diff --git a/bootstraptest/test_ractor.rb b/bootstraptest/test_ractor.rb
index bec742da4be0d5..af739ba4bc7fd7 100644
--- a/bootstraptest/test_ractor.rb
+++ b/bootstraptest/test_ractor.rb
@@ -1116,6 +1116,23 @@ class C
   end.value
 RUBY
 
+# Inserting into the id2ref table should be Ractor-safe
+assert_equal 'ok', <<~'RUBY'
+  # Force all calls to Kernel#object_id to insert into the id2ref table
+  ObjectSpace._id2ref(Object.new.object_id)
+
+  10.times.map do
+    Ractor.new do
+      10_000.times do
+        a = Object.new
+        a.object_id
+      end
+    end
+  end.map(&:value)
+
+  :ok
+RUBY
+
 # Ractor.make_shareable(obj)
 assert_equal 'true', <<~'RUBY', frozen_string_literal: false
   class C
diff --git a/ext/date/date_core.c b/ext/date/date_core.c
index cf8ea3c0a44990..6bcf272b62d8b0 100644
--- a/ext/date/date_core.c
+++ b/ext/date/date_core.c
@@ -9496,6 +9496,7 @@ Init_date_core(void)
     sym_zone = ID2SYM(rb_intern_const("zone"));
 
     half_days_in_day = rb_rational_new2(INT2FIX(1), INT2FIX(2));
+    rb_gc_register_mark_object(half_days_in_day);
 
 #if (LONG_MAX / DAY_IN_SECONDS) > SECOND_IN_NANOSECONDS
     day_in_nanoseconds = LONG2NUM((long)DAY_IN_SECONDS *
@@ -9507,8 +9508,6 @@ Init_date_core(void)
     day_in_nanoseconds = f_mul(INT2FIX(DAY_IN_SECONDS),
 			       INT2FIX(SECOND_IN_NANOSECONDS));
 #endif
-
-    rb_gc_register_mark_object(half_days_in_day);
     rb_gc_register_mark_object(day_in_nanoseconds);
 
     positive_inf = +INFINITY;
diff --git a/ext/openssl/ossl.c b/ext/openssl/ossl.c
index a19ff23b107c88..5fd6bff98b7bbe 100644
--- a/ext/openssl/ossl.c
+++ b/ext/openssl/ossl.c
@@ -122,7 +122,7 @@ ossl_buf2str(char *buf, int len)
 }
 
 void
-ossl_bin2hex(unsigned char *in, char *out, size_t inlen)
+ossl_bin2hex(const unsigned char *in, char *out, size_t inlen)
 {
     const char *hex = "0123456789abcdef";
     size_t i;
diff --git a/ext/openssl/ossl.h b/ext/openssl/ossl.h
index 93deafb4b68363..0b479a7200a1f4 100644
--- a/ext/openssl/ossl.h
+++ b/ext/openssl/ossl.h
@@ -131,7 +131,7 @@ do{\
  * Convert binary string to hex string. The caller is responsible for
  * ensuring out has (2 * len) bytes of capacity.
  */
-void ossl_bin2hex(unsigned char *in, char *out, size_t len);
+void ossl_bin2hex(const unsigned char *in, char *out, size_t len);
 
 /*
  * Our default PEM callback
diff --git a/ext/openssl/ossl_asn1.c b/ext/openssl/ossl_asn1.c
index b21a79484ccc4a..628140a75e3ea4 100644
--- a/ext/openssl/ossl_asn1.c
+++ b/ext/openssl/ossl_asn1.c
@@ -114,7 +114,8 @@ ossl_time_split(VALUE time, time_t *sec, int *days)
 VALUE
 asn1str_to_str(const ASN1_STRING *str)
 {
-    return rb_str_new((const char *)str->data, str->length);
+    return rb_str_new((const char *)ASN1_STRING_get0_data(str),
+                      ASN1_STRING_length(str));
 }
 
