diff mbox series

[2/3] disable -Wattribute-alias warning for SYSCALL_DEFINEx()

Message ID 20180616005323.7938-3-paul.burton@mips.com (mailing list archive)
State Not Applicable
Headers show
Series Resolve -Wattribute-alias warnings from SYSCALL_DEFINEx() | expand

Commit Message

Paul Burton June 16, 2018, 12:53 a.m. UTC 
From: Arnd Bergmann <arnd@arndb.de>

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>
Cc: Michal Marek <michal.lkml@markovi.net>
Cc: Masahiro Yamada <yamada.masahiro@socionext.com>
Cc: Douglas Anderson <dianders@chromium.org>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: Heiko Carstens <heiko.carstens@de.ibm.com>
Cc: Mauro Carvalho Chehab <mchehab@kernel.org>
Cc: Matthew Wilcox <matthew@wil.cx>
Cc: Matthias Kaehlcke <mka@chromium.org>
Cc: Arnd Bergmann <arnd@arndb.de>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Josh Poimboeuf <jpoimboe@redhat.com>
Cc: Kees Cook <keescook@chromium.org>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Gideon Israel Dsouza <gidisrael@gmail.com>
Cc: Christophe Leroy <christophe.leroy@c-s.fr>
Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Michael Ellerman <mpe@ellerman.id.au>
Cc: Stafford Horne <shorne@gmail.com>
Cc: Khem Raj <raj.khem@gmail.com>
Cc: He Zhe <zhe.he@windriver.com>
Cc: linux-kbuild@vger.kernel.org
Cc: linux-kernel@vger.kernel.org
Cc: linux-mips@linux-mips.org
Cc: linuxppc-dev@lists.ozlabs.org
---

 include/linux/compat.h   | 8 +++++++-
 include/linux/syscalls.h | 4 ++++
 2 files changed, 11 insertions(+), 1 deletion(-)

Comments

Christophe Leroy June 18, 2018, 7:01 a.m. UTC | #1 
Le 16/06/2018 à 02:53, Paul Burton a écrit :
> From: Arnd Bergmann <arnd@arndb.de>
> 
> 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>
> Cc: Michal Marek <michal.lkml@markovi.net>
> Cc: Masahiro Yamada <yamada.masahiro@socionext.com>
> Cc: Douglas Anderson <dianders@chromium.org>
> Cc: Al Viro <viro@zeniv.linux.org.uk>
> Cc: Heiko Carstens <heiko.carstens@de.ibm.com>
> Cc: Mauro Carvalho Chehab <mchehab@kernel.org>
> Cc: Matthew Wilcox <matthew@wil.cx>
> Cc: Matthias Kaehlcke <mka@chromium.org>
> Cc: Arnd Bergmann <arnd@arndb.de>
> Cc: Ingo Molnar <mingo@kernel.org>
> Cc: Josh Poimboeuf <jpoimboe@redhat.com>
> Cc: Kees Cook <keescook@chromium.org>
> Cc: Andrew Morton <akpm@linux-foundation.org>
> Cc: Thomas Gleixner <tglx@linutronix.de>
> Cc: Gideon Israel Dsouza <gidisrael@gmail.com>
> Cc: Christophe Leroy <christophe.leroy@c-s.fr>
> Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
> Cc: Paul Mackerras <paulus@samba.org>
> Cc: Michael Ellerman <mpe@ellerman.id.au>
> Cc: Stafford Horne <shorne@gmail.com>
> Cc: Khem Raj <raj.khem@gmail.com>
> Cc: He Zhe <zhe.he@windriver.com>
> Cc: linux-kbuild@vger.kernel.org
> Cc: linux-kernel@vger.kernel.org
> Cc: linux-mips@linux-mips.org
> Cc: linuxppc-dev@lists.ozlabs.org

