diff --git a/ChangeLog.d/8726.txt b/ChangeLog.d/8726.txt
new file mode 100644
index 0000000..c1e5a40
--- /dev/null
+++ b/ChangeLog.d/8726.txt
@@ -0,0 +1,2 @@
+Features
+   * Add partial platform support for z/OS.
diff --git a/ChangeLog.d/iar-gcc-perf.txt b/ChangeLog.d/iar-gcc-perf.txt
new file mode 100644
index 0000000..fb0fbb1
--- /dev/null
+++ b/ChangeLog.d/iar-gcc-perf.txt
@@ -0,0 +1,2 @@
+Features
+   * Improve performance for gcc (versions older than 9.3.0) and IAR.
diff --git a/include/mbedtls/build_info.h b/include/mbedtls/build_info.h
index b2ab104..2f336ba 100644
--- a/include/mbedtls/build_info.h
+++ b/include/mbedtls/build_info.h
@@ -83,6 +83,14 @@
 #endif
 #endif
 
+#if defined(__GNUC__) && !defined(__ARMCC_VERSION) && !defined(__clang__) \
+    && !defined(__llvm__) && !defined(__INTEL_COMPILER)
+/* Defined if the compiler really is gcc and not clang, etc */
+#define MBEDTLS_COMPILER_IS_GCC
+#define MBEDTLS_GCC_VERSION \
+    (__GNUC__ * 10000 + __GNUC_MINOR__ * 100 + __GNUC_PATCHLEVEL__)
+#endif
+
 #if defined(_MSC_VER) && !defined(_CRT_SECURE_NO_DEPRECATE)
 #define _CRT_SECURE_NO_DEPRECATE 1
 #endif
diff --git a/library/alignment.h b/library/alignment.h
index 9e1e044..248f29b 100644
--- a/library/alignment.h
+++ b/library/alignment.h
@@ -37,6 +37,52 @@
 #define MBEDTLS_EFFICIENT_UNALIGNED_ACCESS
 #endif
 
+#if defined(__IAR_SYSTEMS_ICC__) && \
+    (defined(MBEDTLS_ARCH_IS_ARM64) || defined(MBEDTLS_ARCH_IS_ARM32) \
+    || defined(__ICCRX__) || defined(__ICCRL78__) || defined(__ICCRISCV__))
+#pragma language=save
+#pragma language=extended
+#define MBEDTLS_POP_IAR_LANGUAGE_PRAGMA
+/* IAR recommend this technique for accessing unaligned data in
+ * https://www.iar.com/knowledge/support/technical-notes/compiler/accessing-unaligned-data
+ * This results in a single load / store instruction (if unaligned access is supported).
+ * According to that document, this is only supported on certain architectures.
+ */
+    #define UINT_UNALIGNED
+typedef uint16_t __packed mbedtls_uint16_unaligned_t;
+typedef uint32_t __packed mbedtls_uint32_unaligned_t;
+typedef uint64_t __packed mbedtls_uint64_unaligned_t;
+#elif defined(MBEDTLS_COMPILER_IS_GCC) && (MBEDTLS_GCC_VERSION >= 40504) && \
+    ((MBEDTLS_GCC_VERSION < 90300) || (!defined(MBEDTLS_EFFICIENT_UNALIGNED_ACCESS)))
+/*
+ * Old versions of gcc, depending on how the target is specified, may generate a branch to memcpy
+ * for calls like `memcpy(dest, src, 4)` rather than generating some LDR or LDRB instructions
+ * (similar for stores).
+ * Recent versions where unaligned access is not enabled also do this.
+ *
+ * For performance (and code size, in some cases), we want to avoid the branch and just generate
+ * some inline load/store instructions since the access is small and constant-size.
+ *
+ * The manual states:
+ * "The aligned attribute specifies a minimum alignment for the variable or structure field,
+ * measured in bytes."
+ * https://gcc.gnu.org/onlinedocs/gcc/Common-Variable-Attributes.html
+ *
+ * Tested with several versions of GCC from 4.5.0 up to 9.3.0
+ * We don't enable for older than 4.5.0 as this has not been tested.
+ */
+ #define UINT_UNALIGNED
+typedef uint16_t __attribute__((__aligned__(1))) mbedtls_uint16_unaligned_t;
+typedef uint32_t __attribute__((__aligned__(1))) mbedtls_uint32_unaligned_t;
+typedef uint64_t __attribute__((__aligned__(1))) mbedtls_uint64_unaligned_t;
+ #endif
+
+/*
+ * We try to force mbedtls_(get|put)_unaligned_uintXX to be always inline, because this results
+ * in code that is both smaller and faster. IAR and gcc both benefit from this when optimising
+ * for size.
+ */
+
 /**
  * Read the unsigned 16 bits integer from the given address, which need not
  * be aligned.
@@ -44,10 +90,20 @@
  * \param   p pointer to 2 bytes of data
  * \return  Data at the given address
  */
-inline uint16_t mbedtls_get_unaligned_uint16(const void *p)
+#if defined(__IAR_SYSTEMS_ICC__)
+#pragma inline = forced
+#elif defined(__GNUC__)
+__attribute__((always_inline))
+#endif
+static inline uint16_t mbedtls_get_unaligned_uint16(const void *p)
 {
     uint16_t r;
+#if defined(UINT_UNALIGNED)
+    mbedtls_uint16_unaligned_t *p16 = (mbedtls_uint16_unaligned_t *) p;
+    r = *p16;
+#else
     memcpy(&r, p, sizeof(r));
+#endif
     return r;
 }
 
