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Re: [RFC PATCH v2 2/2] ARM: signal: Fix unparseable iwmmxt_sigframe in uc_regspace
- 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: Tue, 27 Jun 2017 23:08:12 +0100
- Subject: Re: [RFC PATCH v2 2/2] ARM: signal: Fix unparseable iwmmxt_sigframe in uc_regspace
- Authentication-results: sourceware.org; auth=none
- References: <1498583067-14178-1-git-send-email-Dave.Martin@arm.com> <1498583067-14178-3-git-send-email-Dave.Martin@arm.com>
On Tue, Jun 27, 2017 at 06:04:07PM +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.
> The cause is that the uc_regspace is laid out statically based on
> the kernel config, but the decision of whether to save/restore the
> iWMMXt registers must be a runtime decision.
> To minimise breakage of software that may assume a fixed layout,
> this patch emits a dummy block of the same size as iwmmxt_sigframe,
> for non-iWMMXt threads. However, the magic and size of this block
> are now filled in to help parsers skip over it. A new DUMMY_MAGIC
> is defined for this purpose.
> It is probably legitimate (if non-portable) for userspace to
> manufacture its own sigframe for sigreturn, and there is no obvious
> reason why userspace should be required to insert a DUMMY_MAGIC
> block when running on non-iWMMXt hardware, when omitting it has
> worked just fine forever in other configurations. So in this case,
> sigreturn does not require this block to be present.
> Reported-by: Edmund Grimley-Evans <Edmund.Grimley-Evans@arm.com>
> Signed-off-by: Dave Martin <Dave.Martin@arm.com>
This looks fine to me. Please drop it in the patch system, thanks.
RMK's Patch system: http://www.armlinux.org.uk/developer/patches/
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