[dylink] Fix rpath calculation in nested dependencies

[ryanking13]

This fixes a bug in rpath calculation in nested dependencies.

Basically, it fixes a case when a relative path is passed to the loadDynamicLibrary.

Think of the following scenario:

0. libhello.wasm depends on libhello_dep.so depends on libhello_nested_dep.so
1. [main.c] calls dlopen('/usr/lib/libhello.wasm')
2. [dynlink.c] calls loadDynamicLibrary('/usr/lib/libhello.wasm') (_dlopen_js ==> dlopenInternal ==> loadDynamicLibrary)
3. [libdylink.js] inside loadDynamicLibrary('/usr/lib/libhello.wasm'), it loads the dependency libhello_dep.so. When locating libhello_dep.so, it uses parentLibPath: /usr/lib/libhello.wasm it locates the library correctly from /usr/lib/libhello_dep.so.
4. [libdylink.js] Now we call loadDynamicLibrary('libhello_dep.so'), and it loads its dependency 'libhello_nested_dep.so' first. In this case it uses parentLibPath: libhello_dep.so so it fails to locate the library.

[ryanking13]

@sbc100, May I ask for your review again when you have time?

[sbc100]

@ryanking13 I'm curious about the different between this patch and #25694. Do they both solve the same issue? Do you have a preference for one over the other?

[sbc100]

Also, could you rebase (or merge) this ?

[ryanking13]

@ryanking13 I'm curious about the different between this patch and https://github.com/emscripten-core/emscripten/pull/25694. Do they both solve the same issue? Do you have a preference for one over the other?

@sbc100 Thanks for the review!

I think both approaches somehow solve this nested dependency issue, but I prefer mine because I think this is more straightforward. https://github.com/emscripten-core/emscripten/pull/25694 modifies the libName variable in multiple places which increases the cognitive load. This PR always resolves the libname before running loadDynamicLibrary soi I think it is better.

[ryanking13]

@sbc100

Would this also fix https://github.com/emscripten-core/emscripten/issues/25814?

Unfortunately no, I tested the worker case but I get fiile not found error. Does --embed-file parameter work differently in worker?

[sbc100]

To get the codesize expectations to match you need to run toosl/main/rebaseline_test.py after first doing emsdk install tot. If you have having trouble doing that let me know and I can push the expected results.

[ryanking13]

@sbc100

To get the codesize expectations to match you need to run toosl/main/rebaseline_test.py after first doing emsdk install tot. If you have having trouble doing that let me know and I can push the expected results.

Thanks, updated the codesize. I think where was some code courrupted in my cache.