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PING^2 [PATCH] x86: Add -mzero-caller-saved-regs=[skip|used-gpr|all-gpr|used|all]


On Thu, Nov 29, 2018 at 3:14 PM H.J. Lu <hjl.tools@gmail.com> wrote:
>
> On Wed, Oct 31, 2018 at 12:42 PM H.J. Lu <hjl.tools@gmail.com> wrote:
> >
> > On Thu, Sep 27, 2018 at 7:58 AM Richard Biener
> > <richard.guenther@gmail.com> wrote:
> > >
> > > On Thu, Sep 27, 2018 at 3:16 PM H.J. Lu <hjl.tools@gmail.com> wrote:
> > > >
> > > > On Thu, Sep 27, 2018 at 6:08 AM, Szabolcs Nagy <szabolcs.nagy@arm.com> wrote:
> > > > > On 26/09/18 19:10, H.J. Lu wrote:
> > > > >>
> > > > >> Add -mzero-caller-saved-regs=[skip|used|all] command-line option and
> > > > >> zero_caller_saved_regs("skip|used|all") function attribue:
> > > > >>
> > > > >> 1. -mzero-caller-saved-regs=skip and zero_caller_saved_regs("skip")
> > > > >>
> > > > >> Don't zero caller-saved integer registers upon function return.
> > > > >>
> > > > >> 2. -mzero-caller-saved-regs=used and zero_caller_saved_regs("used")
> > > > >>
> > > > >> Zero used caller-saved integer registers upon function return.
> > > > >>
> > > > >> 3. -mzero-caller-saved-regs=all and zero_caller_saved_regs("all")
> > > > >>
> > > > >> Zero all caller-saved integer registers upon function return.
> > > > >>
> > > > >> Tested on i686 and x86-64 with bootstrapping GCC trunk and
> > > > >> -mzero-caller-saved-regs=used as well as -mzero-caller-saved-regs=all
> > > > >> enabled by default.
> > > > >>
> > > > >
> > > > > from this description and the documentation it's
> > > > > not clear to me what this tries to achieve.
> > > > >
> > > > > is it trying to prevent information leak?
> > > > > or some pcs hack the caller may rely on?
> > > > >
> > > > > if it's for information leak then i'd expect such
> > > > > attribute to be used on crypto code.. however i'd
> > > > > expect crypto code to use simd registers as well,
> > > > > so integer only cleaning needs explanation.
> > > >
> > > > The target usage is in Linux kernel.
> > >
> > > Maybe still somehow encode that in the option since it otherwise raises
> > > expectations that are not met?
> > > -mzero-call-clobbered-regs=used-int|all-int|skip|used-simd|used-fp,etc.?
> > > and sorry() on unimplemented ones?  Or simply zero also non-integer
> > > regs the same way?  I suppose
> > > there isn't sth like vzeroupper that zeros all SIMD regs and completely?
> > >
> >
> > Here is the updated patch to zero caller-saved vector registers.   I don't
> > mind a different option name if it is preferred.  I may be able to create
> > some generic utility functions which can be used by other backends.  But
> > actual implementation must be target specific.
> >
> > Any comments?
>
> PING.
>
> https://gcc.gnu.org/ml/gcc-patches/2018-10/msg02079.html
>

PING.

-- 
H.J.


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