On Wed, Mar 08, 2023 at 04:42:10PM +0100, Juergen Gross wrote:
> All functions referenced via __PV_IS_CALLEE_SAVE() need to be assembler
> functions, as those functions calls are hidden from gcc. 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.
>
> Signed-off-by: Juergen Gross <jgross@xxxxxxxx>
> ---
> arch/x86/include/asm/paravirt_types.h | 8 +++++++-
> arch/x86/kernel/paravirt.c | 27 ++++++---------------------
> 2 files changed, 13 insertions(+), 22 deletions(-)
Right, works with my particular reproducer.
Turning them into asm prevents the compiler from doing the
callee-clobbered zeroing and that's fine as this whole paravirt gunk is
hiding the "CALL" insn from it and you putting them in asm is in line
with this.
And a negative diffstat..
So yeah, I'll queue it soon unless someone objects.
Long term, I think we should continue switching all that pv stuff to
using the alternatives.
Thx.
--
Regards/Gruss,
Boris.
https://people.kernel.org/tglx/notes-about-netiquette
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