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Re: [PATCH v4 19/28] arm64/sve: ptrace and ELF coredump support
- From: Catalin Marinas <catalin dot marinas at arm dot com>
- To: Dave Martin <Dave dot Martin at arm dot com>
- Cc: linux-arm-kernel at lists dot infradead dot org, linux-arch at vger dot kernel dot org, Okamoto Takayuki <tokamoto at jp dot fujitsu dot com>, libc-alpha at sourceware dot org, Ard Biesheuvel <ard dot biesheuvel at linaro dot org>, Szabolcs Nagy <szabolcs dot nagy at arm dot com>, Will Deacon <will dot deacon at arm dot com>, Alan Hayward <alan dot hayward at arm dot com>, Alex Bennée <alex dot bennee at linaro dot org>, kvmarm at lists dot cs dot columbia dot edu
- Date: Fri, 27 Oct 2017 14:04:11 +0100
- Subject: Re: [PATCH v4 19/28] arm64/sve: ptrace and ELF coredump support
- Authentication-results: sourceware.org; auth=none
- References: <1509101470-7881-1-git-send-email-Dave.Martin@arm.com> <1509101470-7881-20-git-send-email-Dave.Martin@arm.com>
On Fri, Oct 27, 2017 at 11:51:01AM +0100, Dave P Martin wrote:
> This patch defines and implements a new regset NT_ARM_SVE, which
> describes a thread's SVE register state. This allows a debugger to
> manipulate the SVE state, as well as being included in ELF
> coredumps for post-mortem debugging.
>
> Because the regset size and layout are dependent on the thread's
> current vector length, it is not possible to define a C struct to
> describe the regset contents as is done for existing regsets.
> Instead, and for the same reasons, NT_ARM_SVE is based on the
> freeform variable-layout approach used for the SVE signal frame.
>
> Additionally, to reduce debug overhead when debugging threads that
> might or might not have live SVE register state, NT_ARM_SVE may be
> presented in one of two different formats: the old struct
> user_fpsimd_state format is embedded for describing the state of a
> thread with no live SVE state, whereas a new variable-layout
> structure is embedded for describing live SVE state. This avoids a
> debugger needing to poll NT_PRFPREG in addition to NT_ARM_SVE, and
> allows existing userspace code to handle the non-SVE case without
> too much modification.
>
> For this to work, NT_ARM_SVE is defined with a fixed-format header
> of type struct user_sve_header, which the recipient can use to
> figure out the content, size and layout of the reset of the regset.
> Accessor macros are defined to allow the vector-length-dependent
> parts of the regset to be manipulated.
>
> Signed-off-by: Alan Hayward <alan.hayward@arm.com>
> Signed-off-by: Dave Martin <Dave.Martin@arm.com>
> Cc: Alex Bennée <alex.bennee@linaro.org>
> Cc: Okamoto Takayuki <tokamoto@jp.fujitsu.com>
Reviewed-by: Catalin Marinas <catalin.marinas@arm.com>