@@ -58,9 +114,19 @@
  * \param   p pointer to 2 bytes of data
  * \param   x data to write
  */
-inline void mbedtls_put_unaligned_uint16(void *p, uint16_t x)
+#if defined(__IAR_SYSTEMS_ICC__)
+#pragma inline = forced
+#elif defined(__GNUC__)
+__attribute__((always_inline))
+#endif
+static inline void mbedtls_put_unaligned_uint16(void *p, uint16_t x)
 {
+#if defined(UINT_UNALIGNED)
+    mbedtls_uint16_unaligned_t *p16 = (mbedtls_uint16_unaligned_t *) p;
+    *p16 = x;
+#else
     memcpy(p, &x, sizeof(x));
+#endif
 }
 
 /**
@@ -70,10 +136,20 @@
  * \param   p pointer to 4 bytes of data
  * \return  Data at the given address
  */
-inline uint32_t mbedtls_get_unaligned_uint32(const void *p)
+#if defined(__IAR_SYSTEMS_ICC__)
+#pragma inline = forced
+#elif defined(__GNUC__)
+__attribute__((always_inline))
+#endif
+static inline uint32_t mbedtls_get_unaligned_uint32(const void *p)
 {
     uint32_t r;
+#if defined(UINT_UNALIGNED)
+    mbedtls_uint32_unaligned_t *p32 = (mbedtls_uint32_unaligned_t *) p;
+    r = *p32;
+#else
     memcpy(&r, p, sizeof(r));
+#endif
     return r;
 }
 
@@ -84,9 +160,19 @@
  * \param   p pointer to 4 bytes of data
  * \param   x data to write
  */
-inline void mbedtls_put_unaligned_uint32(void *p, uint32_t x)
+#if defined(__IAR_SYSTEMS_ICC__)
+#pragma inline = forced
+#elif defined(__GNUC__)
+__attribute__((always_inline))
+#endif
+static inline void mbedtls_put_unaligned_uint32(void *p, uint32_t x)
 {
+#if defined(UINT_UNALIGNED)
+    mbedtls_uint32_unaligned_t *p32 = (mbedtls_uint32_unaligned_t *) p;
+    *p32 = x;
+#else
     memcpy(p, &x, sizeof(x));
+#endif
 }
 
 /**
@@ -96,10 +182,20 @@
  * \param   p pointer to 8 bytes of data
  * \return  Data at the given address
  */
-inline uint64_t mbedtls_get_unaligned_uint64(const void *p)
+#if defined(__IAR_SYSTEMS_ICC__)
+#pragma inline = forced
+#elif defined(__GNUC__)
+__attribute__((always_inline))
+#endif
+static inline uint64_t mbedtls_get_unaligned_uint64(const void *p)
 {
     uint64_t r;
+#if defined(UINT_UNALIGNED)
+    mbedtls_uint64_unaligned_t *p64 = (mbedtls_uint64_unaligned_t *) p;
+    r = *p64;
+#else
     memcpy(&r, p, sizeof(r));
+#endif
     return r;
 }
 
@@ -110,11 +206,25 @@
  * \param   p pointer to 8 bytes of data
  * \param   x data to write
  */
-inline void mbedtls_put_unaligned_uint64(void *p, uint64_t x)
+#if defined(__IAR_SYSTEMS_ICC__)
+#pragma inline = forced
+#elif defined(__GNUC__)
+__attribute__((always_inline))
+#endif
+static inline void mbedtls_put_unaligned_uint64(void *p, uint64_t x)
 {
+#if defined(UINT_UNALIGNED)
+    mbedtls_uint64_unaligned_t *p64 = (mbedtls_uint64_unaligned_t *) p;
+    *p64 = x;
+#else
     memcpy(p, &x, sizeof(x));
+#endif
 }
 
