Re: [PATCH 1/5] x86: Add -mindirect-branch=

[David Woodhouse <dwmw2 at infradead dot org>]

On Mon, 2018-01-08 at 14:27 -0800, Andi Kleen wrote:
> On Mon, Jan 08, 2018 at 09:35:26PM +0000, David Woodhouse wrote:
> > On Mon, 2018-01-08 at 13:32 -0800, H.J. Lu wrote:
> > > On Mon, Jan 8, 2018 at 8:46 AM, Andi Kleen <ak@linux.intel.com> wrote:
> > > > 
> > > > "H.J. Lu" <hjl.tools@gmail.com> writes:
> > > > > 
> > > > > > 
> > > > > > 
> > > > > > Talking about PIC thunks, those have I believe . character in their symbols,
> > > > > > so that they can't be confused with user functions.  Any reason these
> > > > > > retpoline thunks aren't?
> > > > > > 
> > > > > They used to have '.'.  It was changed at the last minute since kernel needs to
> > > > > export them as regular symbols.
> > > > The kernel doesn't actually need that to export the symbols.
> > > > 
> > > > While symbol CRCs cannot be generated for symbols with '.', CRCs are not
> > > > needed and there were already patches to hide the resulting warnings.
> > > > 
> > > Andi, can you work it out with David?
> > 
> > It wasn't CONFIG_MODVERSIONS but CONFIG_TRIM_UNUSED_SYMBOLS which was
> > the straw that broke the camel's back on that one. I'm open to a
> > solution for that one, but I couldn't see one that didn't make my eyes
> > bleed. Except for making the symbols not have dots in.
> > 
> > https://patchwork.kernel.org/patch/10148081/
> 
> I guess we can stay with it the underscore version in the compiler now.
> 
> In theory it could conflict with something used in C, but the risk
> is probably low.

If it makes anyone happier, we could perhaps stick with the dot version
for the *inline* thunks but only use underscores for the external one?

But really, any "innocent user" claiming to be *surprised* after
writing their own C function and calling it __x86_indirect_thunk_rax is
surely taking the piss.

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