Subject: Re: [PATCH v2 16/16] objtool/powerpc: Add --mcount specific implementation

From: Segher Boessenkool <[email-masked]>
Date: Wed, 31 Aug 2022 12:51:00 -0500

On Wed, Aug 31, 2022 at 12:50:07PM +0000, Christophe Leroy wrote:
> Le 29/08/2022 à 07:52, Sathvika Vasireddy a écrit :
> > +	opcode = insn >> 26;
> > +
> > +	switch (opcode) {
> > +	case 18: /* bl */
> 
> case 18 is more than 'bl', it includes also 'b'.
> In both cases, the calculation of *immediate is the same.

It also is "ba" and "bla", sometimes written as "b[l][a]".

> It would therefore be more correct to perform the calculation and setup 
> of *immediate outside the 'if ((insn & 3) == 1)', that would avoid 
> unnecessary churn the day we add support for branches without link.
> 
> > +		if ((insn & 3) == 1) {
> > +			*type = INSN_CALL;
> > +			*immediate = insn & 0x3fffffc;
> > +			if (*immediate & 0x2000000)
> > +				*immediate -= 0x4000000;
> > +		}
> > +		break;
> > +	}

Does this handle AA=1 correctly at all?  That is valid both with and
without relocations, just like AA=0.  Same for AA=1 LK=0 btw.

If you only handle AA=0, the code should explicitly test for that.

Segher