+#if defined(MBEDTLS_POP_IAR_LANGUAGE_PRAGMA)
+#pragma language=restore
+#endif
+
 /** Byte Reading Macros
  *
  * Given a multi-byte integer \p x, MBEDTLS_BYTE_n retrieves the n-th
diff --git a/library/common.h b/library/common.h
index e532777..3936ffd 100644
--- a/library/common.h
+++ b/library/common.h
@@ -27,15 +27,6 @@
 #define MBEDTLS_HAVE_NEON_INTRINSICS
 #endif
 
-
-#if defined(__GNUC__) && !defined(__ARMCC_VERSION) && !defined(__clang__) \
-    && !defined(__llvm__) && !defined(__INTEL_COMPILER)
-/* Defined if the compiler really is gcc and not clang, etc */
-#define MBEDTLS_COMPILER_IS_GCC
-#define MBEDTLS_GCC_VERSION \
-    (__GNUC__ * 10000 + __GNUC_MINOR__ * 100 + __GNUC_PATCHLEVEL__)
-#endif
-
 /** Helper to define a function as static except when building invasive tests.
  *
  * If a function is only used inside its own source file and should be
@@ -167,6 +158,12 @@
     return p == NULL ? NULL : p + n;
 }
 
+/* Always inline mbedtls_xor() for similar reasons as mbedtls_xor_no_simd(). */
+#if defined(__IAR_SYSTEMS_ICC__)
+#pragma inline = forced
+#elif defined(__GNUC__)
+__attribute__((always_inline))
+#endif
 /**
  * Perform a fast block XOR operation, such that
  * r[i] = a[i] ^ b[i] where 0 <= i < n
@@ -177,8 +174,19 @@
  * \param   a Pointer to input (buffer of at least \p n bytes)
  * \param   b Pointer to input (buffer of at least \p n bytes)
  * \param   n Number of bytes to process.
+ *
+ * \note      Depending on the situation, it may be faster to use either mbedtls_xor() or
+ *            mbedtls_xor_no_simd() (these are functionally equivalent).
+ *            If the result is used immediately after the xor operation in non-SIMD code (e.g, in
+ *            AES-CBC), there may be additional latency to transfer the data from SIMD to scalar
+ *            registers, and in this case, mbedtls_xor_no_simd() may be faster. In other cases where
+ *            the result is not used immediately (e.g., in AES-CTR), mbedtls_xor() may be faster.
+ *            For targets without SIMD support, they will behave the same.
  */
-inline void mbedtls_xor(unsigned char *r, const unsigned char *a, const unsigned char *b, size_t n)
+static inline void mbedtls_xor(unsigned char *r,
+                               const unsigned char *a,
+                               const unsigned char *b,
+                               size_t n)
 {
     size_t i = 0;
 #if defined(MBEDTLS_EFFICIENT_UNALIGNED_ACCESS)
@@ -191,17 +199,36 @@
         uint8x16_t x = veorq_u8(v1, v2);
         vst1q_u8(r + i, x);
     }
+#if defined(__IAR_SYSTEMS_ICC__)
+    /* This if statement helps some compilers (e.g., IAR) optimise out the byte-by-byte tail case
+     * where n is a constant multiple of 16.
+     * For other compilers (e.g. recent gcc and clang) it makes no difference if n is a compile-time
+     * constant, and is a very small perf regression if n is not a compile-time constant. */
+    if (n % 16 == 0) {
+        return;
+    }
+#endif
 #elif defined(MBEDTLS_ARCH_IS_X64) || defined(MBEDTLS_ARCH_IS_ARM64)
     /* This codepath probably only makes sense on architectures with 64-bit registers */
     for (; (i + 8) <= n; i += 8) {
         uint64_t x = mbedtls_get_unaligned_uint64(a + i) ^ mbedtls_get_unaligned_uint64(b + i);
         mbedtls_put_unaligned_uint64(r + i, x);
     }
+#if defined(__IAR_SYSTEMS_ICC__)
+    if (n % 8 == 0) {
+        return;
+    }
+#endif
 #else
     for (; (i + 4) <= n; i += 4) {
         uint32_t x = mbedtls_get_unaligned_uint32(a + i) ^ mbedtls_get_unaligned_uint32(b + i);
         mbedtls_put_unaligned_uint32(r + i, x);
     }
+#if defined(__IAR_SYSTEMS_ICC__)
+    if (n % 4 == 0) {
+        return;
+    }
+#endif
 #endif
 #endif
     for (; i < n; i++) {
@@ -209,11 +236,18 @@
     }
 }
 