 /*
@@ -129,9 +130,8 @@ asn1integer_to_num(const ASN1_INTEGER *ai)
     if (!ai) {
         ossl_raise(rb_eTypeError, "ASN1_INTEGER is NULL!");
     }
-    if (ai->type == V_ASN1_ENUMERATED)
-        /* const_cast: workaround for old OpenSSL */
-        bn = ASN1_ENUMERATED_to_BN((ASN1_ENUMERATED *)ai, NULL);
+    if (ASN1_STRING_type(ai) == V_ASN1_ENUMERATED)
+        bn = ASN1_ENUMERATED_to_BN(ai, NULL);
     else
         bn = ASN1_INTEGER_to_BN(ai, NULL);
 
diff --git a/ext/openssl/ossl_ns_spki.c b/ext/openssl/ossl_ns_spki.c
index 1d1498824620a9..8440c2ee82b909 100644
--- a/ext/openssl/ossl_ns_spki.c
+++ b/ext/openssl/ossl_ns_spki.c
@@ -230,13 +230,12 @@ ossl_spki_get_challenge(VALUE self)
     NETSCAPE_SPKI *spki;
 
     GetSPKI(self, spki);
-    if (spki->spkac->challenge->length <= 0) {
+    if (ASN1_STRING_length(spki->spkac->challenge) <= 0) {
         OSSL_Debug("Challenge.length <= 0?");
         return rb_str_new(0, 0);
     }
 
-    return rb_str_new((const char *)spki->spkac->challenge->data,
-                      spki->spkac->challenge->length);
+    return asn1str_to_str(spki->spkac->challenge);
 }
 
 /*
diff --git a/ext/openssl/ossl_ocsp.c b/ext/openssl/ossl_ocsp.c
index 97ab24c347b556..93d8bc85671eac 100644
--- a/ext/openssl/ossl_ocsp.c
+++ b/ext/openssl/ossl_ocsp.c
@@ -1550,8 +1550,9 @@ ossl_ocspcid_get_issuer_name_hash(VALUE self)
     GetOCSPCertId(self, id);
     OCSP_id_get0_info(&name_hash, NULL, NULL, NULL, id);
 
-    ret = rb_str_new(NULL, name_hash->length * 2);
-    ossl_bin2hex(name_hash->data, RSTRING_PTR(ret), name_hash->length);
+    ret = rb_str_new(NULL, ASN1_STRING_length(name_hash) * 2);
+    ossl_bin2hex(ASN1_STRING_get0_data(name_hash), RSTRING_PTR(ret),
+                 ASN1_STRING_length(name_hash));
 
     return ret;
 }
@@ -1573,8 +1574,9 @@ ossl_ocspcid_get_issuer_key_hash(VALUE self)
     GetOCSPCertId(self, id);
     OCSP_id_get0_info(NULL, NULL, &key_hash, NULL, id);
 
-    ret = rb_str_new(NULL, key_hash->length * 2);
-    ossl_bin2hex(key_hash->data, RSTRING_PTR(ret), key_hash->length);
+    ret = rb_str_new(NULL, ASN1_STRING_length(key_hash) * 2);
+    ossl_bin2hex(ASN1_STRING_get0_data(key_hash), RSTRING_PTR(ret),
+                 ASN1_STRING_length(key_hash));
 
     return ret;
 }
diff --git a/ext/openssl/ossl_ts.c b/ext/openssl/ossl_ts.c
index 615eedc016a0f4..b31a854a63e9ac 100644
--- a/ext/openssl/ossl_ts.c
+++ b/ext/openssl/ossl_ts.c
@@ -259,7 +259,7 @@ ossl_ts_req_get_msg_imprint(VALUE self)
     mi = TS_REQ_get_msg_imprint(req);
     hashed_msg = TS_MSG_IMPRINT_get_msg(mi);
 
