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Re: arm: module: Add apply_relocate_add

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  Re: arm: module: Add apply_relocate_add Jessica Yu <jeyu@redhat.com> - 2017-01-17 05:50 +0100
    Re: arm: module: Add apply_relocate_add Miroslav Benes <mbenes@suse.cz> - 2017-01-18 11:40 +0100

#1560255 — Re: arm: module: Add apply_relocate_add

+++ Abel Vesa [06/12/16 17:06 +0000]:
>It was only added to fix compiler error. It is not implemented
>yet.
>
>Signed-off-by: Abel Vesa <abelvesa@linux.com>
>---
> arch/arm/kernel/module.c | 9 +++++++++
> 1 file changed, 9 insertions(+)
>
>diff --git a/arch/arm/kernel/module.c b/arch/arm/kernel/module.c
>index 4f14b5c..bf94922 100644
>--- a/arch/arm/kernel/module.c
>+++ b/arch/arm/kernel/module.c
>@@ -52,6 +52,15 @@ void *module_alloc(unsigned long size)
> #endif
>
> int
>+apply_relocate_add(Elf32_Shdr *sechdrs, const char *strtab,
>+		   unsigned int symindex, unsigned int relindex,
>+		   struct module *module)
>+{
>+	/* Not implemented yet */
>+	return 0;
>+}

Are SHT_RELA relocation sections actually supported on 32-bit arm? It looks
like there's only support for SHT_REL.

arch/arm/Kconfig:84:	select MODULES_USE_ELF_REL

If we support SHT_REL sections, the correct fix is to probably have
klp_write_object_relocations() check if the relocation section is
SHT_REL or SHT_RELA, and call the appropriate function (apply_relocate
or apply_relocate_add), similar to how the module loader does it.

Jessica

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#1561462

On Mon, 16 Jan 2017, Jessica Yu wrote:

> +++ Abel Vesa [06/12/16 17:06 +0000]:
> > It was only added to fix compiler error. It is not implemented
> > yet.
> > 
> > Signed-off-by: Abel Vesa <abelvesa@linux.com>
> > ---
> > arch/arm/kernel/module.c | 9 +++++++++
> > 1 file changed, 9 insertions(+)
> > 
> > diff --git a/arch/arm/kernel/module.c b/arch/arm/kernel/module.c
> > index 4f14b5c..bf94922 100644
> > --- a/arch/arm/kernel/module.c
> > +++ b/arch/arm/kernel/module.c
> > @@ -52,6 +52,15 @@ void *module_alloc(unsigned long size)
> > #endif
> > 
> > int
> > +apply_relocate_add(Elf32_Shdr *sechdrs, const char *strtab,
> > +		   unsigned int symindex, unsigned int relindex,
> > +		   struct module *module)
> > +{
> > +	/* Not implemented yet */
> > +	return 0;
> > +}
> 
> Are SHT_RELA relocation sections actually supported on 32-bit arm? It looks
> like there's only support for SHT_REL.
> 
> arch/arm/Kconfig:84:	select MODULES_USE_ELF_REL
> 
> If we support SHT_REL sections, the correct fix is to probably have
> klp_write_object_relocations() check if the relocation section is
> SHT_REL or SHT_RELA, and call the appropriate function (apply_relocate
> or apply_relocate_add), similar to how the module loader does it.

Agreed. According to arch/Kconfig and definitions you can use only one of 
MODULES_USE_ELF_REL and MODULES_USE_ELF_RELA. arm arch uses the former. So 
yes, I think we should use the same if/else construct from the module 
loader in klp_write_object_relocations()... and it should go with this 
patch set, because arm is the first arch to actually use SHT_REL and not 
SHT_RELA (iiuc). x86, s390 and powerpc (archs we support) use SHT_RELA.

Miroslav

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