Tested-by: Christophe Leroy <christophe.leroy@c-s.fr>


> ---
> 
>   include/linux/compat.h   | 8 +++++++-
>   include/linux/syscalls.h | 4 ++++
>   2 files changed, 11 insertions(+), 1 deletion(-)
> 
> diff --git a/include/linux/compat.h b/include/linux/compat.h
> index b1a5562b3215..c68acc47da57 100644
> --- a/include/linux/compat.h
> +++ b/include/linux/compat.h
> @@ -72,6 +72,9 @@
>    */
>   #ifndef COMPAT_SYSCALL_DEFINEx
>   #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__));	\
>   	asmlinkage long compat_sys##name(__MAP(x,__SC_DECL,__VA_ARGS__))	\
>   		__attribute__((alias(__stringify(__se_compat_sys##name))));	\
> @@ -80,8 +83,11 @@
>   	asmlinkage long __se_compat_sys##name(__MAP(x,__SC_LONG,__VA_ARGS__));	\
>   	asmlinkage long __se_compat_sys##name(__MAP(x,__SC_LONG,__VA_ARGS__))	\
>   	{									\
> -		return __do_compat_sys##name(__MAP(x,__SC_DELOUSE,__VA_ARGS__));\
> +		long ret = __do_compat_sys##name(__MAP(x,__SC_DELOUSE,__VA_ARGS__));\
> +		__MAP(x,__SC_TEST,__VA_ARGS__);					\
> +		return ret;							\
>   	}									\
> +	__diag_pop();								\
>   	static inline long __do_compat_sys##name(__MAP(x,__SC_DECL,__VA_ARGS__))
>   #endif /* COMPAT_SYSCALL_DEFINEx */
>   
> diff --git a/include/linux/syscalls.h b/include/linux/syscalls.h
> index 73810808cdf2..a368a68cb667 100644
> --- a/include/linux/syscalls.h
> +++ b/include/linux/syscalls.h
> @@ -231,6 +231,9 @@ static inline int is_syscall_trace_event(struct trace_event_call *tp_event)
>    */
>   #ifndef __SYSCALL_DEFINEx
>   #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(__se_sys##name))));	\
>   	ALLOW_ERROR_INJECTION(sys##name, ERRNO);			\
> @@ -243,6 +246,7 @@ 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 __do_sys##name(__MAP(x,__SC_DECL,__VA_ARGS__))
>   #endif /* __SYSCALL_DEFINEx */
>   
>
diff mbox series

Patch

diff --git a/include/linux/compat.h b/include/linux/compat.h
index b1a5562b3215..c68acc47da57 100644
--- a/include/linux/compat.h
+++ b/include/linux/compat.h
@@ -72,6 +72,9 @@ 
  */
 #ifndef COMPAT_SYSCALL_DEFINEx
 #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__));	\
 	asmlinkage long compat_sys##name(__MAP(x,__SC_DECL,__VA_ARGS__))	\
 		__attribute__((alias(__stringify(__se_compat_sys##name))));	\
@@ -80,8 +83,11 @@ 
 	asmlinkage long __se_compat_sys##name(__MAP(x,__SC_LONG,__VA_ARGS__));	\
 	asmlinkage long __se_compat_sys##name(__MAP(x,__SC_LONG,__VA_ARGS__))	\
 	{									\
-		return __do_compat_sys##name(__MAP(x,__SC_DELOUSE,__VA_ARGS__));\
+		long ret = __do_compat_sys##name(__MAP(x,__SC_DELOUSE,__VA_ARGS__));\
+		__MAP(x,__SC_TEST,__VA_ARGS__);					\
+		return ret;							\
 	}									\
+	__diag_pop();								\
 	static inline long __do_compat_sys##name(__MAP(x,__SC_DECL,__VA_ARGS__))
 #endif /* COMPAT_SYSCALL_DEFINEx */
 
diff --git a/include/linux/syscalls.h b/include/linux/syscalls.h
index 73810808cdf2..a368a68cb667 100644
--- a/include/linux/syscalls.h
+++ b/include/linux/syscalls.h
@@ -231,6 +231,9 @@  static inline int is_syscall_trace_event(struct trace_event_call *tp_event)
  */
 #ifndef __SYSCALL_DEFINEx
 #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(__se_sys##name))));	\
 	ALLOW_ERROR_INJECTION(sys##name, ERRNO);			\
@@ -243,6 +246,7 @@  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 __do_sys##name(__MAP(x,__SC_DECL,__VA_ARGS__))
 #endif /* __SYSCALL_DEFINEx */