-    ret = rb_str_new((const char *)hashed_msg->data, hashed_msg->length);
+    ret = asn1str_to_str(hashed_msg);
 
     return ret;
 }
@@ -470,7 +470,7 @@ ossl_ts_req_to_der(VALUE self)
         ossl_raise(eTimestampError, "Message imprint missing algorithm");
 
     hashed_msg = TS_MSG_IMPRINT_get_msg(mi);
-    if (!hashed_msg->length)
+    if (!ASN1_STRING_length(hashed_msg))
         ossl_raise(eTimestampError, "Message imprint missing hashed message");
 
     return asn1_to_der((void *)req, (int (*)(void *, unsigned char **))i2d_TS_REQ);
@@ -981,7 +981,7 @@ ossl_ts_token_info_get_msg_imprint(VALUE self)
     GetTSTokenInfo(self, info);
     mi = TS_TST_INFO_get_msg_imprint(info);
     hashed_msg = TS_MSG_IMPRINT_get_msg(mi);
-    ret = rb_str_new((const char *)hashed_msg->data, hashed_msg->length);
+    ret = asn1str_to_str(hashed_msg);
 
     return ret;
 }
diff --git a/ext/openssl/ossl_x509ext.c b/ext/openssl/ossl_x509ext.c
index 85e2eff7a275c6..ef66ecc3fe8390 100644
--- a/ext/openssl/ossl_x509ext.c
+++ b/ext/openssl/ossl_x509ext.c
@@ -402,7 +402,7 @@ ossl_x509ext_get_value_der(VALUE obj)
     if ((value = X509_EXTENSION_get_data(ext)) == NULL)
         ossl_raise(eX509ExtError, NULL);
 
-    return rb_str_new((const char *)value->data, value->length);
+    return asn1str_to_str(value);
 }
 
 static VALUE
diff --git a/ext/stringio/stringio.c b/ext/stringio/stringio.c
index 5556426fdc387a..9240929646d5ea 100644
--- a/ext/stringio/stringio.c
+++ b/ext/stringio/stringio.c
@@ -1888,7 +1888,7 @@ strio_truncate(VALUE self, VALUE len)
  *   external_encoding -> encoding or nil
  *
  * Returns an Encoding object that represents the encoding of the string;
- * see {Encoding}[rdoc-ref:Encoding]:
+ * see {Encodings}[rdoc-ref:StringIO@Encodings]:
  *
  *   strio = StringIO.new('foo')
  *   strio.external_encoding # => #<Encoding:UTF-8>
diff --git a/gc.c b/gc.c
index 4f5f041fb348fb..c660d1491f3a6d 100644
--- a/gc.c
+++ b/gc.c
@@ -1905,7 +1905,9 @@ object_id0(VALUE obj)
     RUBY_ASSERT(rb_shape_obj_has_id(obj));
 
     if (RB_UNLIKELY(id2ref_tbl)) {
-        st_insert(id2ref_tbl, (st_data_t)id, (st_data_t)obj);
+        RB_VM_LOCKING() {
+            st_insert(id2ref_tbl, (st_data_t)id, (st_data_t)obj);
+        }
     }
     return id;
 }
diff --git a/io_buffer.c b/io_buffer.c
index 0d2cbdb4b7e704..b81527ff71147a 100644
--- a/io_buffer.c
+++ b/io_buffer.c
@@ -1928,13 +1928,19 @@ ruby_swap128_uint(rb_uint128_t x)
     return result;
 }
 
+union uint128_int128_conversion {
+    rb_uint128_t uint128;
+    rb_int128_t int128;
+};
+
 static inline rb_int128_t
 ruby_swap128_int(rb_int128_t x)
 {
-    // Cast to unsigned, swap, then cast back
-    rb_uint128_t u = *(rb_uint128_t*)&x;
-    rb_uint128_t swapped = ruby_swap128_uint(u);
-    return *(rb_int128_t*)&swapped;
+    union uint128_int128_conversion conversion = {
+        .int128 = x
+    };
+    conversion.uint128 = ruby_swap128_uint(conversion.uint128);
+    return conversion.int128;
 }
 
