[llvm-dev] [LLD] Adding WebAssembly support to lld

[Rafael Avila de Espindola via llvm-dev]

Sean Silva <chisophugis at gmail.com> writes:

> On Mon, Jul 3, 2017 at 11:12 AM, Rafael Avila de Espindola <
> rafael.espindola at gmail.com> wrote:
>
>> Sam Clegg via llvm-dev <llvm-dev at lists.llvm.org> writes:
>>
>> >> Can you elaborate on semantically what the linker is actually doing for
>> >> wasm?
>> >
>> > You are correct that the wasm linker does have more work to do than a
>> > traditional linker.  There are more sections that the linker will need
>> > to re-construct fully.  This is because there is more high level
>> > information required in the wasm format.  For example, as you point
>> > out, the type of each function.   Functions also live in their own
>> > index space outside of the program's memory space.  This means that
>> > the simple approach of traditional linkers where almost everything can
>> > be boiled down to virtual addresses don't make as much sense here.
>> > This is part of the reason why early attempts to use ELF as the
>> > encapsulation format were abandoned:  wasm is different enough that is
>> > didn't make sense.
>>
>> BTW, is that summarized somewhere?
>>
>> I remember the discussion about having relocations that would resolve to
>> function numbers, but I don't remember where that failed.
>>
>
> Looking at Sam's patch, it seems like that's what it does, e.g.
> R_WEBASSEMBLY_FUNCTION_INDEX_LEB

Sorry, I meant why that didn't work with ELF (or what else didn't).

Cheers,
Rafael