Disable -Wattribute-alias for clang-23 and newer

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. Disable the
warning about unknown warning options to avoid breaking the build for
versions of clang-23 that do not have -Wattribute-alias, such as ones
deployed by vendors like Android or CI systems or when bisecting LLVM
between llvmorg-23-init and release/23.x.

Cc: stable@vger.kernel.org
Closes: https://github.com/ClangBuiltLinux/linux/issues/2163
Link: https://github.com/llvm/llvm-project/commit/40da6920a0d71d49dfa2392b09153600b0759f5e [1]
Link: https://patch.msgid.link/20260515-syscall-disable-attribute-alias-for-clang-v1-1-9a9d95d41df6@kernel.org
Signed-off-by: Nathan Chancellor <nathan@kernel.org>

4 files changed, 18 insertions, 0 deletions

diff --git a/include/linux/compat.h b/include/linux/compat.h
index 56cebaff0c91..8da0a15c95f4 100644
--- a/include/linux/compat.h
+++ b/include/linux/compat.h
@@ -72,6 +72,10 @@
 	__diag_push();								\
 	__diag_ignore(GCC, 8, "-Wattribute-alias",				\
 		      "Type aliasing is used to sanitize syscall arguments");\
+	__diag_ignore(clang, 23, "-Wunknown-warning-option",			\
+		      "Avoid breaking versions without -Wattribute-alias");	\
+	__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/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)
 
diff --git a/include/linux/syscalls.h b/include/linux/syscalls.h
index f5639d5ac331..4fb7291f54b6 100644
--- a/include/linux/syscalls.h
+++ b/include/linux/syscalls.h
@@ -247,6 +247,10 @@ 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, "-Wunknown-warning-option",		\
+		      "Avoid breaking versions without -Wattribute-alias");\
+	__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);			\