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Fix late-binding symbols with JSPI (implementation 2) #24161

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Fix late-binding symbols with JSPI (implementation 2) #24161

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0baf855
Fix late-binding symbols with JSPI (implementation 2)
hoodmane Apr 21, 2025
d787a87
Update test expectations
hoodmane Apr 21, 2025
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14 changes: 14 additions & 0 deletions src/lib/libdylink.js
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Original file line number Diff line number Diff line change
Expand Up @@ -685,6 +685,9 @@ var LibraryDylink = {
if (!resolved) {
resolved = moduleExports[sym];
}
if (resolved.orig) {
resolved = resolved.orig;
}
#if ASSERTIONS
assert(resolved, `undefined symbol '${sym}'. perhaps a side module was not linked in? if this global was expected to arrive from a system library, try to build the MAIN_MODULE with EMCC_FORCE_STDLIBS=1 in the environment`);
#endif
Expand Down Expand Up @@ -734,10 +737,21 @@ var LibraryDylink = {
// when first called.
if (!(prop in stubs)) {
var resolved;
#if JSPI
var func = (...args) => {
resolved ||= resolveSymbol(prop);
try {
resolved = WebAssembly.promising(resolved);
} catch(e) {}
return resolved(...args);
}
stubs[prop] = new WebAssembly.Suspending(func);
#else
stubs[prop] = (...args) => {
resolved ||= resolveSymbol(prop);
return resolved(...args);
};
#endif
}
return stubs[prop];
}
Expand Down
46 changes: 39 additions & 7 deletions test/core/test_dlfcn_jspi.c
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Original file line number Diff line number Diff line change
Expand Up @@ -3,27 +3,59 @@
// University of Illinois/NCSA Open Source License. Both these licenses can be
// found in the LICENSE file.

#include <assert.h>
#include <emscripten.h>
#include <stdio.h>
#include <dlfcn.h>

EM_ASYNC_JS(int, test, (), {
EM_ASYNC_JS(int, test_suspending, (), {
console.log("sleeping");
await new Promise(res => setTimeout(res, 0));
console.log("slept");
return 77;
});

int test_wrapper() {
return test();
int test_suspending_wrapper() {
return test_suspending();
}

EM_JS(int, test_sync, (), {
console.log("sync");
return 77;
})

int test_sync_wrapper() {
return test_sync();
}


typedef int (*F)();
typedef int (*G)(F f);

void helper(F f) {
void* handle = dlopen("side_a.so", RTLD_NOW|RTLD_GLOBAL);
assert(handle != NULL);
G side_module_trampolinea = dlsym(handle, "side_module_trampoline_a");
assert(side_module_trampolinea != NULL);
int res = side_module_trampolinea(f);
printf("okay %d\n", res);
}


EMSCRIPTEN_KEEPALIVE void not_promising() {
helper(test_sync_wrapper);
}

EM_JS(void, js_trampoline, (), {
_not_promising();
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@kripken this part of the test would work in #23619 but doesn't work here. In particular, if we call into C from JS via an export that isn't in JSPI_EXPORTS then we fail when calling into the stub trampoline. In my "make the trampoline WebAssembly" version, it works fine.

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Interesting, thanks... sounds like the JSPI spec changed and I haven't followed that closely.

@brendandahl is there some workaround for this issue?

If not, it sounds like this approach would need to add all late-binding symbols to JSPI_EXPORTS..?

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I think what would be needed would be to add all C functions that might call late-binding symbols to JSPI_EXPORTS? In this case the problem is fixed by adding -sJSPI_EXPORTS=not_promising.

If we wanted to go this way, we should probably make all exports JSPI_EXPORTS.

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One thing we could do is make a selector function with body like:

try (result restype)
   local.get 0
   local.get 1
   call suspendingTrampoline
catch $SuspendError
   local.get 0
   local.get 1
   call nonsuspendingTrampoline
end

and then make both a suspending and nonsuspending version of the stub. But this still forces us to do most of the painful stuff in #23619 where we calculate the type and generate a dynamic wasm module.

})

int main() {
void* handle = dlopen("side.so", RTLD_NOW|RTLD_GLOBAL);
F side_module_trampoline = dlsym(handle, "side_module_trampoline");
int res = side_module_trampoline();
printf("done %d\n", res);
printf("Suspending test\n");
helper(test_suspending_wrapper);
printf("Non suspending test\n");
js_trampoline();
printf("done\n");
return 0;
}

12 changes: 10 additions & 2 deletions test/core/test_dlfcn_jspi.out
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Original file line number Diff line number Diff line change
@@ -1,4 +1,12 @@
side_module_trampoline
Suspending test
side_module_trampoline_a
side_module_trampoline_b
sleeping
slept
done 77
okay 77
Non suspending test
side_module_trampoline_a
side_module_trampoline_b
sync
okay 77
done
10 changes: 10 additions & 0 deletions test/core/test_dlfcn_jspi_side_a.c
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Original file line number Diff line number Diff line change
@@ -0,0 +1,10 @@
#include <stdio.h>

typedef int (*F)();

int side_module_trampoline_b(F f);

int side_module_trampoline_a(F f) {
printf("side_module_trampoline_a\n");
return side_module_trampoline_b(f);
}
8 changes: 8 additions & 0 deletions test/core/test_dlfcn_jspi_side_b.c
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Original file line number Diff line number Diff line change
@@ -0,0 +1,8 @@
#include <stdio.h>

typedef int (*F)();

int side_module_trampoline_b(F f) {
printf("side_module_trampoline_b\n");
return f();
}
2 changes: 1 addition & 1 deletion test/other/codesize/test_codesize_hello_dylink.gzsize
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@@ -1 +1 @@
11735
11736
2 changes: 1 addition & 1 deletion test/other/codesize/test_codesize_hello_dylink.jssize
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@@ -1 +1 @@
27774
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23 changes: 17 additions & 6 deletions test/test_core.py
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Original file line number Diff line number Diff line change
Expand Up @@ -3789,13 +3789,24 @@ def test_dlfcn_jspi(self):
self.run_process(
[
EMCC,
"-o",
"side.so",
test_file("core/test_dlfcn_jspi_side.c"),
"-sSIDE_MODULE",
] + self.get_emcc_args()
'-o',
'side_b.so',
test_file('core/test_dlfcn_jspi_side_b.c'),
'-sSIDE_MODULE',
]
+ self.get_emcc_args()
)
self.run_process(
[
EMCC,
'-o',
'side_a.so',
test_file('core/test_dlfcn_jspi_side_a.c'),
'-sSIDE_MODULE',
]
+ self.get_emcc_args()
)
self.do_run_in_out_file_test("core/test_dlfcn_jspi.c", emcc_args=["side.so", "-sMAIN_MODULE=2"])
self.do_run_in_out_file_test('core/test_dlfcn_jspi.c', emcc_args=['side_a.so', 'side_b.so', '-sMAIN_MODULE=2', '-g'])

@needs_dylink
def test_dlfcn_rtld_local(self):
Expand Down
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