[PATCH 30/78] ARM: aarch64: Add relocation support

[Andrey Smirnov]

On Mon, Mar 19, 2018 at 1:50 AM, Sascha Hauer <s.hauer at pengutronix.de> wrote:
> Hi Andrey,
>
> On Fri, Mar 16, 2018 at 02:51:19PM -0700, Andrey Smirnov wrote:
>> On Fri, Mar 16, 2018 at 5:53 AM, Sascha Hauer <s.hauer at pengutronix.de> wrote:
>> > This adds aarch64 support for relocating binaries linked with -pie.
>> >
>> > Support is integrated into the already exisiting
>> > relocate_to_current_adr() function which is now used for both arm32
>> > and aarch64.
>> >
>> > Signed-off-by: Sascha Hauer <s.hauer at pengutronix.de>
>>
>>
>> Sascha:
>>
>> Two small suggestions w.r.t. this patch:
>>
>>  - I'd consider changing the code of relocate_to_current_adr() such
>> that AARCH64 specific codepaths are not taken on ARM32 (via IS_ENABLED
>> check or something similar)
>
> Why? Do you want to make the code more clear or do you fear that we
> apply fixups for a foreign architecture?
>

You'd be able to get the value of *_R_TYPE(type) once and then use
switch to structure code handling various types, which might be a bit
more readable. But that 50% personal preference, so feel free to keep
the code as is.

>>
>>  - I've always wanted to fix the original code to use Elf32_rel type
>> instead of magic hard-coded offsets, so depending on your
>> willingness/time-budget, maybe now would be a good time to do that as
>> well as use Elf64_rela for AARCH64?
>
> You mean using
>
>> struct elf32_rel {
>>       Elf32_Addr    r_offset;
>>       Elf32_Word    r_info;
>> } Elf32_Rel;
>
> and:
>
>> struct elf64_rela {
>>       Elf64_Addr r_offset;  /* Location at which to apply the action */
>>       Elf64_Xword r_info;   /* index and type of relocation */
>>       Elf64_Sxword r_addend;        /* Constant addend used to compute value */
>> } Elf64_Rela;
>
> ?

Yep, those are the two types.

>
> Yes, I can change that. I wonder though which type is behind R_ARM_ABS32
>

I think its still would be Elf32_Rel. From what I can tell both
R_ARM_ABS32 and R_ARM_RELATIVE calculate "*fixup = *fixup + offset"
using same pointer offsets it's just former also adds "r" that is
derived from "r_info". With enough #ifdefing it might even be possible
to convert that while() to a for() loop.

Thanks,
Andrey Smirnov