[WasmFS] Fix FS.readFile + WASM_BIGINT (#17316)

_wasmfs_read_file wrote a 32-bit unsigned integer, while
makeGetValue in JS read this as a 64-bit integer.

This caused the length to be returned incorrectly when linking
with -sWASM_BIGINT.

Resolves: #17444.

Author: kleisauke

src/library_wasmfs.js

@@ -18,6 +18,7 @@ mergeInto(LibraryManager.library, {
     '$PATH',
     '$allocateUTF8',
     '$allocateUTF8OnStack',
+    '$readI53FromI64',
   ],
   $FS : {
     // TODO: Clean up the following functions - currently copied from library_fs.js directly.
@@ -88,8 +89,8 @@ mergeInto(LibraryManager.library, {
 
       // Copy the file into a JS buffer on the heap.
       var buf = __wasmfs_read_file(pathName);
-      // The integer length is returned in the first 8 bytes of the buffer.
-      var length = {{{ makeGetValue('buf', '0', 'i64') }}};
+      // The signed integer length resides in the first 8 bytes of the buffer.
+      var length = {{{ makeGetValue('buf', '0', 'i53') }}};
 
       // Default return type is binary.
       // The buffer contents exist 8 bytes after the returned pointer.

src/parseTools.js

@@ -408,6 +408,9 @@ function makeGetValue(ptr, pos, type, noNeedFirst, unsigned, ignore, align) {
   }
 
   const offset = calcFastOffset(ptr, pos, noNeedFirst);
+  if (type === 'i53' || type === 'u53') {
+    return 'readI53From' + (unsigned ? 'U' : 'I') + '64(' + offset + ')';
+  }
 
   const slab = getHeapForType(type);
   let ret = slab + '[' + getHeapOffset(offset, type) + ']';

system/lib/wasmfs/js_api.cpp

@@ -22,6 +22,8 @@ __wasi_fd_t wasmfs_create_file(char* pathname, mode_t mode, backend_t backend);
 // The buffer will also contain the file length.
 // Caller must free the returned pointer.
 void* _wasmfs_read_file(char* path) {
+  static_assert(sizeof(off_t) == 8, "File offset type must be 64-bit");
+
   struct stat file;
   int err = 0;
   err = stat(path, &file);
@@ -34,8 +36,8 @@ void* _wasmfs_read_file(char* path) {
   // first 8 bytes. The remaining bytes will contain the buffer contents. This
   // allows the caller to use HEAPU8.subarray(buf + 8, buf + 8 + length).
   off_t size = file.st_size;
-  uint8_t* result = (uint8_t*)malloc((size + sizeof(size)));
-  *(uint32_t*)result = size;
+  uint8_t* result = (uint8_t*)malloc(size + sizeof(size));
+  *(off_t*)result = size;
 
   int fd = open(path, O_RDONLY);
   if (fd < 0) {

tests/test_other.py

@@ -11865,6 +11865,12 @@ def test_wasmfs_getdents(self):
   def test_wasmfs_readfile(self):
     self.do_run_in_out_file_test(test_file('wasmfs/wasmfs_readfile.c'))
 
+  @wasmfs_all_backends
+  def test_wasmfs_readfile_bigint(self):
+    self.set_setting('WASM_BIGINT')
+    self.node_args += ['--experimental-wasm-bigint']
+    self.do_run_in_out_file_test(test_file('wasmfs/wasmfs_readfile.c'))
+
   def test_wasmfs_jsfile(self):
     self.set_setting('WASMFS')
     self.do_run_in_out_file_test('wasmfs/wasmfs_jsfile.c')

tests/wasmfs/wasmfs_readfile.c

@@ -11,6 +11,7 @@
 #include <errno.h>
 #include <fcntl.h>
 #include <stdio.h>
+#include <stdlib.h>
 #include <string.h>
 #include <unistd.h>
 
@@ -25,10 +26,13 @@ int main() {
   errno = 0;
   write(fd, msg, strlen(msg));
   assert(errno == 0);
+  err = close(fd);
+  assert(err == 0);
 
   EM_ASM({
-    var output = FS.readFile("/root/test", {encoding : 'utf8'});
-    out(output);
+    var output = FS.readFile("/root/test");
+    out(UTF8ArrayToString(output, 0));
+    out("Length: " + output.byteLength);
   });
 
   EM_ASM({

tests/wasmfs/wasmfs_readfile.out

@@ -1,5 +1,6 @@
 Success
 
+Length: 8
 Fatal error in FS.readFile
 Aborted(native code called abort())
 Fatal error in FS.readFile