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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> Signed-off-by: Russell King <rmk+kernel@armlinux.org.uk>
Linux kernel ============ This file was moved to Documentation/admin-guide/README.rst Please notice that there are several guides for kernel developers and users. These guides can be rendered in a number of formats, like HTML and PDF. In order to build the documentation, use ``make htmldocs`` or ``make pdfdocs``. There are various text files in the Documentation/ subdirectory, several of them using the Restructured Text markup notation. See Documentation/00-INDEX for a list of what is contained in each file. Please read the Documentation/process/changes.rst file, as it contains the requirements for building and running the kernel, and information about the problems which may result by upgrading your kernel.