x, ...) __malloc
    +# define __realloc_size(x, ...)
    +#endif

    #ifndef asm_volatile_goto
    #define asm_volatile_goto(x...) asm goto(x)
    \
     
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