Re: [PATCH] Disable -Wattribute-alias for clang-23 and newer

[Nathan Chancellor <nathan@kernel.org>]

On Fri, May 15, 2026 at 07:35:18PM +0900, Nathan Chancellor wrote:
> Clang recently added support for -Wattribute-alias [1], which results in
> the same warnings that necessitated commit bee20031772a ("disable
> -Wattribute-alias warning for SYSCALL_DEFINEx()") for GCC.
> 
>   kernel/time/itimer.c:325:1: error: alias and aliasee have different types 'long (unsigned int)' and 'long (typeof (__builtin_choose_expr((__builtin_types_compatible_p(typeof ((unsigned int)0), typeof (0LL)) || __builtin_types_compatible_p(typeof ((unsigned int)0), typeof (0ULL))), 0LL, 0L)))' (aka 'long (long)') [-Werror,-Wattribute-alias]
>     325 | SYSCALL_DEFINE1(alarm, unsigned int, seconds)
>         | ^
>   include/linux/syscalls.h:225:36: note: expanded from macro 'SYSCALL_DEFINE1'
>     225 | #define SYSCALL_DEFINE1(name, ...) SYSCALL_DEFINEx(1, _##name, __VA_ARGS__)
>         |                                    ^
>   include/linux/syscalls.h:236:2: note: expanded from macro 'SYSCALL_DEFINEx'
>     236 |         __SYSCALL_DEFINEx(x, sname, __VA_ARGS__)
>         |         ^
>   include/linux/syscalls.h:251:18: note: expanded from macro '__SYSCALL_DEFINEx'
>     251 |                 __attribute__((alias(__stringify(__se_sys##name))));    \
>         |                                ^
>   kernel/time/itimer.c:325:1: note: aliasee is declared here
>   include/linux/syscalls.h:225:36: note: expanded from macro 'SYSCALL_DEFINE1'
>     225 | #define SYSCALL_DEFINE1(name, ...) SYSCALL_DEFINEx(1, _##name, __VA_ARGS__)
>         |                                    ^
>   include/linux/syscalls.h:236:2: note: expanded from macro 'SYSCALL_DEFINEx'
>     236 |         __SYSCALL_DEFINEx(x, sname, __VA_ARGS__)
>         |         ^
>   include/linux/syscalls.h:255:18: note: expanded from macro '__SYSCALL_DEFINEx'
>     255 |         asmlinkage long __se_sys##name(__MAP(x,__SC_LONG,__VA_ARGS__))  \
>         |                         ^
>   <scratch space>:16:1: note: expanded from here
>      16 | __se_sys_alarm
>         | ^
> 
> Disable the warnings in the same way for clang-23 and newer.
> 
> Cc: stable@vger.kernel.org
> Closes: https://github.com/ClangBuiltLinux/linux/issues/2163
> Link: https://github.com/llvm/llvm-project/commit/40da6920a0d71d49dfa2392b09153600b0759f5e [1]
> Signed-off-by: Nathan Chancellor <nathan@kernel.org>
> ---
> I plan to take this via my clang-fixes tree for 7.1.
> ---
>  arch/riscv/include/asm/syscall_wrapper.h | 2 ++
>  include/linux/compat.h                   | 2 ++
>  include/linux/compiler-clang.h           | 6 ++++++
>  include/linux/syscalls.h                 | 2 ++
>  4 files changed, 12 insertions(+)
> 
> diff --git a/arch/riscv/include/asm/syscall_wrapper.h b/arch/riscv/include/asm/syscall_wrapper.h
> index ac80216549ff..366a5354caa5 100644
> --- a/arch/riscv/include/asm/syscall_wrapper.h
> +++ b/arch/riscv/include/asm/syscall_wrapper.h
> @@ -32,6 +32,8 @@ asmlinkage long __riscv_sys_ni_syscall(const struct pt_regs *);
>  	__diag_push();									\
>  	__diag_ignore(GCC, 8, "-Wattribute-alias",					\
>  			"Type aliasing is used to sanitize syscall arguments");		\
> +	__diag_ignore(clang, 23, "-Wattribute-alias",					\
> +			"Type aliasing is used to sanitize syscall arguments");		\
>  	static long __se_##prefix##name(ulong, ulong, ulong, ulong, ulong, ulong, 	\
>  					ulong)						\
>  			__attribute__((alias(__stringify(___se_##prefix##name))));	\
> diff --git a/include/linux/compat.h b/include/linux/compat.h
> index 56cebaff0c91..a1ce6d559db9 100644
> --- a/include/linux/compat.h
> +++ b/include/linux/compat.h
> @@ -72,6 +72,8 @@
>  	__diag_push();								\
>  	__diag_ignore(GCC, 8, "-Wattribute-alias",				\
>  		      "Type aliasing is used to sanitize syscall arguments");\
> +	__diag_ignore(clang, 23, "-Wattribute-alias",				\
> +		      "Type aliasing is used to sanitize syscall arguments");\
>  	asmlinkage long compat_sys##name(__MAP(x,__SC_DECL,__VA_ARGS__))	\
>  		__attribute__((alias(__stringify(__se_compat_sys##name))));	\
>  	ALLOW_ERROR_INJECTION(compat_sys##name, ERRNO);				\
> diff --git a/include/linux/compiler-clang.h b/include/linux/compiler-clang.h
> index e1123dd28486..527e4e136020 100644
> --- a/include/linux/compiler-clang.h
> +++ b/include/linux/compiler-clang.h
> @@ -131,6 +131,12 @@
>  #define __diag_str(s)		__diag_str1(s)
>  #define __diag(s)		_Pragma(__diag_str(clang diagnostic s))
>  
> +#if CONFIG_CLANG_VERSION >= 230000
> +#define __diag_clang_23(s)	__diag(s)
> +#else
> +#define __diag_clang_23(s)
> +#endif
> +
>  #define __diag_clang_13(s)	__diag(s)
>  
>  #define __diag_ignore_all(option, comment) \
> diff --git a/include/linux/syscalls.h b/include/linux/syscalls.h
> index f5639d5ac331..97e3411b49d2 100644
> --- a/include/linux/syscalls.h
> +++ b/include/linux/syscalls.h
> @@ -247,6 +247,8 @@ 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(clang, 23, "-Wattribute-alias",			\
> +		      "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);			\

The kbuild test robot pointed out that I need

diff --git a/include/linux/compiler_types.h b/include/linux/compiler_types.h
index e8fd77593b68..369966598a2c 100644
--- a/include/linux/compiler_types.h
+++ b/include/linux/compiler_types.h
@@ -711,6 +711,10 @@ struct ftrace_likely_data {
 #define __diag_GCC(version, severity, string)
 #endif
 
+#ifndef __diag_clang
+#define __diag_clang(version, severity, string)
+#endif
+
 #define __diag_push()	__diag(push)
 #define __diag_pop()	__diag(pop)
 
--

for this to build properly with GCC, which I will fold in.

-- 
Cheers,
Nathan

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