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- From: Arnd Bergmann <[email protected]>
- Date: Tue, 19 Jun 2018 13:14:57 -0700
- Subject: [PATCH] disable -Wattribute-alias warning for SYSCALL_DEFINEx()
- gcc-8 warns for every single definition of a system call entry
- point, e.g.:
- include/linux/compat.h:56:18: error: 'compat_sys_rt_sigprocmask' alias between functions of incompatible types 'long int(int, compat_sigset_t *, compat_sigset_t *, compat_size_t)' {aka 'long int(int, struct <anonymous> *, struct <anonymous> *, unsigned int)'} and 'long int(long int, long int, long int, long int)' [-Werror=attribute-alias]
- asmlinkage long compat_sys##name(__MAP(x,__SC_DECL,__VA_ARGS__))\
- ^~~~~~~~~~
- include/linux/compat.h:45:2: note: in expansion of macro 'COMPAT_SYSCALL_DEFINEx'
- COMPAT_SYSCALL_DEFINEx(4, _##name, __VA_ARGS__)
- ^~~~~~~~~~~~~~~~~~~~~~
- kernel/signal.c:2601:1: note: in expansion of macro 'COMPAT_SYSCALL_DEFINE4'
- COMPAT_SYSCALL_DEFINE4(rt_sigprocmask, int, how, compat_sigset_t __user *, nset,
- ^~~~~~~~~~~~~~~~~~~~~~
- include/linux/compat.h:60:18: note: aliased declaration here
- asmlinkage long compat_SyS##name(__MAP(x,__SC_LONG,__VA_ARGS__))\
- ^~~~~~~~~~
- The new warning seems reasonable in principle, but it doesn't
- help us here, since we rely on the type mismatch to sanitize the
- system call arguments. After I reported this as GCC PR82435, a new
- -Wno-attribute-alias option was added that could be used to turn the
- warning off globally on the command line, but I'd prefer to do it a
- little more fine-grained.
- Interestingly, turning a warning off and on again inside of
- a single macro doesn't always work, in this case I had to add
- an extra statement inbetween and decided to copy the __SC_TEST
- one from the native syscall to the compat syscall macro. See
- https://gcc.gnu.org/bugzilla/show_bug.cgi?id=83256 for more details
- about this.
- [[email protected]:
- - Rebase atop current master.
- - Split GCC & version arguments to __diag_ignore() in order to match
- changes to the preceding patch.
- - Add the comment argument to match the preceding patch.]
- Link: https://gcc.gnu.org/bugzilla/show_bug.cgi?id=82435
- Signed-off-by: Arnd Bergmann <[email protected]>
- Signed-off-by: Paul Burton <[email protected]>
- Tested-by: Christophe Leroy <[email protected]>
- Tested-by: Stafford Horne <[email protected]>
- Signed-off-by: Masahiro Yamada <[email protected]>
- ---
- --- a/include/linux/compat.h
- +++ b/include/linux/compat.h
- @@ -48,6 +48,9 @@
- COMPAT_SYSCALL_DEFINEx(6, _##name, __VA_ARGS__)
-
- #define COMPAT_SYSCALL_DEFINEx(x, name, ...) \
- + __diag_push(); \
- + __diag_ignore(GCC, 8, "-Wattribute-alias", \
- + "Type aliasing is used to sanitize syscall arguments");\
- asmlinkage long compat_sys##name(__MAP(x,__SC_DECL,__VA_ARGS__))\
- __attribute__((alias(__stringify(compat_SyS##name)))); \
- static inline long C_SYSC##name(__MAP(x,__SC_DECL,__VA_ARGS__));\
- @@ -56,6 +59,7 @@
- { \
- return C_SYSC##name(__MAP(x,__SC_DELOUSE,__VA_ARGS__)); \
- } \
- + __diag_pop(); \
- static inline long C_SYSC##name(__MAP(x,__SC_DECL,__VA_ARGS__))
-
- #ifndef compat_user_stack_pointer
- --- a/include/linux/syscalls.h
- +++ b/include/linux/syscalls.h
- @@ -208,6 +208,9 @@ static inline int is_syscall_trace_event
-
- #define __PROTECT(...) asmlinkage_protect(__VA_ARGS__)
- #define __SYSCALL_DEFINEx(x, name, ...) \
- + __diag_push(); \
- + __diag_ignore(GCC, 8, "-Wattribute-alias", \
- + "Type aliasing is used to sanitize syscall arguments");\
- asmlinkage long sys##name(__MAP(x,__SC_DECL,__VA_ARGS__)) \
- __attribute__((alias(__stringify(SyS##name)))); \
- static inline long SYSC##name(__MAP(x,__SC_DECL,__VA_ARGS__)); \
- @@ -219,6 +222,7 @@ static inline int is_syscall_trace_event
- __PROTECT(x, ret,__MAP(x,__SC_ARGS,__VA_ARGS__)); \
- return ret; \
- } \
- + __diag_pop(); \
- static inline long SYSC##name(__MAP(x,__SC_DECL,__VA_ARGS__))
-
- /*
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