* Re: [PATCH] include: drop pointless __compiler_offsetof indirection
2022-02-02 10:21 [PATCH] include: drop pointless __compiler_offsetof indirection Rasmus Villemoes
@ 2022-02-02 11:03 ` Miguel Ojeda
2022-02-02 16:01 ` Nathan Chancellor
` (2 subsequent siblings)
3 siblings, 0 replies; 5+ messages in thread
From: Miguel Ojeda @ 2022-02-02 11:03 UTC (permalink / raw)
To: Rasmus Villemoes
Cc: Nick Desaulniers, Miguel Ojeda, Andrew Morton, Nathan Chancellor,
Kees Cook, linux-kernel, llvm
On Wed, Feb 2, 2022 at 11:21 AM Rasmus Villemoes
<linux@rasmusvillemoes.dk> wrote:
>
> (1) compiler_types.h is unconditionally included via an -include
> flag (see scripts/Makefile.lib), and it defines __compiler_offsetof
> unconditionally. So testing for definedness of __compiler_offsetof is
> mostly pointless.
Sounds good to me.
By the way, there are a bunch of `#include <linux/compiler_types.h>`
around that could be removed.
> (2) Every relevant compiler provides __builtin_offsetof (even sparse
Indeed, even GCC 4.
Reviewed-by: Miguel Ojeda <ojeda@kernel.org>
Cheers,
Miguel
^ permalink raw reply [flat|nested] 5+ messages in thread* Re: [PATCH] include: drop pointless __compiler_offsetof indirection
2022-02-02 10:21 [PATCH] include: drop pointless __compiler_offsetof indirection Rasmus Villemoes
2022-02-02 11:03 ` Miguel Ojeda
@ 2022-02-02 16:01 ` Nathan Chancellor
2022-02-02 20:53 ` Kees Cook
2022-02-02 21:04 ` Nick Desaulniers
3 siblings, 0 replies; 5+ messages in thread
From: Nathan Chancellor @ 2022-02-02 16:01 UTC (permalink / raw)
To: Rasmus Villemoes
Cc: Nick Desaulniers, Miguel Ojeda, Andrew Morton, Kees Cook,
linux-kernel, llvm
On Wed, Feb 02, 2022 at 11:21:47AM +0100, Rasmus Villemoes wrote:
> (1) compiler_types.h is unconditionally included via an -include
> flag (see scripts/Makefile.lib), and it defines __compiler_offsetof
> unconditionally. So testing for definedness of __compiler_offsetof is
> mostly pointless.
>
> (2) Every relevant compiler provides __builtin_offsetof (even sparse
> has had that for 14 years), and if for whatever reason one would end
> up picking up the poor man's fallback definition (C file compiler with
> completely custom CFLAGS?), newer clang versions won't treat the
> result as an Integer Constant Expression, so if used in place where
> such is required (static initializer or static_assert), one would
> get errors like
>
> t.c:11:16: error: static_assert expression is not an integral constant expression
> t.c:11:16: note: cast that performs the conversions of a reinterpret_cast is not allowed in a constant expression
> t.c:4:33: note: expanded from macro 'offsetof'
> #define offsetof(TYPE, MEMBER) ((size_t)&((TYPE *)0)->MEMBER)
>
> So just define offsetof unconditionally and directly in terms of
> __builtin_offsetof.
>
> Signed-off-by: Rasmus Villemoes <linux@rasmusvillemoes.dk>
Reviewed-by: Nathan Chancellor <nathan@kernel.org>
> ---
> include/linux/compiler_types.h | 2 --
> include/linux/stddef.h | 6 +-----
> 2 files changed, 1 insertion(+), 7 deletions(-)
>
> diff --git a/include/linux/compiler_types.h b/include/linux/compiler_types.h
> index 3c1795fdb568..83ee7f7ada5d 100644
> --- a/include/linux/compiler_types.h
> +++ b/include/linux/compiler_types.h
> @@ -137,8 +137,6 @@ struct ftrace_likely_data {
> */
> #define __naked __attribute__((__naked__)) notrace
>
> -#define __compiler_offsetof(a, b) __builtin_offsetof(a, b)
> -
> /*
> * Prefer gnu_inline, so that extern inline functions do not emit an
> * externally visible function. This makes extern inline behave as per gnu89
> diff --git a/include/linux/stddef.h b/include/linux/stddef.h
> index ca507bd5f808..929d67710cc5 100644
> --- a/include/linux/stddef.h
> +++ b/include/linux/stddef.h
> @@ -13,11 +13,7 @@ enum {
> };
>
> #undef offsetof
> -#ifdef __compiler_offsetof
> -#define offsetof(TYPE, MEMBER) __compiler_offsetof(TYPE, MEMBER)
> -#else
> -#define offsetof(TYPE, MEMBER) ((size_t)&((TYPE *)0)->MEMBER)
> -#endif
> +#define offsetof(TYPE, MEMBER) __builtin_offsetof(TYPE, MEMBER)
>
> /**
> * sizeof_field() - Report the size of a struct field in bytes
> --
> 2.31.1
>
^ permalink raw reply [flat|nested] 5+ messages in thread* Re: [PATCH] include: drop pointless __compiler_offsetof indirection
2022-02-02 10:21 [PATCH] include: drop pointless __compiler_offsetof indirection Rasmus Villemoes
2022-02-02 11:03 ` Miguel Ojeda
2022-02-02 16:01 ` Nathan Chancellor
@ 2022-02-02 20:53 ` Kees Cook
2022-02-02 21:04 ` Nick Desaulniers
3 siblings, 0 replies; 5+ messages in thread
From: Kees Cook @ 2022-02-02 20:53 UTC (permalink / raw)
To: Rasmus Villemoes
Cc: Nick Desaulniers, Miguel Ojeda, Andrew Morton, Nathan Chancellor,
linux-kernel, llvm
On Wed, Feb 02, 2022 at 11:21:47AM +0100, Rasmus Villemoes wrote:
> (1) compiler_types.h is unconditionally included via an -include
> flag (see scripts/Makefile.lib), and it defines __compiler_offsetof
> unconditionally. So testing for definedness of __compiler_offsetof is
> mostly pointless.
