Re: [PATCH v1 3/3] Documentation: x86-64: Document registers on entry and exit

[Ammar Faizi]

On 1/8/22 7:02 AM, Andy Lutomirski wrote:
> On 1/7/22 15:52, Ammar Faizi wrote:
> > There was a controversial discussion about the wording in the System
> > V ABI document regarding what registers the kernel is allowed to
> > clobber when the userspace executes syscall.
> >
> > The resolution of the discussion was reviewing the clobber list in
> > the glibc source. For a historical reason in the glibc source, the
> > kernel must restore all registers before returning to the userspace
> > (except for rax, rcx and r11).
[...]
> > diff --git a/Documentation/x86/entry_64.rst b/Documentation/x86/entry_64.rst
> > index e433e08f7018..3f2007e2a938 100644
> > --- a/Documentation/x86/entry_64.rst
> > +++ b/Documentation/x86/entry_64.rst
> > @@ -108,3 +108,50 @@ We try to only use IST entries and the paranoid entry code for vectors
> >   that absolutely need the more expensive check for the GS base - and we
> >   generate all 'normal' entry points with the regular (faster) paranoid=0
> >   variant.
> > +
> > +
> > +Registers on entry:
> > +-------------------
>
> This is SYSCALL64 registers on entry, not general registers on entry.
> Also, this has little to do with the entry logic, so it probably
> doesn't belong in this file.

Ah right, I should be more specific saying it's for syscall64 entry
as there are 6 entries mentioned in this document.

Should syscall64 entry topic be documented? If not I will drop it,
otherwise suggest me a place for it.

I think we can document it here, but it needs to be more specific
saying it's for syscall64 entry.

Jonathan?

--
Ammar Faizi

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