* [PATCH 2/2] [RFC] disable -Wattribute-alias warning for SYSCALL_DEFINEx()
[not found] <20171205153259.2522368-1-arnd@arndb.de>
@ 2017-12-05 16:06 ` Arnd Bergmann
2018-06-11 21:19 ` Stafford Horne
0 siblings, 1 reply; 2+ messages in thread
From: Arnd Bergmann @ 2017-12-05 16:06 UTC (permalink / raw)
To: linux-kbuild
Cc: Michal Marek, Masahiro Yamada, Douglas Anderson, Al Viro,
Heiko Carstens, Mauro Carvalho Chehab, Matthew Wilcox,
Matthias Kaehlcke, Arnd Bergmann, Deepa Dinamani, Thomas Gleixner,
Frederic Weisbecker, Stephan Mueller, David S. Miller,
Yonghong Song, Thomas Garnier, David Howells, linux-kernel,
linux-api
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.
Link: https://gcc.gnu.org/bugzilla/show_bug.cgi?id=82435
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
---
include/linux/compat.h | 7 ++++++-
include/linux/syscalls.h | 3 +++
2 files changed, 9 insertions(+), 1 deletion(-)
diff --git a/include/linux/compat.h b/include/linux/compat.h
index 1165036d091f..27b4a429df77 100644
--- a/include/linux/compat.h
+++ b/include/linux/compat.h
@@ -49,14 +49,19 @@
COMPAT_SYSCALL_DEFINEx(6, _##name, __VA_ARGS__)
#define COMPAT_SYSCALL_DEFINEx(x, name, ...) \
+ __diag_push(); \
+ __diag_ignore(GCC_8, "-Wattribute-alias"); \
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__));\
asmlinkage long compat_SyS##name(__MAP(x,__SC_LONG,__VA_ARGS__));\
asmlinkage long compat_SyS##name(__MAP(x,__SC_LONG,__VA_ARGS__))\
{ \
- return C_SYSC##name(__MAP(x,__SC_DELOUSE,__VA_ARGS__)); \
+ long ret = C_SYSC##name(__MAP(x,__SC_DELOUSE,__VA_ARGS__));\
+ __MAP(x,__SC_TEST,__VA_ARGS__); \
+ return ret; \
} \
+ __diag_pop(); \
static inline long C_SYSC##name(__MAP(x,__SC_DECL,__VA_ARGS__))
#ifdef CONFIG_COMPAT
diff --git a/include/linux/syscalls.h b/include/linux/syscalls.h
index 4df16a70b0d7..dcf6ceabda44 100644
--- a/include/linux/syscalls.h
+++ b/include/linux/syscalls.h
@@ -208,6 +208,8 @@ static inline int is_syscall_trace_event(struct trace_event_call *tp_event)
#define __PROTECT(...) asmlinkage_protect(__VA_ARGS__)
#define __SYSCALL_DEFINEx(x, name, ...) \
+ __diag_push(); \
+ __diag_ignore(GCC_8, "-Wattribute-alias"); \
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 +221,7 @@ static inline int is_syscall_trace_event(struct trace_event_call *tp_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__))
/*
--
2.9.0
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