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Subject: Re: [PATCH v8 23/30] powerpc: Add prefixed instructions to
 instruction data type
To: Alistair Popple <alistair@popple.id.au>
References: <20200506034050.24806-1-jniethe5@gmail.com>
 <20200506034050.24806-24-jniethe5@gmail.com>
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 <1850220.JuIOMCfrUL@townsend>
From: Christophe Leroy <christophe.leroy@csgroup.eu>
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Date: Thu, 14 May 2020 14:57:50 +0200
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Le 14/05/2020 à 14:06, Alistair Popple a écrit :
> On Thursday, 14 May 2020 4:11:43 PM AEST Christophe Leroy wrote:
>> @@ -249,7 +249,7 @@ int arch_prepare_optimized_kprobe(struct
>> optimized_kprobe *op, struct kprobe *p)
>>> * Fixup the template with instructions to:
>>> * 1. load the address of the actual probepoint
>>> */
>>> -       patch_imm64_load_insns((unsigned long)op, buff + TMPL_OP_IDX);
>>> +       patch_imm64_load_insns((unsigned long)op, 3, buff + TMPL_OP_IDX);
>>>
>>> /*
>>> * 2. branch to optimized_callback() and emulate_step()
>>> @@ -282,7 +282,11 @@ int arch_prepare_optimized_kprobe(struct
>>> optimized_kprobe *op, struct kprobe *p) /*
>>> * 3. load instruction to be emulated into relevant register, and
>>> */
>>> -       patch_imm32_load_insns(*p->ainsn.insn, buff + TMPL_INSN_IDX);
>>> +       temp = ppc_inst_read((struct ppc_inst *)p->ainsn.insn);
>>> +       patch_imm64_load_insns(ppc_inst_val(temp) |
>>> +                              ((u64)ppc_inst_suffix(temp) << 32),
>>> +                              4,
>>
>> So now we are also using r4 ? Any explanation somewhere on the way it
>> works ? This change seems unrelated to this patch, nothing in the
>> description about it. Can we suddenly use a new register without problem ?
> 
> Unless I missed something there is no change in register usage here that I
> could see. patch_imm32_load_insns() was/is hardcoded to use register r4.
> 

Ah ... Euh ... Ok I missed the change from patch_imm32_load_insns() to 
patch_imm64_load_insns(), I'll check again.