 #define IO_BUFFER_DECLARE_TYPE(name, type, endian, wrap, unwrap, swap) \
diff --git a/pathname_builtin.rb b/pathname_builtin.rb
index 1dedf5e08df546..3d78619c9e4041 100644
--- a/pathname_builtin.rb
+++ b/pathname_builtin.rb
@@ -195,15 +195,14 @@ class Pathname
 
   # :stopdoc:
 
-  # to_path is implemented so Pathname objects are usable with File.open, etc.
-  TO_PATH = :to_path
-
   SAME_PATHS = if File::FNM_SYSCASE.nonzero?
     # Avoid #zero? here because #casecmp can return nil.
     proc {|a, b| a.casecmp(b) == 0}
   else
     proc {|a, b| a == b}
   end
+  SAME_PATHS.freeze
+  private_constant :SAME_PATHS
 
   attr_reader :path
   protected :path
@@ -215,17 +214,7 @@ class Pathname
   # If +path+ contains a NUL character (<tt>\0</tt>), an ArgumentError is raised.
   #
   def initialize(path)
-    unless String === path
-      path = path.to_path if path.respond_to? :to_path
-      path = path.to_str if path.respond_to? :to_str
-      raise TypeError, "Pathname.new requires a String, #to_path or #to_str" unless String === path
-    end
-
-    if path.include?("\0")
-      raise ArgumentError, "pathname contains \\0: #{path.inspect}"
-    end
-
-    @path = path.dup
+    @path = File.path(path).dup
   end
 
   def freeze
@@ -264,7 +253,7 @@ def to_s
   end
 
   # to_path is implemented so Pathname objects are usable with File.open, etc.
-  alias_method TO_PATH, :to_s
+  alias to_path to_s
 
   def inspect # :nodoc:
     "#<#{self.class}:#{@path}>"
@@ -320,6 +309,9 @@ def sub_ext(repl)
     SEPARATOR_LIST = Regexp.quote File::SEPARATOR
     SEPARATOR_PAT = /#{SEPARATOR_LIST}/
   end
+  SEPARATOR_LIST.freeze
+  SEPARATOR_PAT.freeze
+  private_constant :SEPARATOR_LIST, :SEPARATOR_LIST
 
   if File.dirname('A:') == 'A:.' # DOSish drive letter
     # Regexp that matches an absolute path.
@@ -327,6 +319,7 @@ def sub_ext(repl)
   else
     ABSOLUTE_PATH = /\A#{SEPARATOR_PAT}/
   end
+  ABSOLUTE_PATH.freeze
   private_constant :ABSOLUTE_PATH
 
   # :startdoc:
diff --git a/test/-ext-/scheduler/test_interrupt_with_scheduler.rb b/test/-ext-/scheduler/test_interrupt_with_scheduler.rb
index 3f9a7f55a07d11..42a109b98b51a6 100644
--- a/test/-ext-/scheduler/test_interrupt_with_scheduler.rb
+++ b/test/-ext-/scheduler/test_interrupt_with_scheduler.rb
@@ -13,6 +13,8 @@ def setup
   def test_without_handle_interrupt_signal_works
     IO.pipe do |input, output|
       pid = fork do
+        STDERR.reopen(output)
+
         scheduler = Scheduler.new
         Fiber.set_scheduler scheduler
 
@@ -33,7 +35,7 @@ def test_without_handle_interrupt_signal_works
       assert_equal "ready\n", input.gets
 
       sleep 0.1 # Ensure the child is in the blocking loop
-      $stderr.puts "Sending interrupt"
+      # $stderr.puts "Sending interrupt"
       Process.kill(:INT, pid)
 
       reaper = Thread.new do