setDatatype writes host-endian integers to Wasm memory on big-endian (s390x)

[vinayakray19]

Summary

WasmBase::setDatatype in include/proxy-wasm/wasm.h writes primitive values to Wasm linear memory using raw setMemory without endian conversion. Wasm memory is always little-endian, but on big-endian hosts (e.g. s390x) the host writes native big-endian bytes.

This affects hostcalls that return integers via output pointers, including proxy_get_log_level (exports::get_log_level in src/exports.cc).

Impact

On s390x, Rust Wasm plugins calling proxy_get_log_level during proxy_on_configure can fail with:

Function: proxy_on_configure failed: Uncaught RuntimeError: memory access out of bounds

Similar failures were reported previously in #197; PR #198 fixed several endianness paths but setDatatype was not updated.

Root cause

setWord correctly uses htowasm before writing to Wasm memory:

uint32_t word32 = htowasm(word.u32(), true);
memcpy(memory_->data() + pointer, &word32, size);

setDatatype does not:

return wasm_vm_->setMemory(ptr, sizeof(T), &t);

setDatatype is used in many exports (get_log_level, get_metric, define_metric, get_current_time_nanoseconds, etc.).

Proposed fix

Convert to Wasm byte order before writing:

template <typename T> inline bool WasmBase::setDatatype(uint64_t ptr, const T &t) {
  T value = htowasm(t, wasm_vm_->usesWasmByteOrder());
  return wasm_vm_->setMemory(ptr, sizeof(T), &value);
}

Do not fix this in setMemory itself — that API is also used for opaque byte blobs (strings, random data, WASI structs).

Test plan

• Add regression test asserting setDatatype stores little-endian bytes in Wasm memory
• Verify on s390x CI (Wasmtime matrix job)

[vinayakray19]

Fix PR: #553

[vinayakray19]

/assign