Re: [PATCH v5 02/10] x86: Compile-time asm code validation

Josh Poimboeuf
2015-06-11T14:10:06Z

On Thu, Jun 11, 2015 at 08:10:50AM +0200, Ingo Molnar wrote:
> * Josh Poimboeuf <jpoimboe@redhat.com> wrote:
> > > I imagine that an automatic CFI annotation adder would walk through functions
> > > one instruction at a time and keep track of the frame state. If so, then it
> > > could verify that common jump targets had identical state and continue walking
> > > through them and annotating. I think this would get this case right, and it
> > > might be necessary anyway to handle jumps within functions.
> >
> > This would definitely add complexity to both asmvalidate and the CFI generator.
> > In fact it sounds like it would push the CFI generator out of its current awk
> > script territory and more into complex C code territory.
>
> I'd count that as a plus: awk isn't a common skillset while C is, and properly
> written it doesn't have to be _that_ complex.

The thing is, C is quite painful for text processing. And I think we'd
have to do the analysis at the source text level in order to generate
the .cfi_* instructions to pass to the gnu assembler.

C would definitely make more sense when analyzing object code. In fact,
asmvalidate is written in C. But then I guess we'd have to re-implement
the .cfi stuff and populate the DWARF sections manually instead of
letting the assembler do it.

--
Josh