emscripten-core · sbc100 · Sep 4, 2026 · Sep 2, 2026
diff --git a/system/lib/libc/emscripten_memset.c b/system/lib/libc/emscripten_memset.c
@@ -1,30 +1,37 @@
-#include "emscripten_internal.h" // for emscripten_memset_big
-
-#if defined(__has_feature) && __has_feature(address_sanitizer)
-// build an uninstrumented version of memset
-__attribute__((no_sanitize("address"))) void *__musl_memset(void *str, int c, size_t n);
-__attribute__((no_sanitize("address"))) void *__memset(void *str, int c, size_t n);
-#endif
-
-__attribute__((__weak__)) void *__musl_memset(void *str, int c, size_t n);
-__attribute__((__weak__)) void *__memset(void *str, int c, size_t n);
+/*
+ * Copyright 2019 The Emscripten Authors.  All rights reserved.
+ * Emscripten is available under two separate licenses, the MIT license and the
+ * University of Illinois/NCSA Open Source License.  Both these licenses can be
+ * found in the LICENSE file.
+ */
+
+
+#include <stdint.h>
+#include <string.h>
+#include "libc.h"
+
+// Use the simple/naive version of memset when building with asan.
+// Note: ASan's shadow memory poisoner calls REAL(memset) directly on shadow
+// memory, so this must remain uninstrumented to prevent ASan from checking
+// the shadow memory of the shadow memory itself.
+#if __has_feature(address_sanitizer)
+
+static __attribute__((no_sanitize("address"))) void *__memset(void *dest, int c, size_t n) {
+  unsigned char *d = (unsigned char *)dest;
+  while (n--) *d++ = (unsigned char)c;
+  return dest;
+}
 
-#if defined(EMSCRIPTEN_OPTIMIZE_FOR_OZ)
+#else
 
-void *__memset(void *str, int c, size_t n) {
+static void *__memset(void *dest, int c, size_t n) {
   // memory.fill traps on OOB zero-length sets, but memset must not.
   if (n) {
-    __builtin_wasm_memory_fill(0, str, c, n);
+    __builtin_wasm_memory_fill(0, dest, c, n);
   }
-  return str;
+  return dest;
 }
 
-#else
-
-#define memset __memset
-#include "musl/src/string/memset.c"
-#undef memset
-
 #endif
 
 weak_alias(__memset, emscripten_builtin_memset);

diff --git a/system/lib/libc/musl/src/string/memcmp.c b/system/lib/libc/musl/src/string/memcmp.c
@@ -1,4 +1,4 @@
-#if __EMSCRIPTEN__
+#ifdef __EMSCRIPTEN__
 #include <stdint.h>
 #endif
 #include <string.h>

diff --git a/test/codesize/test_codesize_cxx_ctors1.json b/test/codesize/test_codesize_cxx_ctors1.json
@@ -1,10 +1,10 @@
 {
   "a.out.js": 19224,
   "a.out.js.gz": 8124,
-  "a.out.nodebug.wasm": 134250,
-  "a.out.nodebug.wasm.gz": 51364,
-  "total": 153474,
-  "total_gz": 59488,
+  "a.out.nodebug.wasm": 133897,
+  "a.out.nodebug.wasm.gz": 51215,
+  "total": 153121,
+  "total_gz": 59339,
   "sent": [
     "__cxa_throw",
     "_abort_js",

diff --git a/test/codesize/test_codesize_cxx_ctors2.json b/test/codesize/test_codesize_cxx_ctors2.json
@@ -1,10 +1,10 @@
 {
   "a.out.js": 19201,
   "a.out.js.gz": 8107,
-  "a.out.nodebug.wasm": 133679,
-  "a.out.nodebug.wasm.gz": 51045,
-  "total": 152880,
-  "total_gz": 59152,
+  "a.out.nodebug.wasm": 133326,
+  "a.out.nodebug.wasm.gz": 50903,
+  "total": 152527,
+  "total_gz": 59010,
   "sent": [
     "__cxa_throw",
     "_abort_js",

