[Uclinux-h8-devel] [PATCH] treewide: remove current_text_addr

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Nick Desaulniers ndesa****@googl*****
2018年 9月 1日 (土) 01:48:56 JST

On Mon, Aug 27, 2018 at 6:34 AM H. Peter Anvin <hpa****@zytor*****> wrote:
> On 08/27/18 06:11, Peter Zijlstra wrote:
> > On Mon, Aug 27, 2018 at 05:26:53AM -0700, H. Peter Anvin wrote:
> >
> >> _THIS_IP_, however, is completely ill-defined, other than being an
> >> address *somewhere* in the same global function (not even necessarily
> >> the same function if the function is static!)  As my experiment show, in
> >> many (nearly) cases gcc will hoist the address all the way to the top of
> >> the function, at least for the current generic implementation.
> >
> > It seems to have mostly worked so far... did anything change?
> >
> Most likely because the major architectures contain a arch-specific
> assembly implementation.  The generic implementation used in some places
> is completely broken, as my experiments show.
> >> For the case where _THIS_IP_ is passed to an out-of-line function in all
> >> cases, it is extra pointless because all it does is increase the
> >> footprint of every caller: _RET_IP_ is inherently passed to the function
> >> anyway, and with tailcall protection it will uniquely identify a callsite.
> >
> > So I think we can convert many of the lockdep _THIS_IP_ calls to
> > _RET_IP_ on the other side, with a wee bit of care.
> >
> > A little something like so perhaps...
> I don't have time to look at this right now (I'm on sabbatical, and I'm
> dealing with personal legal stuff right at the moment), but I think it
> is the right direction.
>         -hpa

Can this patch please be merged?  Then we can polish off Peter's
change to lockdep to not even use _THIS_IP_.

~Nick Desaulniers

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