WebAssembly / WebAssembly/wabt

Output results of the wasm-decompile to be easier to understand which function is called by call_indirect

Open
#2,384 1 comment 0 reactions 0 assignees View on GitHub

Nobody has claimed this yet.

Dominant language
C++
Stars
8.1k
Forks
827
Avg merge
4d 6h
Merged PRs (30d)
18

Description

The decompiled output from wasm-decompile can be challenging to interpret since the function table is omitted from the resulting files. Annotating the function index within the output aids in comprehending which function is being invoked by the call_indirect instruction.
Consider the following WebAssembly text file, a.wat:

(module
  (type $FUNCSIG$i (func (param i32) (result i32)))
  (table 0 1 funcref)
  (elem (i32.const 0) funcref (ref.func $test))
  (memory $0 1)

  (func $test (type $FUNCSIG$i) (param $p i32) (result i32)
    local.get $p
    i32.const 42
    i32.add
  )

  (func $main (result i32)
    i32.const 42
    i32.const 0
    call_indirect (type $FUNCSIG$i)
  )
)

After running the following commands:

wat2wasm a.wat -o a.wasm
wasm-decompile a.wasm -o a.dcmp

I obtained the decompiled output as such:

memory M_a(initial: 1, max: 0);

table T_a:funcref(min: 0, max: 1);

function f_a(a:int):int {
  return a + 42
}

function f_b():int {
  return call_indirect(42, 0)
}

This decompiled file lacks information about the function table. Moreover, the arguments of the call_indirect function are not immediately clear.
For clearer understanding, consider the decompiled output if it were presented in the following manner:

memory M_a(initial: 1, max: 0);

table T_a:funcref[f_a];

// funcref[0]
function f_a(a:int):int {
  return a + 42
}

function f_b():int {
  return call_indirect(funcref[0])(42)
}

With such modifications, it would be more apparent which function the call_indirect is calling.

Contributor guide

Open the contributing guide

First steps

  1. Read the whole issue, then the project's contributing guide.
  2. Comment on the issue to say you are picking it up — it saves two people doing the same work.
  3. Fork the repository and make your change on a branch.
  4. Open a pull request that references the issue number.

Research direction

Start by reproducing the issue with wat2wasm and wasm-decompile using the a.wat example in the report, then trace how wasm-decompile emits tables, functions, and call_indirect expressions. Done means the decompiled output preserves enough function-table information to identify the indirect target and makes the call_indirect arguments clear, as illustrated in the proposed output.

Written by the indexing model from the issue text.

Assessment

Tech stack
cpp, wasm
Domain
compilers
Issue type
Feature
Difficulty
4/5
Estimated time
3-5 days
Activity status
Stale
Clarity
Mostly clear
Newbie friendliness
38/100

Get new issues in your inbox

A short digest of beginner-friendly GitHub issues.