[PATCH v2 1/3] signal: Add FPE_FLTUNK si_code for undiagnosable fp exceptions

[Eric W. Biederman]

Dave Martin <Dave.Martin at arm.com> writes:

> Some architectures cannot always report accurately what kind of
> floating-point exception triggered a floating-point exception trap.
>
> This can occur with fp exceptions occurring on lanes in a vector
> instruction on arm64 for example.
>
> Rather than have every architecture come up with its own way of
> describing such a condition, this patch adds a common FPE_FLTUNK
> si_code value to report that an fp exception caused a trap but we
> cannot be certain which kind of fp exception it was.
>
> Signed-off-by: Dave Martin <Dave.Martin at arm.com>

Reviewed-by: "Eric W. Biederman" <ebiederm at xmission.com>

> --
>
> Changes since v1:
>
> Reported by James Morse:
>
>  * Bump NSIGFPE BUILD_BUG_ON() check for x86 compat.
>
>    FPE_FLTUNK does not current have any implications for x86, since it
>    is not currently used and has no implications for the way siginfo
>    is populated.
> ---
>  arch/x86/kernel/signal_compat.c    | 2 +-
>  include/uapi/asm-generic/siginfo.h | 3 ++-
>  2 files changed, 3 insertions(+), 2 deletions(-)
>
> diff --git a/arch/x86/kernel/signal_compat.c b/arch/x86/kernel/signal_compat.c
> index ac057f9..954ad99 100644
> --- a/arch/x86/kernel/signal_compat.c
> +++ b/arch/x86/kernel/signal_compat.c
> @@ -26,7 +26,7 @@ static inline void signal_compat_build_tests(void)
>  	 * new fields are handled in copy_siginfo_to_user32()!
>  	 */
>  	BUILD_BUG_ON(NSIGILL  != 11);
> -	BUILD_BUG_ON(NSIGFPE  != 13);
> +	BUILD_BUG_ON(NSIGFPE  != 14);
>  	BUILD_BUG_ON(NSIGSEGV != 4);
>  	BUILD_BUG_ON(NSIGBUS  != 5);
>  	BUILD_BUG_ON(NSIGTRAP != 4);

For other reviewers.  This bug on exists to ensure people remember to
update the helper functions when new fields are added to struct siginfo.
As new fields usually come with new si_codes.  There are no fields
added so this is sufficient.

> diff --git a/include/uapi/asm-generic/siginfo.h b/include/uapi/asm-generic/siginfo.h
> index 85dc965..10304de 100644
> --- a/include/uapi/asm-generic/siginfo.h
> +++ b/include/uapi/asm-generic/siginfo.h
> @@ -229,7 +229,8 @@ typedef struct siginfo {
>  # define __FPE_INVASC	12	/* invalid ASCII digit */
>  # define __FPE_INVDEC	13	/* invalid decimal digit */
>  #endif
> -#define NSIGFPE		13
> +#define FPE_FLTUNK	14	/* undiagnosed floating-point exception */
> +#define NSIGFPE		14
>  
>  /*
>   * SIGSEGV si_codes