diff --git a/test/codesize/test_codesize_cxx_except.json b/test/codesize/test_codesize_cxx_except.json
@@ -1,10 +1,10 @@
 {
   "a.out.js": 22917,
   "a.out.js.gz": 9078,
-  "a.out.nodebug.wasm": 176707,
-  "a.out.nodebug.wasm.gz": 58892,
-  "total": 199624,
-  "total_gz": 67970,
+  "a.out.nodebug.wasm": 176354,
+  "a.out.nodebug.wasm.gz": 58741,
+  "total": 199271,
+  "total_gz": 67819,
   "sent": [
     "__cxa_begin_catch",
     "__cxa_end_catch",

diff --git a/test/codesize/test_codesize_cxx_except_wasm.json b/test/codesize/test_codesize_cxx_except_wasm.json
@@ -1,10 +1,10 @@
 {
   "a.out.js": 19023,
   "a.out.js.gz": 8039,
-  "a.out.nodebug.wasm": 149967,
-  "a.out.nodebug.wasm.gz": 56437,
-  "total": 168990,
-  "total_gz": 64476,
+  "a.out.nodebug.wasm": 149614,
+  "a.out.nodebug.wasm.gz": 56302,
+  "total": 168637,
+  "total_gz": 64341,
   "sent": [
     "_abort_js",
     "_tzset_js",

diff --git a/test/codesize/test_codesize_cxx_except_wasm_legacy.json b/test/codesize/test_codesize_cxx_except_wasm_legacy.json
@@ -1,10 +1,10 @@
 {
   "a.out.js": 19101,
   "a.out.js.gz": 8065,
-  "a.out.nodebug.wasm": 147749,
-  "a.out.nodebug.wasm.gz": 56113,
-  "total": 166850,
-  "total_gz": 64178,
+  "a.out.nodebug.wasm": 147396,
+  "a.out.nodebug.wasm.gz": 55982,
+  "total": 166497,
+  "total_gz": 64047,
   "sent": [
     "_abort_js",
     "_tzset_js",

diff --git a/test/codesize/test_codesize_cxx_mangle.json b/test/codesize/test_codesize_cxx_mangle.json
@@ -1,10 +1,10 @@
 {
   "a.out.js": 22967,
   "a.out.js.gz": 9098,
-  "a.out.nodebug.wasm": 242987,
-  "a.out.nodebug.wasm.gz": 81112,
-  "total": 265954,
-  "total_gz": 90210,
+  "a.out.nodebug.wasm": 242634,
+  "a.out.nodebug.wasm.gz": 80968,
+  "total": 265601,
+  "total_gz": 90066,
   "sent": [
     "__cxa_begin_catch",
     "__cxa_end_catch",

diff --git a/test/codesize/test_codesize_cxx_noexcept.json b/test/codesize/test_codesize_cxx_noexcept.json
@@ -1,10 +1,10 @@
 {
   "a.out.js": 19224,
   "a.out.js.gz": 8124,
-  "a.out.nodebug.wasm": 136160,
-  "a.out.nodebug.wasm.gz": 51987,
-  "total": 155384,
-  "total_gz": 60111,
+  "a.out.nodebug.wasm": 135807,
+  "a.out.nodebug.wasm.gz": 51835,
+  "total": 155031,
+  "total_gz": 59959,
   "sent": [
     "__cxa_throw",
     "_abort_js",

diff --git a/test/codesize/test_codesize_cxx_wasmfs.json b/test/codesize/test_codesize_cxx_wasmfs.json
@@ -1,10 +1,10 @@
 {
   "a.out.js": 6604,
   "a.out.js.gz": 3154,
-  "a.out.nodebug.wasm": 173886,
-  "a.out.nodebug.wasm.gz": 64740,
-  "total": 180490,
-  "total_gz": 67894,
+  "a.out.nodebug.wasm": 173533,
+  "a.out.nodebug.wasm.gz": 64593,
+  "total": 180137,
+  "total_gz": 67747,
   "sent": [
     "__cxa_throw",
     "_abort_js",