+/* Always inline mbedtls_xor_no_simd() as we see significant perf regressions when it does not get
+ * inlined (e.g., observed about 3x perf difference in gcm_mult_largetable with gcc 7 - 12) */
+#if defined(__IAR_SYSTEMS_ICC__)
+#pragma inline = forced
+#elif defined(__GNUC__)
+__attribute__((always_inline))
+#endif
 /**
  * Perform a fast block XOR operation, such that
  * r[i] = a[i] ^ b[i] where 0 <= i < n
  *
- * In some situations, this can perform better than mbedtls_xor (e.g., it's about 5%
+ * In some situations, this can perform better than mbedtls_xor() (e.g., it's about 5%
  * better in AES-CBC).
  *
  * \param   r Pointer to result (buffer of at least \p n bytes). \p r
@@ -222,6 +256,14 @@
  * \param   a Pointer to input (buffer of at least \p n bytes)
  * \param   b Pointer to input (buffer of at least \p n bytes)
  * \param   n Number of bytes to process.
+ *
+ * \note      Depending on the situation, it may be faster to use either mbedtls_xor() or
+ *            mbedtls_xor_no_simd() (these are functionally equivalent).
+ *            If the result is used immediately after the xor operation in non-SIMD code (e.g, in
+ *            AES-CBC), there may be additional latency to transfer the data from SIMD to scalar
+ *            registers, and in this case, mbedtls_xor_no_simd() may be faster. In other cases where
+ *            the result is not used immediately (e.g., in AES-CTR), mbedtls_xor() may be faster.
+ *            For targets without SIMD support, they will behave the same.
  */
 static inline void mbedtls_xor_no_simd(unsigned char *r,
                                        const unsigned char *a,
@@ -236,11 +278,25 @@
         uint64_t x = mbedtls_get_unaligned_uint64(a + i) ^ mbedtls_get_unaligned_uint64(b + i);
         mbedtls_put_unaligned_uint64(r + i, x);
     }
+#if defined(__IAR_SYSTEMS_ICC__)
+    /* This if statement helps some compilers (e.g., IAR) optimise out the byte-by-byte tail case
+     * where n is a constant multiple of 8.
+     * For other compilers (e.g. recent gcc and clang) it makes no difference if n is a compile-time
+     * constant, and is a very small perf regression if n is not a compile-time constant. */
+    if (n % 8 == 0) {
+        return;
+    }
+#endif
 #else
     for (; (i + 4) <= n; i += 4) {
         uint32_t x = mbedtls_get_unaligned_uint32(a + i) ^ mbedtls_get_unaligned_uint32(b + i);
         mbedtls_put_unaligned_uint32(r + i, x);
     }
+#if defined(__IAR_SYSTEMS_ICC__)
+    if (n % 4 == 0) {
+        return;
+    }
+#endif
 #endif
 #endif
     for (; i < n; i++) {
diff --git a/library/entropy_poll.c b/library/entropy_poll.c
index de2e038..bd21e2d 100644
--- a/library/entropy_poll.c
+++ b/library/entropy_poll.c
@@ -29,7 +29,7 @@
 
 #if !defined(unix) && !defined(__unix__) && !defined(__unix) && \
     !defined(__APPLE__) && !defined(_WIN32) && !defined(__QNXNTO__) && \
-    !defined(__HAIKU__) && !defined(__midipix__)
+    !defined(__HAIKU__) && !defined(__midipix__) && !defined(__MVS__)
 #error \
     "Platform entropy sources only work on Unix and Windows, see MBEDTLS_NO_PLATFORM_ENTROPY in mbedtls_config.h"
 #endif
diff --git a/library/platform_util.c b/library/platform_util.c
index 63643d2..9f5dcb8 100644
--- a/library/platform_util.c
+++ b/library/platform_util.c
@@ -217,27 +217,6 @@
 void (*mbedtls_test_hook_test_fail)(const char *, int, const char *);
 #endif /* MBEDTLS_TEST_HOOKS */
 
-/*
- * Provide external definitions of some inline functions so that the compiler
- * has the option to not inline them
- */
-extern inline void mbedtls_xor(unsigned char *r,
-                               const unsigned char *a,
-                               const unsigned char *b,
-                               size_t n);
-
-extern inline uint16_t mbedtls_get_unaligned_uint16(const void *p);
-
-extern inline void mbedtls_put_unaligned_uint16(void *p, uint16_t x);
-
-extern inline uint32_t mbedtls_get_unaligned_uint32(const void *p);
-
-extern inline void mbedtls_put_unaligned_uint32(void *p, uint32_t x);
-
-extern inline uint64_t mbedtls_get_unaligned_uint64(const void *p);
-
-extern inline void mbedtls_put_unaligned_uint64(void *p, uint64_t x);
-
 #if defined(MBEDTLS_HAVE_TIME) && !defined(MBEDTLS_PLATFORM_MS_TIME_ALT)
 
 #include <time.h>