linux-kernel - Re: [PATCH v3 3/3] powerpc/module64: Use symbolic instructions names.

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Message-ID: <87wogneo07.fsf@concordia.ellerman.id.au>
Date:   Fri, 12 Jul 2019 17:00:08 +1000
From:   Michael Ellerman <mpe@...erman.id.au>
To:     Christophe Leroy <christophe.leroy@....fr>,
        Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Paul Mackerras <paulus@...ba.org>
Cc:     linux-kernel@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org,
        Ulirch Weigand <Ulrich.Weigand@...ibm.com>
Subject: Re: [PATCH v3 3/3] powerpc/module64: Use symbolic instructions names.

Christophe Leroy <christophe.leroy@....fr> writes:
> Le 08/07/2019 à 02:56, Michael Ellerman a écrit :
>> Christophe Leroy <christophe.leroy@....fr> writes:
>>> To increase readability/maintainability, replace hard coded
>>> instructions values by symbolic names.
>>>
>>> Signed-off-by: Christophe Leroy <christophe.leroy@....fr>
>>> ---
>>> v3: fixed warning by adding () in an 'if' around X | Y (unlike said in v2 history, this change was forgotten in v2)
>>> v2: rearranged comments
>>>
>>>   arch/powerpc/kernel/module_64.c | 53 +++++++++++++++++++++++++++--------------
>>>   1 file changed, 35 insertions(+), 18 deletions(-)
>>>
>>> diff --git a/arch/powerpc/kernel/module_64.c b/arch/powerpc/kernel/module_64.c
>>> index c2e1b06253b8..b33a5d5e2d35 100644
>>> --- a/arch/powerpc/kernel/module_64.c
>>> +++ b/arch/powerpc/kernel/module_64.c
>>> @@ -704,18 +711,21 @@ int apply_relocate_add(Elf64_Shdr *sechdrs,
>> ...
>>>   			/*
>>>   			 * If found, replace it with:
>>>   			 *	addis r2, r12, (.TOC.-func)@ha
>>>   			 *	addi r2, r12, (.TOC.-func)@l
>>>   			 */
>>> -			((uint32_t *)location)[0] = 0x3c4c0000 + PPC_HA(value);
>>> -			((uint32_t *)location)[1] = 0x38420000 + PPC_LO(value);
>>> +			((uint32_t *)location)[0] = PPC_INST_ADDIS | __PPC_RT(R2) |
>>> +						    __PPC_RA(R12) | PPC_HA(value);
>>> +			((uint32_t *)location)[1] = PPC_INST_ADDI | __PPC_RT(R2) |
>>> +						    __PPC_RA(R12) | PPC_LO(value);
>>>   			break;
>> 
>> This was crashing and it's amazing how long you can stare at a
>> disassembly and not see the difference between `r2` and `r12` :)
>
> Argh, yes. I was misleaded by the comment I guess. Sorry for that and 
> thanks for fixing.

No worries, yes the comment was the problem. I fixed that as well.

cheers