wasm and wasm-unknown: allocator always allocates 2 pages (2x64k) about tinygo HOT 7 OPEN

@deadprogram asked me for a smaller code to reproduce and without Rust.

main.go:

package main

var data []byte

//go:export boot
func Boot() {
	fileSize := 1
	data = make([]byte, fileSize)
	data[0] = 3
	f(data)
}

//go:noinline
func f([]byte) {}

target.json:

{
  "llvm-target": "wasm32-unknown-unknown",
  "cpu": "generic",
  "features": "+mutable-globals,+nontrapping-fptoint,+sign-ext,+bulk-memory",
  "build-tags": ["tinygo.wasm", "wasm_unknown"],
  "goos": "linux",
  "goarch": "arm",
  "linker": "wasm-ld",
  "rtlib": "compiler-rt",
  "scheduler": "none",
  "gc": "leaking",
  "libc": "wasmbuiltins",
  "cflags": ["-mno-bulk-memory", "-mnontrapping-fptoint", "-msign-ext"],
  "ldflags": [
    "--allow-undefined",
    "--no-demangle",
    "--initial-memory=65536",
    "--max-memory=65536",
    "--stack-first",
    "--no-entry",
    "-zstack-size=14752"
  ],
  "extra-files": ["src/runtime/asm_tinygowasm.S"]
}

Running with wasmer:

wasmer run ./tinygo-gc-debug.wasm --entrypoint boot

Traceback:

error: RuntimeError: unreachable
    at runtime.alloc (<module>[2]:0xe0)
    at boot (<module>[3]:0xfa)

from tinygo.

@orsinium can you please also try removing "-mno-bulk-memory"

from tinygo.

Running with wasmer:

wasmer run ./tinygo-gc-debug.wasm --entrypoint boot

Don't specify a different entrypoint. This likely causes the crash you're seeing. Just let _start be called (it initializes important data structures like the heap).

can you please also try removing "-mno-bulk-memory"

That's unlikely to have an effect, the only thing it does is change whether LLVM is allowed to use bulk memory instructions (it doesn't affect memory layout).

from tinygo.

can you please also try removing "-mno-bulk-memory"

Doesn't help.

Just let _start be called (it initializes important data structures like the heap).

There is no _start section in the generated wasm file:

❯ wasm-objdump -x --section=export ./tinygo-gc-debug.wasm

tinygo-gc-debug.wasm:	file format wasm 0x1

Section Details:

Export[3]:
 - memory[0] -> "memory"
 - func[1] <_initialize> -> "_initialize"
 - func[3] <boot> -> "boot"

Probably, because there is "--no-entry" specified in the target file. If I try removing it:

wasm-ld: error: entry symbol not defined (pass --no-entry to suppress): _start
failed to run tool: wasm-ld
error: failed to link /tmp/tinygo180852312/main: exit status 1

from tinygo.

It looks like you've modified some internals of TinyGo and are reporting issues as a result of that.
If you want us to help, I suggest you use either one of the built-in targets (like -target=wasi) or describe exactly the modifications you made and the platform you're targetting.

from tinygo.

The TinyGo compiler I use is not modified. I installed the artifact from this job: https://github.com/tinygo-org/tinygo/actions/runs/8469118660

I use a custom target.json which is attached to the issue and in the comment above. The wasm-unknown target expects the memory to be imported and the wasi target cannot be used with the environment that I target.

$ tinygo build -target=wasm-unknown .
$ wasmer run ./tinygo-gc-debug.wasm --entrypoint boot    
error: Unable to instantiate the WebAssembly module
╰─▶ 1: Error while importing "env"."memory": unknown import. Expected Memory(MemoryType { minimum: 2 pages, maximum: None, shared: false })

from tinygo.

Ok, in that case you need to make sure that the first thing that's called is _initialize. This exported function needs to be called before anything else to initialize the heap and various other important data structures.

from tinygo.