OpenWrt – Rev 1
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From: Arnd Bergmann <arnd@arndb.de>
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.
[paul.burton@mips.com:
- 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 <arnd@arndb.de>
Signed-off-by: Paul Burton <paul.burton@mips.com>
Tested-by: Christophe Leroy <christophe.leroy@c-s.fr>
Tested-by: Stafford Horne <shorne@gmail.com>
Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>
---
--- 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__))
/*