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f0e421b1bf
Some kernel features don't currently work if a task puts a non-zero
address tag in its stack pointer, frame pointer, or frame record entries
(FP, LR).
For example, with a tagged stack pointer, the kernel can't deliver
signals to the process, and the task is killed instead. As another
example, with a tagged frame pointer or frame records, perf fails to
generate call graphs or resolve symbols.
For now, just document these limitations, instead of finding and fixing
everything that doesn't work, as it's not known if anyone needs to use
tags in these places anyway.
In addition, as requested by Dave Martin, generalize the limitations
into a general kernel address tag policy, and refactor
tagged-pointers.txt to include it.
Fixes: d50240a5f6ce ("arm64: mm: permit use of tagged pointers at EL0")
Cc: <stable@vger.kernel.org> # 3.12.x-
Reviewed-by: Dave Martin <Dave.Martin@arm.com>
Acked-by: Will Deacon <will.deacon@arm.com>
Signed-off-by: Kristina Martsenko <kristina.martsenko@arm.com>
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>
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.