Subject: Re: [PATCH v2 1/5] [ppc] Process dynamic relocations for kernel

From: Suzuki Poulose <[email-masked]>
Date: Wed, 09 Nov 2011 14:12:50 +0530

On 11/09/11 12:03, Suzuki Poulose wrote:
> On Tue, 08 Nov 2011 10:19:05 -0600
> Josh Poimboeuf<[email-masked]>  wrote:
>
>> On Tue, 2011-11-08 at 12:41 +0530, Suzuki Poulose wrote:
>>> What I was suggesting is, instead of flushing the cache in
>>> relocate(), lets do it like:
>>>
>>> for e.g, on 440x, (in head_44x.S :)
>>>
>>> #ifdef CONFIG_RELOCATABLE
>>> 	...
>>> 	bl relocate
>>>
>>> 	#Flush the d-cache and invalidate the i-cache here
>>> #endif
>>>
>>>
>>> This would let the different platforms do the the cache
>>> invalidation in their own way.
>>>
>>> Btw, I didn't find an instruction to flush the entire d-cache in
>>> PPC440 manual. We have instructions to flush only a block
>>> corresponding to an address.
>>>
>>> However, we have 'iccci' which would invalidate the entire i-cache
>>> which, which I think is better than 80,000 i-cache invalidates.
>>
>> In misc_32.S there are already some platform-independent cache
>> management functions.  If we use those, then relocate() could simply
>> call them.  Then the different platforms calling relocate() wouldn't
>> have to worry about flushing/invalidating caches.
>>
>> For example, there's a clean_dcache_range() function.  Given any range
>> twice the size of the d-cache, it should flush the entire d-cache.
>> But the only drawback is that it would require the caller to know the
>> size of the d-cache.
>>
>> Instead, I think it would be preferable to create a new clean_dcache()
>> (or clean_dcache_all()?) function in misc_32.S, which could call
>> clean_dcache_range() with the appropriate args for flushing the entire
>> d-cache.  relocate() could then call the platform-independent
>> clean_dcache().
>>
>
>
> How about using clean_dcache_range() to flush the range runtime
> address range [ _stext, _end ] ? That would flush the entire
> instructions.
>
>
>> For i-cache invalidation there's already the (incorrectly named?)
>> flush_instruction_cache().  It uses the appropriate platform-specific
>> methods (e.g. iccci for 44x) to invalidate the entire i-cache.
>
> Agreed. The only thing that worries me is the use of KERNELBASE in the
> flush_instruction_cache() for CONFIG_4xx. Can we safely assume all 4xx
> implementations ignore the arguments passed to iccci ?
>>
>> Suzuki, if you agree with this direction, I could work up a new patch
>> if needed.
>>
>
> I have the following (untested) patch which uses clean_dcache_range()
> and flush_instruction_cache(): I will send the next version soon
> with those changes and the DYNAMIC_MEMSTART config for oldstyle
> relocatoin, if every one agrees to this.
>
>
> diff --git a/arch/powerpc/kernel/reloc_32.S
> b/arch/powerpc/kernel/reloc_32.S index 045d61e..cce0510 100644
> --- a/arch/powerpc/kernel/reloc_32.S
> +++ b/arch/powerpc/kernel/reloc_32.S
> @@ -33,10 +33,9 @@ R_PPC_RELATIVE = 22
>
>   _GLOBAL(relocate)
>
> -	mflr	r0
> +	mflr	r14		/* Save our LR */
>   	bl	0f		/* Find our current runtime
> address */ 0:	mflr	r12		/* Make it
> accessible */
> -	mtlr	r0
>
>   	lwz	r11, (p_dyn - 0b)(r12)
>   	add	r11, r11, r12	/* runtime address of .dynamic
> section */ @@ -87,18 +86,19 @@ eodyn:				/*
> End of Dyn Table scan */
>   	 * Work out the current offset from the link time address
> of .rela
>   	 * section.
>   	 *  cur_offset[r7] = rela.run[r9] - rela.link [r7]
> -	 *  _stext.link[r10] = _stext.run[r10] - cur_offset[r7]
> -	 *  final_offset[r3] = _stext.final[r3] - _stext.link[r10]
> +	 *  _stext.link[r12] = _stext.run[r10] - cur_offset[r7]
> +	 *  final_offset[r3] = _stext.final[r3] - _stext.link[r12]
>   	 */
>   	subf	r7, r7, r9	/* cur_offset */
> -	subf	r10, r7, r10
> -	subf	r3, r10, r3	/* final_offset */
> +	subf	r12, r7, r10
> +	subf	r3, r12, r3	/* final_offset */
>
>   	subf	r8, r6, r8	/* relaz -= relaent */
>   	/*
>   	 * Scan through the .rela table and process each entry
>   	 * r9	- points to the current .rela table entry
>   	 * r13	- points to the symbol table
> +	 * r10  - holds the runtime address of _stext
>   	 */
>
>   	/*
> @@ -180,12 +180,23 @@ store_half:
>
>   nxtrela:
>   	cmpwi	r8, 0		/* relasz = 0 ? */
> -	ble	done
> +	ble	flush
>   	add	r9, r9, r6	/* move to next entry in
> the .rela table */ subf	r8, r6, r8	/* relasz -= relaent */
>   	b	applyrela
>
> -done:	blr
> +	/* Flush the d-cache'd instructions */
> +flush:
> +	mr	r3, r10
> +	lis	r4, (_end - _stext)@h
> +	ori	r4, r4, (_end - _stext)@l

Err ! This doesn't compile :

arch/powerpc/kernel/reloc_32.S: Assembler messages:
arch/powerpc/kernel/reloc_32.S:191: Error: can't resolve `_end' {*UND* section} - `_stext' {*UND* section}

I will fix it, but the idea remains the same.

Thanks

Suzuki