HI guys! I trying to implemnent wasm2wasm pass that remove specific
function from wasm. Inspired by ExtractFunction pass I wrote this
code:
for (auto& func : module->functions) {
if (names.find(func->name) != names.end()) {
// wipe out all the contents
std::cerr << "wipe out contents of " << func->name
<< std::endl;
func->vars.clear();
func->body = module->allocator.alloc<Unreachable>();
}
}
This works perfect, but when runtime tries to call this function it
throws exception with stack that does not contains removed function
name. So for example I removed 3650 functions from wasm binary, but
some function are actually used and I can't find name of excluded
function.
Typical output is:
RuntimeError: unreachable executed
<anonymous>
__GLOBAL__sub_I_ArrayMetadata_cpp
callRuntimeCallbacks
ensureInitRuntime
run
I think I can do what I want if I replace body of function with
abort() command, then I think exception will be:
RuntimeError: abort called
<REMOVED_FUNCTION_NAME>
__GLOBAL__sub_I_ArrayMetadata_cpp
callRuntimeCallbacks
ensureInitRuntime
run
So what I want to do is replace actual function code with:
{
abort();
}
Looking on other sources I think that following implemntation should work
for (auto& func : module->functions) {
if (names.find(func->name) != names.end()) {
// wipe out all the contents
std::cerr << "wipe out contents of " << func->name
<< std::endl;
func->vars.clear();
func->body = Builder(*module).makeCall("1", {},
none); // or unreachable
}
}
I use index "1" because "abort" is marked as 1 inside symbols file,
and also I checked with wasm2wat that 1 is abort:
(import "env" "abort" (func (;1;) (type 1)))
inside wat there are a lot of calls to 1, simle like this `call 1`
So, I think it should works, but when I run wasm-opt with this code I
always had error:
[wasm-validator error in function $3491] unexpected false: call param
number must match, on
[none] (call $1)
[wasm-validator error in function $3563] unexpected false: call param
number must match, on
[none] (call $1)
[wasm-validator error in function $3897] unexpected false: call param
number must match, on
[none] (call $1)
[wasm-validator error in function $3898] unexpected false: call param
number must match, on
[none] (call $1)
Also I tried just to preped function body with abort():
for (auto& func : module->functions) {
if (names.find(func->name) != names.end()) {
// wipe out all the contents
std::cerr << "wipe out contents of " << func->name
<< std::endl;
auto* abort = Builder(*module).makeCall("1", {}, none);
Builder builder(*module);
auto* block = builder.makeBlock();
block->list.push_back(abort);
block->list.push_back(func->body);
block->finalize(func->body->type);
func->body = block;
}
}
Output of wasm-opt absolutely same. Please help me to understand how
to call abort() function.
Thanks a lot!
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