Stream: git-wasmtime

Topic: wasmtime / Issue #2856 Debug support for non-x86 architec...

Wasmtime GitHub notifications bot (Apr 21 2021 at 12:51):

uweigand opened Issue #2856:

Feature

Support debugging JITted WebAssembly code on non-x86 platforms.

Benefit

Currently, the debug crate only supports x86. All other platforms should be supported as well.

Implementation

There are a number of places that currently prevent the debug crate from supporting non-x86 platforms:

• Explicit architecture check in lib.rs:

    match header.e_machine.get(e) {
        EM_X86_64 => (),
        machine => {
            bail!("Unsupported ELF target machine: {:x}", machine);
        }
    }

(This should just go away, I think.)

• Explicit X86 assumptions in transform/expression.rs:

writer.write_op_breg(X86_64::RBP.0)?;
writer.write_sleb128(ss_offset as i64 + X86_64_STACK_OFFSET)?;

(This is only used for old-style back-ends and can probably go away soon.)

writer.write_op_breg(X86_64::RSP.0)?;

(This should probably use the register mapper that unwinder code also uses.)

• Various little-endian assumptions accessing ELF files and WebAssembly memory
  (See https://github.com/bytecodealliance/wasmtime/pull/2854 for details.)

• Additional endian issues (not solved by the PR above) in creating DWARF expressions
  Current code in transform/expression.rs simply copies portions of the incoming WebAssembly DWARF expressions directly into the native DWARF output. This is not correct in case the native architecture is big-endian. Fortunately, the byte code for many DWARF expressions is not endian-sensitive, so I can actually debug simple applications even so. But to be fully correct, those portions of DWARF bytecode that _are_ endian-sensitive will need to be handled here somehow.
  

Wasmtime GitHub notifications bot (Apr 21 2021 at 12:52):

uweigand commented on Issue #2856:

Hi @cfallin, this is the topic we talked about recently. I just wanted to open this issue to document all the places I've found where there is currently X86-specific code in the debug crate.

Last updated: Nov 22 2024 at 17:03 UTC