gh-127146: Report uid in Emscripten + node as native uid (#136509)

Corrects the handling of getuid on emscripten, which was consistently reporting as 0.

Author: hoodmane

Python/emscripten_syscalls.c

@@ -0,0 +1,19 @@
+#include "emscripten.h"
+
+// If we're running in node, report the UID of the user in the native system as
+// the UID of the user. Since the nodefs will report the uid correctly, if we
+// don't make getuid report it correctly too we'll see some permission errors.
+// Normally __syscall_getuid32 is a stub that always returns 0 but it is
+// defined with weak linkage so we can override it.
+EM_JS(int, __syscall_getuid32_js, (void), {
+    // If we're in node and we can, report the native uid
+    if (typeof process !== "undefined" && typeof process.getuid === "function") {
+        return process.getuid();
+    }
+    // Fall back to the stub case of returning 0.
+    return 0;
+})
+
+int __syscall_getuid32(void) {
+    return __syscall_getuid32_js();
+}

Tools/c-analyzer/cpython/_parser.py

@@ -66,6 +66,7 @@ def clean_lines(text):
 Python/dynload_dl.c             # dl.h
 Python/dynload_hpux.c           # dl.h
 Python/emscripten_signal.c
+Python/emscripten_syscalls.c
 Python/thread_pthread.h
 Python/thread_pthread_stubs.h
 

configure

@@ -5121,7 +5121,7 @@ PLATFORM_OBJS=
 
 AS_CASE([$ac_sys_system],
   [Emscripten], [
-    AS_VAR_APPEND([PLATFORM_OBJS], [' Python/emscripten_signal.o Python/emscripten_trampoline.o'])
+    AS_VAR_APPEND([PLATFORM_OBJS], [' Python/emscripten_signal.o Python/emscripten_trampoline.o Python/emscripten_syscalls.o'])
     AS_VAR_APPEND([PLATFORM_HEADERS], [' $(srcdir)/Include/internal/pycore_emscripten_signal.h $(srcdir)/Include/internal/pycore_emscripten_trampoline.h'])
   ],
 )