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Mark Rutland
9df3f5082f
In old versions of GCC and Clang, __builtin_return_address() did not
strip the PAC. This was not the behaviour we desired, and so we wrapped
this with code to strip the PAC in commit:
689eae42af ("arm64: mask PAC bits of __builtin_return_address")
Since then, both GCC and Clang decided that __builtin_return_address()
*should* strip the PAC, and the existing behaviour was a bug.
GCC was fixed in 11.1.0, with those fixes backported to 10.2.0, 9.4.0,
8.5.0, but not earlier:
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=94891
Clang was fixed in 12.0.0, though this was not backported:
https://reviews.llvm.org/D75044
When using a compiler whose __builtin_return_address() strips the PAC,
our wrapper to strip the PAC is redundant. Similarly, when pointer
authentication is not in use within the kernel pointers will not have a
PAC, and so there's no point stripping those pointers.
To avoid this redundant work, this patch updates the
__builtin_return_address() wrapper to only be used when in-kernel
pointer authentication is configured and the compiler's
__builtin_return_address() does not strip the PAC.
This is a cleanup/optimization, and not a fix that requires backporting.
Stripping a PAC should be an idempotent operation, and so redundantly
stripping the PAC is not harmful.
There should be no functional change as a result of this patch.
Signed-off-by: Mark Rutland <[email protected]>
Cc: Amit Daniel Kachhap <[email protected]>
Cc: Catalin Marinas <[email protected]>
Cc: James Morse <[email protected]>
Cc: Kristina Martsenko <[email protected]>
Cc: Will Deacon <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Will Deacon <[email protected]>
Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.
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.