linux-kernel - Re: [PATCH] powerpc/booke: Avoid link stack corruption in several places

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Date:   Mon, 23 Aug 2021 19:05:38 +0200
From:   Christophe Leroy <christophe.leroy@...roup.eu>
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] powerpc/booke: Avoid link stack corruption in several
 places



Le 23/08/2021 à 17:58, Segher Boessenkool a écrit :
> On Mon, Aug 23, 2021 at 07:53:01AM +0000, Christophe Leroy wrote:
>>   /* Be careful, this will clobber the lr register. */
>>   #define LOAD_REG_ADDR_PIC(reg, name)		\
>> -	bl	0f;				\
>> +	bcl	20,31,0f			\
>>   0:	mflr	reg;				\
>>   	addis	reg,reg,(name - 0b)@ha;		\
>>   	addi	reg,reg,(name - 0b)@l;
> 
> The code ended each line with a semicolon before, for absolutely no
> reason that I can see, but still.  Fixing that would be nice, but only
> doing it on one line isn't good.

Sure, forgetting the semicolon broke the build. That's because the backslash removes the newline.

The cleanest way I found to fix that quite of stuff is by using GAS macro, as I did for 
LOAD_REG_IMMEDIATE() some time ago.

> 
> Btw.  Both the 7450 and the modern cores implementing this really need
> this to be $+4, so it is a lot clearer to write that instead of 1f or
> a named label.

I like that, removing unneeded labels will make it smoother and clearer. I'll do it.

Christophe