diff --git a/libc/Android.bp b/libc/Android.bp
index c101f45..99261f9 100644
--- a/libc/Android.bp
+++ b/libc/Android.bp
@@ -827,6 +827,7 @@
         riscv64: {
             srcs: [
                "arch-riscv64/string/__memset_chk.S",
+               "arch-riscv64/string/__memcpy_chk.S",
             ],
         },
     },
@@ -2307,6 +2308,11 @@
                 "arch-arm64/string/__memcpy_chk.S",
             ],
         },
+        riscv64: {
+            srcs: [
+               "arch-riscv64/string/__memcpy_chk.S",
+            ],
+        },
     },
     whole_static_libs: [
         "libarm-optimized-routines-mem",
diff --git a/libc/arch-riscv64/string/__memcpy_chk.S b/libc/arch-riscv64/string/__memcpy_chk.S
new file mode 100644
index 0000000..4a2d13d
--- /dev/null
+++ b/libc/arch-riscv64/string/__memcpy_chk.S
@@ -0,0 +1,9 @@
+#include <private/bionic_asm.h>
+
+ENTRY(__memcpy_chk)
+  bleu a2, a3, 1f
+  call __memcpy_chk_fail
+
+1:
+   tail memcpy
+END(__memcpy_chk)
diff --git a/libc/bionic/fortify.cpp b/libc/bionic/fortify.cpp
index 73cf973..7dee5e3 100644
--- a/libc/bionic/fortify.cpp
+++ b/libc/bionic/fortify.cpp
@@ -489,9 +489,9 @@
   return strcpy(dst, src);
 }
 
-#if !defined(__arm__) && !defined(__aarch64__)
+#if !defined(__arm__) && !defined(__aarch64__) && !defined(__riscv)
 // Runtime implementation of __memcpy_chk (used directly by compiler, not in headers).
-// arm32 and arm64 have assembler implementations, and don't need this C fallback.
+// arm32,arm64,riscv have assembler implementations, and don't need this C fallback.
 extern "C" void* __memcpy_chk(void* dst, const void* src, size_t count, size_t dst_len) {
   __check_count("memcpy", "count", count);
   __check_buffer_access("memcpy", "write into", count, dst_len);
diff --git a/libc/bionic/gwp_asan_wrappers.cpp b/libc/bionic/gwp_asan_wrappers.cpp
index 251633d..fab29ef 100644
--- a/libc/bionic/gwp_asan_wrappers.cpp
+++ b/libc/bionic/gwp_asan_wrappers.cpp
@@ -307,8 +307,10 @@
     sysprop_names[3] = persist_default_sysprop;
   }
 
+  // TODO(mitchp): Log overrides using this.
+  const char* source;
   return get_config_from_env_or_sysprops(env_var, sysprop_names, arraysize(sysprop_names),
-                                         value_out, PROP_VALUE_MAX);
+                                         value_out, PROP_VALUE_MAX, &source);
 }
 
 bool GetGwpAsanIntegerOption(unsigned long long* result,
diff --git a/libc/bionic/libc_init_static.cpp b/libc/bionic/libc_init_static.cpp
index d64d402..0935cd6 100644
--- a/libc/bionic/libc_init_static.cpp
+++ b/libc/bionic/libc_init_static.cpp
@@ -217,16 +217,13 @@
 // Returns true if there's an environment setting (either sysprop or env var)
 // that should overwrite the ELF note, and places the equivalent heap tagging
 // level into *level.
-static bool get_environment_memtag_setting(HeapTaggingLevel* level) {
+static bool get_environment_memtag_setting(const char* basename, HeapTaggingLevel* level) {
   static const char kMemtagPrognameSyspropPrefix[] = "arm64.memtag.process.";
   static const char kMemtagGlobalSysprop[] = "persist.arm64.memtag.default";
   static const char kMemtagOverrideSyspropPrefix[] =
       "persist.device_config.memory_safety_native.mode_override.process.";
 
-  const char* progname = __libc_shared_globals()->init_progname;
-  if (progname == nullptr) return false;
-
-  const char* basename = __gnu_basename(progname);
+  if (basename == nullptr) return false;
 
   char options_str[PROP_VALUE_MAX];
   char sysprop_name[512];
@@ -237,8 +234,9 @@
                            kMemtagOverrideSyspropPrefix, basename);
   const char* sys_prop_names[] = {sysprop_name, remote_sysprop_name, kMemtagGlobalSysprop};
 
+  const char* source = nullptr;
   if (!get_config_from_env_or_sysprops("MEMTAG_OPTIONS", sys_prop_names, arraysize(sys_prop_names),
-                                       options_str, sizeof(options_str))) {
+                                       options_str, sizeof(options_str), &source)) {
     return false;
   }
 
