Oz and symbols

[Александр Гурьянов]

HI. I used wasm-opt manually to optimize wasm binary. On last step I
used Oz to finalize optimizations. My problem is that after Oz
function indexes is changed and I can't get symbols map to restore
function names. How I can map new function indexes to old one (from
symbols file).

In other words:
1) I have bin.wasm from emscripten with symbols file. E.g. for one function:
export __GLOBAL__sub_I_Runtime_BaseClasses_0_cpp (func $3425) - 3809

2) I do some buisness releated optimizations (with wasm-opt) that
didn't change function indexes, after this, I still have
export __GLOBAL__sub_I_Runtime_BaseClasses_0_cpp (func $3425) - 3809

3) Next I finalize build with wasm-opt -Oz, after it indexes was
changed (I think because of dead code elimination), and I have
export "__GLOBAL__sub_I_Runtime_BaseClasses_0_cpp" (func $1637) - 1997

I need some flag for Oz, that told generates mapping for new indexes,
like $1637: $3425 then I can restore original function names. I think
some flag or option to do it should be already there, because
emscripten do this in some way. What is the best way to build this
mappings?

[Alon Zakai]

In general the way to do this is to keep names around all the time until the very end. So run emcc with --profiling-funcs. Then when you run wasm-opt later, run it with -g. Then in your final wasm-opt command, do *not* use -g, and instead run --print-function-map which is what is used to print the function map by emcc.

Another way might be to use the BINARYEN_EXTRA_PASSES flag. Then emcc will run extra wasm-opt work for you internally.

- Alon

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