Re: [PATCH] [stable 4.14] turn off -Wattribute-alias

[Greg KH <gregkh@linuxfoundation.org>]

On Thu, Jul 26, 2018 at 10:13:22AM +0200, Arnd Bergmann wrote:
> Starting with gcc-8.1, we get a warning about all system call definitions,
> which use an alias between functions with incompatible prototypes, e.g.:
> 
> In file included from ../mm/process_vm_access.c:19:
> ../include/linux/syscalls.h:211:18: warning: 'sys_process_vm_readv' alias between functions of incompatible types 'long int(pid_t,  const struct iovec *, long unsigned int,  const struct iovec *, long unsigned int,  long unsigned int)' {aka 'long int(int,  const struct iovec *, long unsigned int,  const struct iovec *, long unsigned int,  long unsigned int)'} and 'long int(long int,  long int,  long int,  long int,  long int,  long int)' [-Wattribute-alias]
>   asmlinkage long sys##name(__MAP(x,__SC_DECL,__VA_ARGS__)) \
>                   ^~~
> ../include/linux/syscalls.h:207:2: note: in expansion of macro '__SYSCALL_DEFINEx'
>   __SYSCALL_DEFINEx(x, sname, __VA_ARGS__)
>   ^~~~~~~~~~~~~~~~~
> ../include/linux/syscalls.h:201:36: note: in expansion of macro 'SYSCALL_DEFINEx'
>  #define SYSCALL_DEFINE6(name, ...) SYSCALL_DEFINEx(6, _##name, __VA_ARGS__)
>                                     ^~~~~~~~~~~~~~~
> ../mm/process_vm_access.c:300:1: note: in expansion of macro 'SYSCALL_DEFINE6'
>  SYSCALL_DEFINE6(process_vm_readv, pid_t, pid, const struct iovec __user *, lvec,
>  ^~~~~~~~~~~~~~~
> ../include/linux/syscalls.h:215:18: note: aliased declaration here
>   asmlinkage long SyS##name(__MAP(x,__SC_LONG,__VA_ARGS__)) \
>                   ^~~
> ../include/linux/syscalls.h:207:2: note: in expansion of macro '__SYSCALL_DEFINEx'
>   __SYSCALL_DEFINEx(x, sname, __VA_ARGS__)
>   ^~~~~~~~~~~~~~~~~
> ../include/linux/syscalls.h:201:36: note: in expansion of macro 'SYSCALL_DEFINEx'
>  #define SYSCALL_DEFINE6(name, ...) SYSCALL_DEFINEx(6, _##name, __VA_ARGS__)
>                                     ^~~~~~~~~~~~~~~
> ../mm/process_vm_access.c:300:1: note: in expansion of macro 'SYSCALL_DEFINE6'
>  SYSCALL_DEFINE6(process_vm_readv, pid_t, pid, const struct iovec __user *, lvec,
> 
> This is really noisy and does not indicate a real problem. In the latest
> mainline kernel, this was addressed by commit bee20031772a ("disable
> -Wattribute-alias warning for SYSCALL_DEFINEx()"), which seems too invasive
> to backport.

Too invasive?

Here's the diffstat:
	 include/linux/compat.h   |    8 +++++++-
	 include/linux/syscalls.h |    4 ++++
	 2 files changed, 11 insertions(+), 1 deletion(-)

That seems almost trivial to backport.  Did you try it and it caused
other problems?

Where ever possible, I always want to use the upstream commits.

thanks,

greg k-h