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Re: [RFC PATCH 0/2] ARM: Fix unparseable signal frame with CONFIG_IWMMXT
- From: Russell King - ARM Linux <linux at armlinux dot org dot uk>
- To: Dave Martin <Dave dot Martin at arm dot com>
- Cc: linux-arm-kernel at lists dot infradead dot org, Edmund Grimley-Evans <Edmund dot Grimley-Evans at arm dot com>, libc-alpha at sourceware dot org, gdb at sourceware dot org
- Date: Mon, 26 Jun 2017 11:13:04 +0100
- Subject: Re: [RFC PATCH 0/2] ARM: Fix unparseable signal frame with CONFIG_IWMMXT
- Authentication-results: sourceware.org; auth=none
- References: <1498059983-13438-1-git-send-email-Dave.Martin@arm.com>
On Wed, Jun 21, 2017 at 04:46:01PM +0100, Dave Martin wrote:
> In kernels with CONFIG_IWMMXT=y running on non-iWMMXt hardware, the
> signal frame can be left partially uninitialised in such a way
> that userspace cannot parse uc_regspace safely. In particular,
> this means that the VFP registers cannot be located reliably in the
> signal frame when a multi_v7_defconfig kernel is run on the
> majority of platforms.
> I don't know whether any userspace has implemented any sort of
> workaround for this, but the ABI by itself is insufficient anyway.
> This series attempts to omit the spurious iWMMXt record when
> Not extensively tested, and the ABI impact is unknown for now.
Hmm, I would actually suggest that we poke in a correct size for the
missing iWMMXt record, and an invalid magic number as the "simple"
solution for this - that doesn't make any layout changes to the
data structures, and is probably the safest solution for backporting.
Going forward, I think something along the lines of your proposal is
RMK's Patch system: http://www.armlinux.org.uk/developer/patches/
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