Re: [PATCH] powerpc64: use a type for mcontext_t regs field

[Rich Felker <dalias@libc.org>]

On Tue, Feb 12, 2019 at 09:35:22AM -0600, A. Wilcox wrote:
> GCC Go dereferences `regs` for `nip`.  Without this change, compilation
> fails with the following message:
> 
> .../../../libgo/runtime/go-signal.c: In function ‘getSiginfo’:
> .../../../libgo/runtime/go-signal.c:225:56: warning: dereferencing ‘void *’ pointer
>   ret.sigpc = ((ucontext_t*)(context))->uc_mcontext.regs->nip;
>                                                         ^~
> .../../../libgo/runtime/go-signal.c:225:56: error: request for member ‘nip’ in something not a structure or union
> ---
>  arch/powerpc64/bits/signal.h | 4 +++-
>  1 file changed, 3 insertions(+), 1 deletion(-)
> 
> diff --git a/arch/powerpc64/bits/signal.h b/arch/powerpc64/bits/signal.h
> index 34693a68..6736c69a 100644
> --- a/arch/powerpc64/bits/signal.h
> +++ b/arch/powerpc64/bits/signal.h
> @@ -8,6 +8,8 @@
>  
>  #if defined(_GNU_SOURCE) || defined(_BSD_SOURCE)
>  
> +#include <bits/user.h>
> +

This is almost surely not right. You can never use a bits/* header
except from the corresponding public header that includes it. They do
not have multiple-inclusion guards and are not designed to be usable
independently. And including sys/user.h is also almost surely wrong
since it's a problematic header you don't want getting included
(conflicts with linux/*.h stuff).

>  typedef unsigned long greg_t, gregset_t[48];
>  
>  typedef struct {
> @@ -29,7 +31,7 @@ typedef struct sigcontext {
>  	int _pad0;
>  	unsigned long handler;
>  	unsigned long oldmask;
> -	void *regs;
> +	struct pt_regs *regs;
>  	gregset_t gp_regs;
>  	fpregset_t fp_regs;
>  	vrregset_t *v_regs;
> -- 
> 2.19.2

Do you know if there's a reason Go is trying to use this regs member
rather than gp_regs? I think that's the real issue here.

Rich