>
> (2) Every relevant compiler provides __builtin_offsetof (even sparse
> has had that for 14 years), and if for whatever reason one would end
> up picking up the poor man's fallback definition (C file compiler with
> completely custom CFLAGS?), newer clang versions won't treat the
> result as an Integer Constant Expression, so if used in place where
> such is required (static initializer or static_assert), one would
> get errors like
>
> t.c:11:16: error: static_assert expression is not an integral constant expression
> t.c:11:16: note: cast that performs the conversions of a reinterpret_cast is not allowed in a constant expression
> t.c:4:33: note: expanded from macro 'offsetof'
> #define offsetof(TYPE, MEMBER) ((size_t)&((TYPE *)0)->MEMBER)
>
> So just define offsetof unconditionally and directly in terms of
> __builtin_offsetof.
>
> Signed-off-by: Rasmus Villemoes <linux@rasmusvillemoes.dk>
Yes please. :)
Reviewed-by: Kees Cook <keescook@chromium.org>
--
Kees Cook
^ permalink raw reply [flat|nested] 5+ messages in thread
* Re: [PATCH] include: drop pointless __compiler_offsetof indirection
2022-02-02 10:21 [PATCH] include: drop pointless __compiler_offsetof indirection Rasmus Villemoes
` (2 preceding siblings ...)
2022-02-02 20:53 ` Kees Cook
@ 2022-02-02 21:04 ` Nick Desaulniers
3 siblings, 0 replies; 5+ messages in thread
From: Nick Desaulniers @ 2022-02-02 21:04 UTC (permalink / raw)
To: Rasmus Villemoes
Cc: Miguel Ojeda, Andrew Morton, Nathan Chancellor, Kees Cook,
linux-kernel, llvm
On Wed, Feb 2, 2022 at 2:21 AM Rasmus Villemoes
<linux@rasmusvillemoes.dk> wrote:
>
> (1) compiler_types.h is unconditionally included via an -include
> flag (see scripts/Makefile.lib), and it defines __compiler_offsetof
> unconditionally. So testing for definedness of __compiler_offsetof is
> mostly pointless.
>
> (2) Every relevant compiler provides __builtin_offsetof (even sparse
> has had that for 14 years), and if for whatever reason one would end
> up picking up the poor man's fallback definition (C file compiler with
> completely custom CFLAGS?), newer clang versions won't treat the
> result as an Integer Constant Expression, so if used in place where
> such is required (static initializer or static_assert), one would
> get errors like
>
> t.c:11:16: error: static_assert expression is not an integral constant expression
> t.c:11:16: note: cast that performs the conversions of a reinterpret_cast is not allowed in a constant expression
> t.c:4:33: note: expanded from macro 'offsetof'
> #define offsetof(TYPE, MEMBER) ((size_t)&((TYPE *)0)->MEMBER)
>
> So just define offsetof unconditionally and directly in terms of
> __builtin_offsetof.
>
> Signed-off-by: Rasmus Villemoes <linux@rasmusvillemoes.dk>
> ---
> include/linux/compiler_types.h | 2 --
> include/linux/stddef.h | 6 +-----
> 2 files changed, 1 insertion(+), 7 deletions(-)
>
> diff --git a/include/linux/compiler_types.h b/include/linux/compiler_types.h
> index 3c1795fdb568..83ee7f7ada5d 100644
> --- a/include/linux/compiler_types.h
> +++ b/include/linux/compiler_types.h
> @@ -137,8 +137,6 @@ struct ftrace_likely_data {
> */
> #define __naked __attribute__((__naked__)) notrace
>
> -#define __compiler_offsetof(a, b) __builtin_offsetof(a, b)
> -
> /*
> * Prefer gnu_inline, so that extern inline functions do not emit an
> * externally visible function. This makes extern inline behave as per gnu89
> diff --git a/include/linux/stddef.h b/include/linux/stddef.h
> index ca507bd5f808..929d67710cc5 100644
> --- a/include/linux/stddef.h
> +++ b/include/linux/stddef.h
> @@ -13,11 +13,7 @@ enum {
> };
>
> #undef offsetof
> -#ifdef __compiler_offsetof
> -#define offsetof(TYPE, MEMBER) __compiler_offsetof(TYPE, MEMBER)
> -#else
> -#define offsetof(TYPE, MEMBER) ((size_t)&((TYPE *)0)->MEMBER)
RIP `((size_t)&((TYPE *)0)->MEMBER)`; you were beautiful in a way only
a mother could love.
Acked-by: Nick Desaulniers <ndesaulniers@google.com>
> -#endif
> +#define offsetof(TYPE, MEMBER) __builtin_offsetof(TYPE, MEMBER)
>
> /**
> * sizeof_field() - Report the size of a struct field in bytes
> --
> 2.31.1
>
--
Thanks,
~Nick Desaulniers
^ permalink raw reply [flat|nested] 5+ messages in thread