target/linux/generic/backport-4.19/013-disable-Wattribute-alias-warning-for-SYSCALL_DEFINEx.patch

   1 From: Arnd Bergmann <arnd@arndb.de>
   2 Date: Tue, 19 Jun 2018 13:14:57 -0700
   3 Subject: [PATCH] disable -Wattribute-alias warning for SYSCALL_DEFINEx()
   4
   5 gcc-8 warns for every single definition of a system call entry
   6 point, e.g.:
   7
   8 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]
   9   asmlinkage long compat_sys##name(__MAP(x,__SC_DECL,__VA_ARGS__))\
  10                   ^~~~~~~~~~
  11 include/linux/compat.h:45:2: note: in expansion of macro 'COMPAT_SYSCALL_DEFINEx'
  12   COMPAT_SYSCALL_DEFINEx(4, _##name, __VA_ARGS__)
  13   ^~~~~~~~~~~~~~~~~~~~~~
  14 kernel/signal.c:2601:1: note: in expansion of macro 'COMPAT_SYSCALL_DEFINE4'
  15  COMPAT_SYSCALL_DEFINE4(rt_sigprocmask, int, how, compat_sigset_t __user *, nset,
  16  ^~~~~~~~~~~~~~~~~~~~~~
  17 include/linux/compat.h:60:18: note: aliased declaration here
  18   asmlinkage long compat_SyS##name(__MAP(x,__SC_LONG,__VA_ARGS__))\
  19                   ^~~~~~~~~~
  20
  21 The new warning seems reasonable in principle, but it doesn't
  22 help us here, since we rely on the type mismatch to sanitize the
  23 system call arguments. After I reported this as GCC PR82435, a new
  24 -Wno-attribute-alias option was added that could be used to turn the
  25 warning off globally on the command line, but I'd prefer to do it a
  26 little more fine-grained.
  27
  28 Interestingly, turning a warning off and on again inside of
  29 a single macro doesn't always work, in this case I had to add
  30 an extra statement inbetween and decided to copy the __SC_TEST
  31 one from the native syscall to the compat syscall macro.  See
  32 https://gcc.gnu.org/bugzilla/show_bug.cgi?id=83256 for more details
  33 about this.
  34
  35 [paul.burton@mips.com:
  36   - Rebase atop current master.
  37   - Split GCC & version arguments to __diag_ignore() in order to match
  38     changes to the preceding patch.
  39   - Add the comment argument to match the preceding patch.]
  40
  41 Link: https://gcc.gnu.org/bugzilla/show_bug.cgi?id=82435
  42 Signed-off-by: Arnd Bergmann <arnd@arndb.de>
  43 Signed-off-by: Paul Burton <paul.burton@mips.com>
  44 Tested-by: Christophe Leroy <christophe.leroy@c-s.fr>
  45 Tested-by: Stafford Horne <shorne@gmail.com>
  46 Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>
  47 ---
  48
  49 --- a/include/linux/compat.h
  50 +++ b/include/linux/compat.h
  51 @@ -48,6 +48,9 @@
  52         COMPAT_SYSCALL_DEFINEx(6, _##name, __VA_ARGS__)
  53
  54  #define COMPAT_SYSCALL_DEFINEx(x, name, ...)                           \
  55 +       __diag_push();                                                  \
  56 +       __diag_ignore(GCC, 8, "-Wattribute-alias",                      \
  57 +                     "Type aliasing is used to sanitize syscall arguments");\
  58         asmlinkage long compat_sys##name(__MAP(x,__SC_DECL,__VA_ARGS__))\
  59                 __attribute__((alias(__stringify(compat_SyS##name))));  \
  60         static inline long C_SYSC##name(__MAP(x,__SC_DECL,__VA_ARGS__));\
  61 @@ -56,6 +59,7 @@
  62         {                                                               \
  63                 return C_SYSC##name(__MAP(x,__SC_DELOUSE,__VA_ARGS__)); \
  64         }                                                               \
  65 +       __diag_pop();                                                   \
  66         static inline long C_SYSC##name(__MAP(x,__SC_DECL,__VA_ARGS__))
  67
  68  #ifndef compat_user_stack_pointer
  69 --- a/include/linux/syscalls.h
  70 +++ b/include/linux/syscalls.h
  71 @@ -208,6 +208,9 @@ static inline int is_syscall_trace_event
  72
  73  #define __PROTECT(...) asmlinkage_protect(__VA_ARGS__)
  74  #define __SYSCALL_DEFINEx(x, name, ...)                                        \
  75 +       __diag_push();                                                  \
  76 +       __diag_ignore(GCC, 8, "-Wattribute-alias",                      \
  77 +                     "Type aliasing is used to sanitize syscall arguments");\
  78         asmlinkage long sys##name(__MAP(x,__SC_DECL,__VA_ARGS__))       \
  79                 __attribute__((alias(__stringify(SyS##name))));         \
  80         static inline long SYSC##name(__MAP(x,__SC_DECL,__VA_ARGS__));  \
  81 @@ -219,6 +222,7 @@ static inline int is_syscall_trace_event
  82                 __PROTECT(x, ret,__MAP(x,__SC_ARGS,__VA_ARGS__));       \
  83                 return ret;                                             \
  84         }                                                               \
  85 +       __diag_pop();                                                   \
  86         static inline long SYSC##name(__MAP(x,__SC_DECL,__VA_ARGS__))
  87
  88  /*