Do not reverse bytes for nullvm

This fixes the following istio proxy test on s390x:
https://github.com/istio/proxy/blob/master/test/envoye2e/tcp_metadata_exchange/tcp_metadata_exchange_test.go

Signed-off-by: Konstantin Maksimov <[email protected]>

Author: knm3000

include/proxy-wasm/exports.h

@@ -74,12 +74,13 @@ template <typename Pairs> size_t pairsSize(const Pairs &result) {
 
 template <typename Pairs> void marshalPairs(const Pairs &result, char *buffer) {
   char *b = buffer;
-  *reinterpret_cast<uint32_t *>(b) = htowasm(result.size());
+  bool reverse = "null" != contextOrEffectiveContext()->wasmVm()->getEngineName();
+  *reinterpret_cast<uint32_t *>(b) = reverse ? htowasm(result.size()) : result.size();
   b += sizeof(uint32_t);
   for (auto &p : result) {
-    *reinterpret_cast<uint32_t *>(b) = htowasm(p.first.size());
+    *reinterpret_cast<uint32_t *>(b) = reverse ? htowasm(p.first.size()) : p.first.size();
     b += sizeof(uint32_t);
-    *reinterpret_cast<uint32_t *>(b) = htowasm(p.second.size());
+    *reinterpret_cast<uint32_t *>(b) = reverse ? htowasm(p.second.size()) : p.second.size();
     b += sizeof(uint32_t);
   }
   for (auto &p : result) {

src/exports.cc

@@ -65,16 +65,22 @@ Pairs toPairs(std::string_view buffer) {
   if (buffer.size() < sizeof(uint32_t)) {
     return {};
   }
-  auto size = wasmtoh(*reinterpret_cast<const uint32_t *>(b));
+  bool reverse = "null" != contextOrEffectiveContext()->wasmVm()->getEngineName();
+  auto size = reverse ? wasmtoh(*reinterpret_cast<const uint32_t *>(b))
+                      : *reinterpret_cast<const uint32_t *>(b);
   b += sizeof(uint32_t);
   if (sizeof(uint32_t) + size * 2 * sizeof(uint32_t) > buffer.size()) {
     return {};
   }
   result.resize(size);
   for (uint32_t i = 0; i < size; i++) {
-    result[i].first = std::string_view(nullptr, wasmtoh(*reinterpret_cast<const uint32_t *>(b)));
+    result[i].first =
+        std::string_view(nullptr, reverse ? wasmtoh(*reinterpret_cast<const uint32_t *>(b))
+                                          : *reinterpret_cast<const uint32_t *>(b));
     b += sizeof(uint32_t);
-    result[i].second = std::string_view(nullptr, wasmtoh(*reinterpret_cast<const uint32_t *>(b)));
+    result[i].second =
+        std::string_view(nullptr, reverse ? wasmtoh(*reinterpret_cast<const uint32_t *>(b))
+                                          : *reinterpret_cast<const uint32_t *>(b));
     b += sizeof(uint32_t);
   }
   for (auto &p : result) {
@@ -691,6 +697,7 @@ Word wasi_unstable_fd_prestat_dir_name(Word /*fd*/, Word /*path_ptr*/, Word /*pa
 // logs.
 Word writevImpl(Word fd, Word iovs, Word iovs_len, Word *nwritten_ptr) {
   auto *context = contextOrEffectiveContext();
+  bool reverse = "null" != context->wasmVm()->getEngineName();
 
   // Read syscall args.
   uint64_t log_level;
@@ -714,8 +721,9 @@ Word writevImpl(Word fd, Word iovs, Word iovs_len, Word *nwritten_ptr) {
     }
     const auto *iovec = reinterpret_cast<const uint32_t *>(memslice.value().data());
     if (iovec[1] != 0U /* buf_len */) {
-      memslice = context->wasmVm()->getMemory(wasmtoh(iovec[0]) /* buf */,
-                                              wasmtoh(iovec[1]) /* buf_len */);
+      auto iovec0 = reverse ? wasmtoh(iovec[0]) : iovec[0];
+      auto iovec1 = reverse ? wasmtoh(iovec[1]) : iovec[1];
+      memslice = context->wasmVm()->getMemory(iovec0 /* buf */, iovec1 /* buf_len */);
       if (!memslice) {
         return 21; // __WASI_EFAULT
       }