* Denys Vlasenko <dvlas...@redhat.com> wrote:
> On 03/24/2015 07:34 AM, Ingo Molnar wrote:
> >
> > * Denys Vlasenko <vda.li...@googlemail.com> wrote:
> >
> >> On Mon, Mar 23, 2015 at 9:38 PM, Andy Lutomirski <l...@amacapital.net>
> >> wrote:
> >>> Actually, I want to remove the added comment in the code. I don't see
> >>> why we should have a specific comment about SS and not about, say, CS,
> >>> ESP, or anything else. OK?
> >>
> >> Ok.
> >
> > Might be nice to place a more generic description there, which
> > registers are expected to be saved by user-space calling in here, etc.
>
> __kernel_vsyscall entry point has the same ABI in any 32-bit vDSO,
> the good old int 0x80 calling convention:
>
> syscall# in eax,
> params in ebx/ecx/edx/esi/edi/ebp,
> all registers are preserved by the syscall.
>
> (I think we don't guarantee that all flags are preserved:
> I have a testcase where DF gets cleared).
I think the fact that the people developing this code are unsure about
exactly what gets saved/restored is justification enough to document
the circumstances a bit better.
> Each flavor of fast kernel call does necessary massaging to conform
> to the ABI. E.g. SYSCALL-based fast call clobbers ecx, so its vDSO
> saves/restores ecx on stack.
>
> Do you want a patch which adds such comment into every vDSO?
Well, maybe it's better to extend the already existing descriptions at
the syscall entry points to be a full description of all details, and
put a reference to that description into the vDSOs?
Thanks,
Ingo
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majord...@vger.kernel.org
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/
