Re: [RFC v4 07/18] objtool: Introduce INSN_UNKNOWN type

[Julien]

Hi Josh,

On 22/08/19 21:04, Josh Poimboeuf wrote:
> On Fri, Aug 16, 2019 at 01:23:52PM +0100, Raphael Gault wrote:
> > On arm64 some object files contain data stored in the .text section.
> > This data is interpreted by objtool as instruction but can't be
> > identified as a valid one. In order to keep analysing those files we
> > introduce INSN_UNKNOWN type. The "unknown instruction" warning will thus
> > only be raised if such instructions are uncountered while validating an
> > execution branch.
> >
> > This change doesn't impact the x86 decoding logic since 0 is still used
> > as a way to specify an unknown type, raising the "unknown instruction"
> > warning during the decoding phase still.
> >
> > Signed-off-by: Raphael Gault <raphael.gault@xxxxxxx>
>
> Is there a reason such data can't be moved to .rodata?  That would seem
> like the proper fix.

RaphaÃl can confirm, if I remember correctly, that issue was encountered 
on assembly files implementing crypto algorithms were some 
words/double-words of data were in the middle of the .text. I think it 
is done this way to make sure the data can be loaded in a single 
instruction. So moving it to another section could impact the crypto 
performance depending on the relocations.

That was my understanding at least.

Cheers,

--
Julien Thierry