Re: [PATCH 02/22] ARM: use late patch framework for phys-virt patching

[Cyril Chemparathy]

Hi Nicolas,

On 8/4/2012 2:15 AM, Nicolas Pitre wrote:
> On Tue, 31 Jul 2012, Cyril Chemparathy wrote:
>
> > This patch replaces the original physical offset patching implementation
> > with one that uses the newly added patching framework.  In the process, we now
> > unconditionally initialize the __pv_phys_offset and __pv_offset globals in the
> > head.S code.
>
> Why unconditionally initializing those?  There is no reason for that.

We could keep this conditional on LPAE, but do you see any specific need 
for keeping it conditional?

> > Signed-off-by: Cyril Chemparathy <cyril@xxxxxx>
>
> Comments below.
>
> > diff --git a/arch/arm/kernel/head.S b/arch/arm/kernel/head.S
> > index 835898e..d165896 100644
> > --- a/arch/arm/kernel/head.S
> > +++ b/arch/arm/kernel/head.S
> [...]
> >   	.data
> >   	.globl	__pv_phys_offset
> >   	.type	__pv_phys_offset, %object
> >   __pv_phys_offset:
> >   	.long	0
> >   	.size	__pv_phys_offset, . - __pv_phys_offset
> > +
> > +	.globl	__pv_offset
> > +	.type	__pv_offset, %object
> >   __pv_offset:
> >   	.long	0
> > -#endif
> > +	.size	__pv_offset, . - __pv_offset
>
> Please move those to C code.  They aren't of much use in this file
> anymore.  This will allow you to use pphys_addr_t for them as well in
> your subsequent patch. And more importantly get rid of that ugly
> pv_offset_high that you introduced iin another patch.

Moving it to C-code caused problems because these get filled in prior to 
BSS being cleared.

We could potentially have this initialized in C with a mystery dummy 
value to prevent it from landing in BSS.  Would that be acceptable?

> > diff --git a/arch/arm/kernel/module.c b/arch/arm/kernel/module.c
> > index df5e897..39f8fce 100644
> > --- a/arch/arm/kernel/module.c
> > +++ b/arch/arm/kernel/module.c
> > @@ -317,11 +317,6 @@ int module_finalize(const Elf32_Ehdr *hdr, const Elf_Shdr *sechdrs,
> >   					         maps[i].txt_sec->sh_addr,
> >   					         maps[i].txt_sec->sh_size);
> >   #endif
> > -#ifdef CONFIG_ARM_PATCH_PHYS_VIRT
> > -	s = find_mod_section(hdr, sechdrs, ".pv_table");
> > -	if (s)
> > -		fixup_pv_table((void *)s->sh_addr, s->sh_size);
> > -#endif
> >   	s = find_mod_section(hdr, sechdrs, ".patch.table");
> >   	if (s)
> >   		patch_kernel((void *)s->sh_addr, s->sh_size);
>
> The patch_kernel code and its invokation should still be conditional on
> CONFIG_ARM_PATCH_PHYS_VIRT.  This ability may still be configured out
> irrespective of the implementation used.

Maybe CONFIG_ARM_PATCH_PHYS_VIRT is not quite appropriate if this is 
used to patch up other things in addition to phys-virt stuff?

I could have this dependent on CONFIG_ARM_INIT_PATCH (or whatever 
nomenclature we chose for this) and have CONFIG_ARM_PATCH_PHYS_VIRT 
depend on it.

> > diff --git a/arch/arm/kernel/vmlinux.lds.S b/arch/arm/kernel/vmlinux.lds.S
> > index bacb275..13731e3 100644
> > --- a/arch/arm/kernel/vmlinux.lds.S
> > +++ b/arch/arm/kernel/vmlinux.lds.S
> > @@ -162,11 +162,6 @@ SECTIONS
> >   		__smpalt_end = .;
> >   	}
> >   #endif
> > -	.init.pv_table : {
> > -		__pv_table_begin = .;
> > -		*(.pv_table)
> > -		__pv_table_end = .;
> > -	}
> >   	.init.patch_table : {
> >   		__patch_table_begin = .;
> >   		*(.patch.table)
>
> Since you're changing the module ABI,it is important to also modify the
> module vermagic string in asm/module.h to prevent the loading of
> incompatible kernel modules.

Absolutely.  Thanks.

> Nicolas

--
Thanks
- Cyril
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