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All functions referenced via __PV_IS_CALLEE_SAVE() need to be assembler functions, as those functions calls are hidden from the compiler. In case the kernel is compiled with "-fzero-call-used-regs" the compiler will clobber caller-saved registers at the end of C functions, which will result in unexpectedly zeroed registers at the call site of the related paravirt functions. Replace the C functions with DEFINE_PARAVIRT_ASM() constructs using the same instructions as the related paravirt calls in the PVOP_ALT_[V]CALLEE*() macros. And since they're not C functions visible to the compiler anymore, latter won't do the callee-clobbered zeroing invoked by -fzero-call-used-regs and thus won't corrupt registers. [ bp: Extend commit message. ] Signed-off-by: Juergen Gross <jgross@suse.com> Signed-off-by: Borislav Petkov (AMD) <bp@alien8.de> Link: https://lore.kernel.org/r/20230317063325.361-1-jgross@suse.com
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.