From: Nick Desaulniers <ndesaulniers@google.com>
To: Miguel Ojeda <miguel.ojeda.sandonis@gmail.com>
Cc: LKML <linux-kernel@vger.kernel.org>,
Martin Sebor <msebor@gcc.gnu.org>, Arnd Bergmann <arnd@arndb.de>,
Laura Abbott <labbott@redhat.com>,
Luc Van Oostenryck <luc.vanoostenryck@gmail.com>,
Andrey Konovalov <andreyknvl@google.com>,
Kees Cook <keescook@chromium.org>,
Sean Christopherson <sean.j.christopherson@intel.com>
Subject: Re: [PATCH 2/3] Compiler Attributes: add support for __copy (gcc >= 9)
Date: Fri, 8 Feb 2019 16:41:44 -0800 [thread overview]
Message-ID: <CAKwvOd=hhSY9msLQvwWRjuYuqR7VtW8+Pr9+y-10_khzbtQ8_g@mail.gmail.com> (raw)
In-Reply-To: <20190209000840.11018-3-miguel.ojeda.sandonis@gmail.com>
On Fri, Feb 8, 2019 at 4:09 PM Miguel Ojeda
<miguel.ojeda.sandonis@gmail.com> wrote:
>
> From the GCC manual:
>
> copy
> copy(function)
>
> The copy attribute applies the set of attributes with which function
> has been declared to the declaration of the function to which
> the attribute is applied. The attribute is designed for libraries
> that define aliases or function resolvers that are expected
> to specify the same set of attributes as their targets. The copy
> attribute can be used with functions, variables, or types. However,
> the kind of symbol to which the attribute is applied (either
> function or variable) must match the kind of symbol to which
> the argument refers. The copy attribute copies only syntactic and
> semantic attributes but not attributes that affect a symbol’s
> linkage or visibility such as alias, visibility, or weak.
> The deprecated attribute is also not copied.
>
> https://gcc.gnu.org/onlinedocs/gcc/Common-Function-Attributes.html
>
> The upcoming GCC 9 release extends the -Wmissing-attributes warnings
> (enabled by -Wall) to C and aliases: it warns when particular function
> attributes are missing in the aliases but not in their target, e.g.:
>
> void __cold f(void) {}
> void __alias("f") g(void);
>
> diagnoses:
>
> warning: 'g' specifies less restrictive attribute than
> its target 'f': 'cold' [-Wmissing-attributes]
>
> Using __copy(f) we can copy the __cold attribute from f to g:
>
> void __cold f(void) {}
> void __copy(f) __alias("f") g(void);
>
> This attribute is most useful to deal with situations where an alias
> is declared but we don't know the exact attributes the target has.
>
> For instance, in the kernel, the widely used module_init/exit macros
> define the init/cleanup_module aliases, but those cannot be marked
> always as __init/__exit since they some modules do not have their
> functions marked as such.
Drop "they" from this sentence if there's a respin, otherwise looks helpful.
Reviewed-by: Nick Desaulniers <ndesaulniers@google.com>
>
> Suggested-by: Martin Sebor <msebor@gcc.gnu.org>
> Signed-off-by: Miguel Ojeda <miguel.ojeda.sandonis@gmail.com>
> ---
> include/linux/compiler_attributes.h | 14 ++++++++++++++
> 1 file changed, 14 insertions(+)
>
> diff --git a/include/linux/compiler_attributes.h b/include/linux/compiler_attributes.h
> index 19f32b0c29af..6b318efd8a74 100644
> --- a/include/linux/compiler_attributes.h
> +++ b/include/linux/compiler_attributes.h
> @@ -34,6 +34,7 @@
> #ifndef __has_attribute
> # define __has_attribute(x) __GCC4_has_attribute_##x
> # define __GCC4_has_attribute___assume_aligned__ (__GNUC_MINOR__ >= 9)
> +# define __GCC4_has_attribute___copy__ 0
> # define __GCC4_has_attribute___designated_init__ 0
> # define __GCC4_has_attribute___externally_visible__ 1
> # define __GCC4_has_attribute___noclone__ 1
> @@ -100,6 +101,19 @@
> */
> #define __attribute_const__ __attribute__((__const__))
>
> +/*
> + * Optional: only supported since gcc >= 9
> + * Optional: not supported by clang
> + * Optional: not supported by icc
> + *
> + * gcc: https://gcc.gnu.org/onlinedocs/gcc/Common-Function-Attributes.html#index-copy-function-attribute
> + */
> +#if __has_attribute(__copy__)
> +# define __copy(symbol) __attribute__((__copy__(symbol)))
> +#else
> +# define __copy(symbol)
> +#endif
> +
> /*
> * Don't. Just don't. See commit 771c035372a0 ("deprecate the '__deprecated'
> * attribute warnings entirely and for good") for more information.
> --
> 2.17.1
>
--
Thanks,
~Nick Desaulniers
next prev parent reply other threads:[~2019-02-09 0:41 UTC|newest]
Thread overview: 15+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-02-09 0:08 [PATCH 0/3] Clean the new GCC 9 -Wmissing-attributes warnings Miguel Ojeda
2019-02-09 0:08 ` [PATCH 1/3] lib/crc32.c: mark crc32_le_base/__crc32c_le_base aliases as __pure Miguel Ojeda
2019-02-09 0:08 ` [PATCH 2/3] Compiler Attributes: add support for __copy (gcc >= 9) Miguel Ojeda
2019-02-09 0:41 ` Nick Desaulniers [this message]
2019-02-09 12:36 ` Miguel Ojeda
2019-02-09 0:08 ` [PATCH 3/3] include/linux/module.h: copy __init/__exit attrs to init/cleanup_module Miguel Ojeda
2019-02-11 15:01 ` Jessica Yu
2019-02-09 10:44 ` [PATCH 0/3] Clean the new GCC 9 -Wmissing-attributes warnings Ard Biesheuvel
2019-02-09 11:19 ` Miguel Ojeda
2019-02-09 11:25 ` Ard Biesheuvel
2019-02-09 12:31 ` Miguel Ojeda
2019-02-11 16:21 ` Martin Sebor
2019-02-11 18:20 ` Ard Biesheuvel
2019-02-09 20:32 ` Laura Abbott
2019-02-13 17:30 ` Miguel Ojeda
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