Re: [PATCH v1 1/6] objtool/powerpc: Add build-time fixup of alternate feature branch targets

["Christophe Leroy (CS GROUP)" <chleroy@kernel.org>]

Le 05/05/2026 à 16:49, Peter Zijlstra a écrit :
> On Tue, May 05, 2026 at 04:45:39PM +0200, Peter Zijlstra wrote:
>> On Tue, May 05, 2026 at 02:16:23PM +0530, Sathvika Vasireddy wrote:
>>>   	switch (opcode) {
>>> +	case 16:
>>
>> Like case 18 below, this wants a comment describing which instruction
>> this is; bclr ?

No, it is bc/bca/bcl/bcla, it is quite similar to type 18 which is 
b/ba/bl/bla, but that's a conditional branch to a 14-bit offset while 
type 18 is a non-conditional branch to a 24-bit offset (10 bits are the 
conditional in the bc, hence the reduced offset size).


> 
> Also, isn't that typically used for return, suggesting at least
> something should have INSN_RETURN on?
> 

bclr (which is the return INSN_RETURN) has type 19

By the way you can have a look at 
https://patchwork.ozlabs.org/project/linuxppc-dev/patch/bfa8364da047d8610a09458a1cd924a0566aedbb.1736955567.git.christophe.leroy@csgroup.eu/

That patch has all the objtool decoding. By the way objtool is missing a 
INSN_CONDITIONAL_RETURN, also see 
https://patchwork.ozlabs.org/project/linuxppc-dev/patch/537e5d8f181b1f1c2b8918f1aefa1dba3f972c03.1736955567.git.christophe.leroy@csgroup.eu/



>>> +		if (ins & 1)
>>> +			typ = INSN_OTHER;
>>> +		else
>>> +			typ = INSN_JUMP_CONDITIONAL;
>>> +		imm = ins & 0xfffc;
>>> +		if (imm & 0x8000)
>>> +			imm -= 0x10000;
>>> +		insn->immediate = imm | aa;
>>> +		break;
>>> +
>>>   	case 18: /* b[l][a] */
>>>   		if (ins == 0x48000005)	/* bl .+4 */
>>>   			typ = INSN_OTHER;