Re: [RFC][PATCH] Update -Wattribute-alias for gcc9

From: Arnd Bergmann
Date: Fri Jan 25 2019 - 05:58:41 EST


On Fri, Jan 25, 2019 at 11:43 AM Laura Abbott <labbott@xxxxxxxxxx> wrote:
>
> Commit bee20031772a ("disable -Wattribute-alias warning for
> SYSCALL_DEFINEx()") disabled -Wattribute-alias with gcc8.
> gcc9 changed the format of -Wattribute-alias to take a parameter.
> This doesn't quite match with the existing disabling mechanism
> so update for gcc9 to match with the default (-Wattribute-alias=1).
>
> Signed-off-by: Laura Abbott <labbott@xxxxxxxxxx>
> ---
> This is RFC because it feels ugly. I went ahead and did the obvious fixup
> but it's worth discussing if we're going to end up with an explosion or
> if there's a better way to handle this in one macro.

Bernd Edlinger has sent a patch to gcc for this:
https://gcc.gnu.org/ml/gcc-patches/2019-01/msg01120.html

and Miguel Ojeda said he wanted to send a patch for it to the
kernel as well, not sure if he wanted to take a different
approach there, so adding both to Cc here.

Arnd




> ---
> include/linux/compat.h | 2 ++
> include/linux/compiler-gcc.h | 7 ++++++-
> include/linux/syscalls.h | 2 ++
> 3 files changed, 10 insertions(+), 1 deletion(-)
>
> diff --git a/include/linux/compat.h b/include/linux/compat.h
> index 056be0d03722..d5d7700f26a6 100644
> --- a/include/linux/compat.h
> +++ b/include/linux/compat.h
> @@ -75,6 +75,8 @@
> __diag_push(); \
> __diag_ignore(GCC, 8, "-Wattribute-alias", \
> "Type aliasing is used to sanitize syscall arguments");\
> + __diag_ignore(GCC, 9, "-Wattribute-alias=1", \
> + "Type aliasing is used to sanitize syscall arguments");\
> asmlinkage long compat_sys##name(__MAP(x,__SC_DECL,__VA_ARGS__)); \
> asmlinkage long compat_sys##name(__MAP(x,__SC_DECL,__VA_ARGS__)) \
> __attribute__((alias(__stringify(__se_compat_sys##name)))); \
> diff --git a/include/linux/compiler-gcc.h b/include/linux/compiler-gcc.h
> index e8579412ad21..75079668344c 100644
> --- a/include/linux/compiler-gcc.h
> +++ b/include/linux/compiler-gcc.h
> @@ -165,8 +165,13 @@
> #define __diag_str(s) __diag_str1(s)
> #define __diag(s) _Pragma(__diag_str(GCC diagnostic s))
>
> -#if GCC_VERSION >= 80000
> +#if GCC_VERSION >= 90000
> +#define __diag_GCC_8(s)
> +#define __diag_GCC_9(s) __diag(s)
> +#elif GCC_VERSION >= 80000
> #define __diag_GCC_8(s) __diag(s)
> +#define __diag_GCC_9(s)
> #else
> #define __diag_GCC_8(s)
> +#define __diag_GCC_9(s)
> #endif
> diff --git a/include/linux/syscalls.h b/include/linux/syscalls.h
> index 257cccba3062..a08059e1ccf4 100644
> --- a/include/linux/syscalls.h
> +++ b/include/linux/syscalls.h
> @@ -236,6 +236,8 @@ static inline int is_syscall_trace_event(struct trace_event_call *tp_event)
> __diag_push(); \
> __diag_ignore(GCC, 8, "-Wattribute-alias", \
> "Type aliasing is used to sanitize syscall arguments");\
> + __diag_ignore(GCC, 9, "-Wattribute-alias=1", \
> + "Type aliasing is used to sanitize syscall arguments");\
> asmlinkage long sys##name(__MAP(x,__SC_DECL,__VA_ARGS__)) \
> __attribute__((alias(__stringify(__se_sys##name)))); \
> ALLOW_ERROR_INJECTION(sys##name, ERRNO); \
> --
> 2.20.1
>