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

[Suzuki Poulose]

On Tue, 08 Nov 2011 10:19:05 -0600
Josh Poimboeuf <jpoimboe at linux.vnet.ibm.com> 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
+	add	r4, r3, r4
+	bl	clean_dcache_range
+	/* Invalidate the i-cache */
+	bl	flush_instruction_cache
+done:
+	mtlr	r14
+	blr
 
 
 p_dyn:		.long	__dynamic_start - 0b


Thanks

Suzuki