[PATCH] Allow ARM ELF relocs to be applied twice

[Tim Northover]

Ping?

On Sat, May 25, 2013 at 9:16 AM, Tim Northover <t.p.northover at gmail.com> wrote:
> Hi,
>
> This patch is designed to fix PR16013, which notes that ARM's MCJIT
> relocation processing can't be reliably applied twice since each
> iteration changes the state used by the next. It should allow remote
> MCJIT to work reliably on ARM ELF.
>
> The bulk of the patch brings ARM in line with other targets (like
> i386) in taking the .rel addends from the object-file as emitted
> rather than the one being modified.
>
> However, there is an extra complication which I think deserves review.
> The stubs created by the JIT need relocation, but don't actually have
> any addend bits to take from the emitted object-file. This means that
> none of the generic handling can work for them.
>
> There are two potential solutions to this:
> 1. Use the R_ARM_PRIVATE_0 special relocation completely internally
> within RuntimeDyldELF (see patch).
> 2. Teach generic RuntimeDyld about the difference between .rel and
> .rela relocations, so that it can handle object files emitted using
> both styles. Then the stubs would become a .rela style R_ARM_ABS32
> with addend 0.
>
> I decided that the second option was rather heavyweight since I can't
> see LLVM ever actually emitting both .rel and .rela sections.
>
> OK to commit?
>
> Tim.
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