Bug

When building any program that transitively depends on crypto/internal/fips140/drbg
(e.g. crypto/ecdsa, crypto/rsa) for the wasm target with TinyGo + Go 1.26,
the produced app.wasm imports gojs.runtime.getRandomData, but
targets/wasm_exec.js does not provide an implementation. The module fails
to instantiate at runtime with:

LinkError: WebAssembly.instantiate(): Import #13 "gojs" "runtime.getRandomData": function import requires a callable

Background

• In Go 1.26, crypto/rand.Read routes through crypto/internal/fips140/drbg.Read,
  which seeds itself from crypto/internal/sysrand.Read.
• On js/wasm, crypto/internal/sysrand declares

  //go:wasmimport gojs runtime.getRandomData
  //go:noescape
  func getRandomValues(r []byte)

  (see crypto/internal/sysrand/rand_js.go)
• PR compiler: crypto/internal/sysrand is allowed to use unsafe signatures #4784 made the unsafe-signature []byte import compile, but the
  corresponding JS-side implementation was never added to targets/wasm_exec.js.
• Related: crypto/sha256 //go:wasmimport gojs runtime.getRandomData: unsupported parameter type []byte #4777 (compile-side, fixed in 0.37.0; runtime side never addressed).

Reproducer

go.mod

module repro

go 1.26

main.go

package main

import (
	"crypto/ecdsa"
	"crypto/elliptic"
	"crypto/rand"
)

func main() {
	_, err := ecdsa.GenerateKey(elliptic.P256(), rand.Reader)
	if err != nil {
		println("err:", err.Error())
		return
	}
	println("ok")
}

$ tinygo version
tinygo version 0.41.1 darwin/arm64 (using go version go1.26.2 and LLVM version 20.1.1)

$ tinygo build -target wasm -no-debug -o app.wasm .

$ wasm-objdump -j Import -x app.wasm | grep getRandomData
 - func[13] sig=7 <crypto/internal/sysrand.getRandomValues> <- gojs.runtime.getRandomData

$ cp $(tinygo env TINYGOROOT)/targets/wasm_exec.js .
$ node wasm_exec.js app.wasm
[LinkError: WebAssembly.instantiate(): Import #13 "gojs" "runtime.getRandomData": function import requires a callable]

Expected

node wasm_exec.js app.wasm should print ok and exit 0.

Suggested fix

Add the missing import to the gojs block of targets/wasm_exec.js. The
upstream Go signature is func getRandomValues(r []byte), which TinyGo's
WASM C ABI passes as (ptr i32, len i32, cap i32) -> nil. The
Crypto.getRandomValues Web API has a 64 KiB per-call limit, so we chunk:

gojs: {
    // func getRandomData(r []byte)
    "runtime.getRandomData": (slice_ptr, slice_len, slice_cap) => {
        const buf = loadSlice(slice_ptr, slice_len, slice_cap);
        // crypto.getRandomValues has a 65536-byte cap per call
        for (let offset = 0; offset < buf.length; offset += 65536) {
            crypto.getRandomValues(
                buf.subarray(offset, Math.min(offset + 65536, buf.length))
            );
        }
    },
    // ...existing imports below...
}

Verification

After applying the patch above to targets/wasm_exec.js:

$ node wasm_exec.js app.wasm
ok

Environment

I'm happy to send a PR if this analysis looks correct.