[LLVMdev] EHABI: Remaining issues

Logan Chien tzuhsiang.chien at gmail.com
Tue Mar 18 11:02:17 PDT 2014


Hi Renato,

Although replacing ARM-specific directives in favor of CFI directives is a
desirable movement, I think the compatibility should be considered
carefully before we stop to emit the ARM-specific directives.

Maybe a reasonable criteria is that there are at least two major releases
of GNU binutils assembler which can emit EHABI tables by reading CFI
directives?

Sincerely,
Logan


On Sun, Mar 16, 2014 at 2:47 AM, Renato Golin <renato.golin at linaro.org>wrote:

> On 15 March 2014 17:06, Logan Chien <tzuhsiang.chien at gmail.com> wrote:
> > I would like to know what do you mean by "commoning them up"?
>
> Hi Logan,
>
> That'd be reducing ARM directives in favour of CFI, but as I said (and
> you too), GNU compatibility will probably be an issue for a very long
> time.
>
>
> > For the space issue, I personally don't think this is a big issue.  For
> the
> > code without exception handling, only stack informations will be encoded.
> > Besides, the encoding format is very compact.  In the common cases, the
> code
> > without exception handling needs only 8-12 bytes per function.  If this
> is
> > still an issue, then -fno-unwind-table might be a solution (i.e. at llvm
> > assembly level, the function should be marked with nounwind and without
> > uwtable.)
>
> Yes, and that's what my merge request implements:
>
> http://llvm-reviews.chandlerc.com/D3079
>
> As soon as that's in, I believe EHABI is finally in good shape to be
> called Beta.
>
> Since the 3.4 release I'm trying to get the EHABI and IAS support in
> good shape (removing the final restraints, testing a lot), for them to
> be enabled by default in 3.5, and I think we got it, thanks to you,
> Anton, Saleem and many others.
>
> cheers,
> --renato
>
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