diff --git a/test/codesize/test_codesize_hello_O0.json b/test/codesize/test_codesize_hello_O0.json
@@ -1,10 +1,10 @@
 {
   "a.out.js": 23471,
   "a.out.js.gz": 8555,
-  "a.out.nodebug.wasm": 14578,
-  "a.out.nodebug.wasm.gz": 7228,
-  "total": 38049,
-  "total_gz": 15783,
+  "a.out.nodebug.wasm": 14228,
+  "a.out.nodebug.wasm.gz": 7062,
+  "total": 37699,
+  "total_gz": 15617,
   "sent": [
     "fd_write"
   ],

diff --git a/test/codesize/test_codesize_hello_dylink.json b/test/codesize/test_codesize_hello_dylink.json
@@ -1,10 +1,10 @@
 {
   "a.out.js": 26258,
   "a.out.js.gz": 11211,
-  "a.out.nodebug.wasm": 17365,
-  "a.out.nodebug.wasm.gz": 8831,
-  "total": 43623,
-  "total_gz": 20042,
+  "a.out.nodebug.wasm": 17009,
+  "a.out.nodebug.wasm.gz": 8683,
+  "total": 43267,
+  "total_gz": 19894,
   "sent": [
     "__syscall_stat64",
     "emscripten_resize_heap",
@@ -37,7 +37,6 @@
     "$__emscripten_stdout_close",
     "$__emscripten_stdout_seek",
     "$__fwritex",
-    "$__memset",
     "$__stdio_write",
     "$__strchrnul",
     "$__towrite",

diff --git a/test/codesize/test_codesize_hello_dylink_all.json b/test/codesize/test_codesize_hello_dylink_all.json
@@ -1,7 +1,7 @@
 {
   "a.out.js": 270584,
-  "a.out.nodebug.wasm": 588564,
-  "total": 859148,
+  "a.out.nodebug.wasm": 588324,
+  "total": 858908,
   "sent": [
     "IMG_Init",
     "IMG_Load",
@@ -2134,7 +2134,6 @@
     "__ltsf2",
     "__lttf2",
     "__lxstat",
-    "__memset",
     "__mo_lookup",
     "__moddi3",
     "__modsi3",

diff --git a/test/codesize/test_unoptimized_code_size.json b/test/codesize/test_unoptimized_code_size.json
@@ -1,16 +1,16 @@
 {
   "hello_world.js": 54465,
   "hello_world.js.gz": 17297,
-  "hello_world.wasm": 14578,
-  "hello_world.wasm.gz": 7228,
+  "hello_world.wasm": 14228,
+  "hello_world.wasm.gz": 7062,
   "no_asserts.js": 23544,
   "no_asserts.js.gz": 8261,
-  "no_asserts.wasm": 11692,
-  "no_asserts.wasm.gz": 5768,
+  "no_asserts.wasm": 11342,
+  "no_asserts.wasm.gz": 5611,
   "strict.js": 51616,
   "strict.js.gz": 16308,
-  "strict.wasm": 14578,
-  "strict.wasm.gz": 7223,
-  "total": 170473,
-  "total_gz": 62085
+  "strict.wasm": 14228,
+  "strict.wasm.gz": 7061,
+  "total": 169423,
+  "total_gz": 61600
 }
diff --git a/tools/native_sigs.py b/tools/native_sigs.py
@@ -303,7 +303,6 @@
   '__map_file': 'ppp',
   '__math_invalidl': '_p__',
   '__memrchr': 'pp_p',
-  '__memset': 'pp_p',
   '__mkostemps': '_p__',
   '__mmap': 'ppp____',
   '__mo_lookup': 'pppp',

diff --git a/tools/system_libs.py b/tools/system_libs.py
@@ -1442,19 +1442,10 @@ def __init__(self, **kwargs):
 
   def get_libcall_files(self):
     # see comments in libc.customize_build_cmd
-
-    # some files also appear in libc, and a #define affects them
-    mem_files = files_in_path(
-      path='system/lib/libc',
-      filenames=['emscripten_memset.c'])
-
-    # some functions have separate files
-    math_files = files_in_path(
+    return files_in_path(
       path='system/lib/libc/musl/src/math',
       filenames=['pow_small.c', 'log_small.c', 'log2_small.c'])
 
-    return mem_files + math_files
-
   def get_files(self):
     libcall_files = self.get_libcall_files()