On Thu, Jun 15, 2017 at 03:03:42PM +0100, Dave P Martin wrote:
> --- a/arch/arm64/include/uapi/asm/sigcontext.h
> +++ b/arch/arm64/include/uapi/asm/sigcontext.h
> @@ -41,9 +41,10 @@ struct sigcontext {
> *
> * 0x210 fpsimd_context
> * 0x10 esr_context
> + * 0x20 extra_context (optional)
> * 0x10 terminator (null _aarch64_ctx)
> *
> - * 0xdd0 (reserved for future allocation)
> + * 0xdb0 (reserved for future allocation)
> *
> * New records that can exceed this space need to be opt-in for userspace, so
> * that an expanded signal frame is not generated unexpectedly. The mechanism
> @@ -80,4 +81,39 @@ struct esr_context {
> __u64 esr;
> };
>
> +/*
> + * extra_context: describes extra space in the signal frame for
> + * additional structures that don't fit in sigcontext.__reserved[].
> + *
> + * Note:
> + *
> + * 1) fpsimd_context, esr_context and extra_context must be placed in
> + * sigcontext.__reserved[] if present. They cannot be placed in the
> + * extra space. Any other record can be placed either in the extra
> + * space or in sigcontext.__reserved[], unless otherwise specified in
> + * this file.
> + *
> + * 2) There must not be more than one extra_context.
> + *
> + * 3) If extra_context is present, it must be followed immediately in
> + * sigcontext.__reserved[] by the terminating null _aarch64_ctx.
> + *
> + * 4) The extra space to which data points must start at the first
> + * 16-byte aligned address immediately after the terminating null
> + * _aarch64_ctx that follows the extra_context structure in
> + * __reserved[]. The extra space may overrun the end of __reserved[],
> + * as indicated by a sufficiently large value for the size field.
> + *
> + * 5) The extra space must itself be terminated with a null
> + * _aarch64_ctx.
> + */
> +#define EXTRA_MAGIC 0x45585401
> +
> +struct extra_context {
> + struct _aarch64_ctx head;
> + void __user *data; /* 16-byte aligned pointer to extra space */
> + __u32 size; /* size in bytes of the extra space */
> + __u32 __reserved[3];
> +};
Some more thoughts on the type of "data" above. It's the first time we
introduce pointers in sigcontext and wonder whether __u64 would make
more sense (invariable size with the ABI).
Also for discussion - whether using an offset vs absolute address would
be better.
--
Catalin
