On Tue, Sep 15, 2020 at 05:50:54PM -0400, Arvind Sankar wrote:
> On Tue, Sep 15, 2020 at 10:49:12PM +0200, Borislav Petkov wrote:
> >
> > (Btw, clang doesn't need to add that "xor %eax,%eax" - panic() should not be
> > returning, ever. :-))
> >
>
> I think this is because panic() is varargs, and clang doesn't support
> gcc's -mskip-rax-setup. The normal ABI requires the caller to set RAX to
> the number of arguments in vector registers.
>
> https://patchwork.ozlabs.org/project/gcc/patch/20141218131150.ga32...@intel.com/
Ah, good point. Found this in the ABI doc:
"For calls that may call functions that use varargs or stdargs
(prototype-less calls or calls to functions containing ellipsis (...) in
the declaration) %al is used as hidden argument to specify the number of
vector registers used. The contents of %al do not need to match exactly
the number of registers, but must be an upper bound on the number of
vector registers used and is in the range 0–8 inclusive."
Thx.
--
Regards/Gruss,
Boris.
https://people.kernel.org/tglx/notes-about-netiquette
