gh-145177: Bump Emscripten to 6.0.0

And fix two problems due to changes in Emscripten libc:

1. There was a regression in getentropy that broke it if exactly one byte is
requested. Replace it with a wrapped getentropy that replaces a one byte request
with a two-byte request and then put the first byte in the original buffer.
2. Emscripten libc now supports umask. We need to initialize the emscripten
libc umask to the ambient umask and zero out the ambient umask.

Author: hoodmane

Lib/test/test_platform.py

@@ -534,7 +534,20 @@ def test_ios_ver(self):
 
     def test_libc_ver(self):
         if support.is_emscripten:
-            assert platform.libc_ver() == ("emscripten", "4.0.19")
+            import tomllib
+            from pathlib import Path
+
+            # Get expected emscripten version from emscripten config
+            config_path = (
+                Path(__file__).parents[2] / "Platforms/emscripten/config.toml"
+            )
+            with open(config_path, "rb") as fp:
+                emscripten_version = tomllib.load(fp)["emscripten-version"]
+
+            self.assertEqual(
+                platform.libc_ver(), ("emscripten", emscripten_version)
+            )
+
             return
         # check that libc_ver(executable) doesn't raise an exception
         if os.path.isdir(sys.executable) and \

Platforms/emscripten/config.toml

@@ -1,7 +1,7 @@
 # Any data that can vary between Python versions is to be kept in this file.
 # This allows for blanket copying of the Emscripten build code between supported
 # Python versions.
-emscripten-version = "4.0.19"
+emscripten-version = "6.0.0"
 node-version = "24"
 test-args = [
     "-m", "test",

Python/emscripten_syscalls.c

@@ -23,24 +23,27 @@ int __syscall_getuid32(void) {
     return __syscall_getuid32_js();
 }
 
-EM_JS(int, __syscall_umask_js, (int mask), {
-    // If we're in node and we can, call native process.umask()
+// Emscripten's syscall layer tracks the umask in SYSCALLS.currentUmask and
+// applies it itself when creating files and directories. We mount the real
+// filesystem via NODEFS, which applies proces.umask() to everything as well. To
+// avoid masking the mode twice, read and zero out process umask at startup,
+// and store it as emscripten's umask.
+EM_JS(void, __syscall_init_umask_js, (void), {
     if (ENVIRONMENT_IS_NODE) {
         try {
-            return process.umask(mask);
-        } catch(e) {
-            // oops...
-            // NodeJS docs: "In Worker threads, process.umask(mask) will throw an exception."
-            // umask docs: "This system call always succeeds"
-            return 0;
+            // process.umask(0) returns the previous umask and sets it to 0.
+            SYSCALLS.currentUmask = process.umask(0);
+        } catch (e) {
+            // NodeJS docs: "In Worker threads, process.umask(mask) will throw an
+            // exception." In that case just keep emscripten's default umask.
         }
     }
-    // Fall back to the stub case of returning 0.
-    return 0;
 })
 
-int __syscall_umask(int mask) {
-    return __syscall_umask_js(mask);
+EM_JS_DEPS(__syscall_init_umask, "$SYSCALLS");
+
+__attribute__((constructor)) void __syscall_init_umask(void) {
+    __syscall_init_umask_js();
 }
 
 #include <wasi/api.h>
@@ -290,6 +293,26 @@ int __syscall_poll(intptr_t fds, int nfds, int timeout) {
     return __block_for_int(p);
 }
 
+
+// Workaround for an Emscripten bug: getentropy(buffer, 1) returns the single
+// byte of entropy as the return code. Fixed upstream by
+// emscripten-core/emscripten#27122
+int __real_getentropy(void*, size_t);
+
+int __wrap_getentropy(void *buffer, size_t len) {
+    if (len != 1) {
+        return __real_getentropy(buffer, len);
+    }
+    // Length is 1. Workaround is to get two bytes of entropy and write the
+    // first one into the original target buffer.
+    uint8_t tmp[2];
+    int ret = __real_getentropy(tmp, 2);
+    if (ret == 0) {
+        *(uint8_t *)buffer = tmp[0];
+    }
+    return ret;
+}
+
 #include <sys/ioctl.h>
 
 int syscall_ioctl_orig(int fd, int request, void* varargs)

configure

@@ -2411,6 +2411,10 @@ AS_CASE([$ac_sys_system],
     dnl Avoid bugs in JS fallback string decoding path
     AS_VAR_APPEND([LINKFORSHARED], [" -sTEXTDECODER=2"])
 
+    dnl Workaround for a bug in Emscipten libc's getentropy. See
+    dnl __wrap_getentropy in Python/emscripten_syscalls.c.
+    AS_VAR_APPEND([LDFLAGS_NODIST], [" -Wl,--wrap=getentropy"])
+
     AS_VAR_IF([enable_wasm_dynamic_linking], [yes], [
       AS_VAR_APPEND([LINKFORSHARED], [" -sMAIN_MODULE"])
     ])