linux-kernel - Re: [PATCH 2/3] powerpc/module32: Use symbolic instructions names.

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Date:   Thu, 2 May 2019 09:24:37 +0200
From:   Christophe Leroy <christophe.leroy@....fr>
To:     Segher Boessenkool <segher@...nel.crashing.org>
Cc:     Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Paul Mackerras <paulus@...ba.org>,
        Michael Ellerman <mpe@...erman.id.au>,
        linuxppc-dev@...ts.ozlabs.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/3] powerpc/module32: Use symbolic instructions names.



Le 29/04/2019 à 13:54, Segher Boessenkool a écrit :
> On Mon, Apr 29, 2019 at 10:43:27AM +0000, Christophe Leroy wrote:
>> To increase readability/maintainability, replace hard coded
>> instructions values by symbolic names.
> 
>> +	/* lis r12,sym@ha */
>> +#define ENTRY_JMP0(sym)	(PPC_INST_ADDIS | __PPC_RT(R12) | PPC_HA(sym))
>> +	/* addi r12,r12,sym@l */
>> +#define ENTRY_JMP1(sym)	(PPC_INST_ADDI | __PPC_RT(R12) | __PPC_RA(R12) | PPC_LO(sym))
> 
> Those aren't "jump" instructions though, as the name suggests...  And you
> only have names for the first two of the four insns.  ("2" and "3" were
> still available ;-) )

Well, the idea was to say they are defining the jump destination.
Anyway, as they are used only once, let's put it directly in.

> 
>> -	entry->jump[0] = 0x3d800000+((val+0x8000)>>16); /* lis r12,sym@ha */
>> -	entry->jump[1] = 0x398c0000 + (val&0xffff);     /* addi r12,r12,sym@l*/
>> -	entry->jump[2] = 0x7d8903a6;                    /* mtctr r12 */
>> -	entry->jump[3] = 0x4e800420;			/* bctr */
>> +	entry->jump[0] = ENTRY_JMP0(val);
>> +	entry->jump[1] = ENTRY_JMP1(val);
>> +	entry->jump[2] = PPC_INST_MTCTR | __PPC_RS(R12);
>> +	entry->jump[3] = PPC_INST_BCTR;
> 
> Deleting the comment here is not an improvement imo.

Ok, I'll leave them in as I did for module64

Christophe

> 
> 
> Segher
>