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There is a selftest that checks if FPRs are corrupted across a fork, aka clone. It was added as part of the series that optimised the clone path to save the parent's FP state without "giving up" (turning off FP). See commit8792468da5("powerpc: Add the ability to save FPU without giving it up"). The test encodes the assumption that FPRs 0-13 are volatile across the syscall, by only checking the volatile FPRs are not changed by the fork. There was also a comment in the fpu_preempt test alluding to that: The check_fpu function in asm only checks the non volatile registers as it is reused from the syscall test It is true that the function call ABI treats f0-f13 as volatile, however the syscall ABI has since been documented as *not* treating those registers as volatile. See commit7b8845a2a2("powerpc/64: Document the syscall ABI"). So change the test to check all FPRs are not corrupted by the syscall. Note that this currently fails, because save_fpu() etc. do not restore f0/vsr0. Signed-off-by: Michael Ellerman <mpe@ellerman.id.au> Link: https://msgid.link/20231128132748.1990179-5-mpe@ellerman.id.au
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.