@@ -249,27 +247,35 @@
   } else if (strcmp("off", options_str) == 0) {
     *level = M_HEAP_TAGGING_LEVEL_TBI;
   } else {
-    async_safe_format_log(
-        ANDROID_LOG_ERROR, "libc",
-        "unrecognized memtag level: \"%s\" (options are \"sync\", \"async\", or \"off\").",
-        options_str);
+    async_safe_format_log(ANDROID_LOG_ERROR, "libc",
+                          "%s: unrecognized memtag level in %s: \"%s\" (options are \"sync\", "
+                          "\"async\", or \"off\").",
+                          basename, source, options_str);
     return false;
   }
-
+  async_safe_format_log(ANDROID_LOG_DEBUG, "libc", "%s: chose memtag level \"%s\" from %s.",
+                        basename, options_str, source);
   return true;
 }
 
+static void log_elf_memtag_level(const char* basename, const char* level) {
+  async_safe_format_log(ANDROID_LOG_DEBUG, "libc", "%s: chose memtag level \"%s\" from ELF note",
+                        basename ?: "<unknown>", level);
+}
+
 // Returns the initial heap tagging level. Note: This function will never return
 // M_HEAP_TAGGING_LEVEL_NONE, if MTE isn't enabled for this process we enable
 // M_HEAP_TAGGING_LEVEL_TBI.
 static HeapTaggingLevel __get_heap_tagging_level(const void* phdr_start, size_t phdr_ct,
                                                  uintptr_t load_bias, bool* stack) {
+  const char* progname = __libc_shared_globals()->init_progname;
+  const char* basename = progname ? __gnu_basename(progname) : nullptr;
   unsigned note_val =
       __get_memtag_note(reinterpret_cast<const ElfW(Phdr)*>(phdr_start), phdr_ct, load_bias);
   *stack = note_val & NT_MEMTAG_STACK;
 
   HeapTaggingLevel level;
-  if (get_environment_memtag_setting(&level)) return level;
+  if (get_environment_memtag_setting(basename, &level)) return level;
 
   // Note, previously (in Android 12), any value outside of bits [0..3] resulted
   // in a check-fail. In order to be permissive of further extensions, we
@@ -284,14 +290,17 @@
       // by anyone, but we note it (heh) here for posterity, in case the zero
       // level becomes meaningful, and binaries with this note can be executed
       // on Android 12 devices.
+      log_elf_memtag_level(basename, "off");
       return M_HEAP_TAGGING_LEVEL_TBI;
     case NT_MEMTAG_LEVEL_ASYNC:
+      log_elf_memtag_level(basename, "async");
       return M_HEAP_TAGGING_LEVEL_ASYNC;
     case NT_MEMTAG_LEVEL_SYNC:
     default:
       // We allow future extensions to specify mode 3 (currently unused), with
       // the idea that it might be used for ASYMM mode or something else. On
       // this version of Android, it falls back to SYNC mode.
+      log_elf_memtag_level(basename, "sync");
       return M_HEAP_TAGGING_LEVEL_SYNC;
   }
 }
diff --git a/libc/bionic/sysprop_helpers.cpp b/libc/bionic/sysprop_helpers.cpp
index 5627034..2051330 100644
--- a/libc/bionic/sysprop_helpers.cpp
+++ b/libc/bionic/sysprop_helpers.cpp
@@ -57,18 +57,22 @@
 }
 
 bool get_config_from_env_or_sysprops(const char* env_var_name, const char* const* sys_prop_names,
-                                     size_t sys_prop_names_size, char* options,
-                                     size_t options_size) {
+                                     size_t sys_prop_names_size, char* options, size_t options_size,
+                                     const char** chosen_source) {
   const char* env = getenv(env_var_name);
   if (env && *env != '\0') {
     strncpy(options, env, options_size);
     options[options_size - 1] = '\0';  // Ensure null-termination.
+    *chosen_source = env_var_name;
     return true;
   }
 
   for (size_t i = 0; i < sys_prop_names_size; ++i) {
     if (sys_prop_names[i] == nullptr) continue;
-    if (get_property_value(sys_prop_names[i], options, options_size)) return true;
+    if (get_property_value(sys_prop_names[i], options, options_size)) {
+      *chosen_source = sys_prop_names[i];
+      return true;
+    }
   }
   return false;
 }
diff --git a/libc/bionic/sysprop_helpers.h b/libc/bionic/sysprop_helpers.h
index a02c2dc..84e7af1 100644
--- a/libc/bionic/sysprop_helpers.h
+++ b/libc/bionic/sysprop_helpers.h
@@ -36,10 +36,13 @@
 //   2. System properties, in the order they're specified in sys_prop_names.
 // If neither of these options are specified (or they're both an empty string),
 // this function returns false. Otherwise, it returns true, and the presiding
-// options string is written to the `options` buffer of size `size`. If this
-// function returns true, `options` is guaranteed to be null-terminated.
+// options string is written to the `options` buffer of size `size`. It will
+// store a pointer to either env_var_name, or into the relevant entry of
+// sys_prop_names into choicen_source, indiciating which value was used. If
+// this function returns true, `options` is guaranteed to be null-terminated.
 // `options_size` should be at least PROP_VALUE_MAX.
 __LIBC_HIDDEN__ bool get_config_from_env_or_sysprops(const char* env_var_name,
                                                      const char* const* sys_prop_names,
                                                      size_t sys_prop_names_size, char* options,
-                                                     size_t options_size);
+                                                     size_t options_size,
+                                                     const char** chosen_source);