libc/minimal: Add rand and srand

doc/guides/portability/posix.rst

@@ -282,7 +282,7 @@ This is implemented as part of the minimal C library available in Zephyr.
     setlocale(),
     snprintf(),+
     sprintf(),+
-    srand(),
+    srand(),+
     sscanf(),
     strcat(),+
     strchr(),+

doc/guides/porting/arch.rst

@@ -795,7 +795,7 @@ details:
 
 Some architectures may need to update software memory management structures
 or modify hardware registers on another CPU when memory domain APIs are invoked.
-If so, CONFIG_ARCH_MEM_DOMAIN_SYNCHRONOUS_API must be selected by the
+If so, :kconfig:`CONFIG_ARCH_MEM_DOMAIN_SYNCHRONOUS_API` must be selected by the
 architecture and some additional APIs must be implemented. This is common
 on MMU systems and uncommon on MPU systems:
 

doc/reference/kernel/other/interrupts.rst

@@ -377,10 +377,10 @@ argument is ignored.
 
 Vector Table
 ------------
-A vector table is generated when CONFIG_GEN_IRQ_VECTOR_TABLE is enabled.  This
-data structure is used natively by the CPU and is simply an array of function
-pointers, where each element n corresponds to the IRQ handler for IRQ line n,
-and the function pointers are:
+A vector table is generated when :kconfig:`CONFIG_GEN_IRQ_VECTOR_TABLE` is
+enabled.  This data structure is used natively by the CPU and is simply an
+array of function pointers, where each element n corresponds to the IRQ handler
+for IRQ line n, and the function pointers are:
 
 #. For 'direct' interrupts declared with :c:macro:`IRQ_DIRECT_CONNECT`, the
    handler function will be placed here.
@@ -394,7 +394,8 @@ and the function pointers are:
 
 Some architectures (such as the Nios II internal interrupt controller) have a
 common entry point for all interrupts and do not support a vector table, in
-which case the CONFIG_GEN_IRQ_VECTOR_TABLE option should be disabled.
+which case the :kconfig:`CONFIG_GEN_IRQ_VECTOR_TABLE` option should be
+disabled.
 
 Some architectures may reserve some initial vectors for system exceptions
 and declare this in a table elsewhere, in which case

doc/reference/kernel/threads/index.rst

@@ -485,8 +485,8 @@ The following code illustrates the ways a thread can terminate.
         /* thread terminates at end of entry point function */
     }
 
-If CONFIG_USERSPACE is enabled, aborting a thread will additionally mark the
-thread and stack objects as uninitialized so that they may be re-used.
+If :kconfig:`CONFIG_USERSPACE` is enabled, aborting a thread will additionally
+mark the thread and stack objects as uninitialized so that they may be re-used.
 
 Runtime Statistics
 ******************

doc/reference/usermode/memory_domain.rst

@@ -49,7 +49,8 @@ Hardware Stack Overflow
 ``CONFIG_HW_STACK_PROTECTION`` is an optional feature which detects stack
 buffer overflows when the system is running in supervisor mode. This
 catches issues when the entire stack buffer has overflowed, and not
-individual stack frames, use compiler-assisted CONFIG_STACK_CANARIES for that.
+individual stack frames, use compiler-assisted :kconfig:`CONFIG_STACK_CANARIES`
+for that.
 
 Like any crash in supervisor mode, no guarantees can be made about the overall
 health of the system after a supervisor mode stack overflow, and any instances
@@ -199,7 +200,7 @@ automatically.
 Manual Memory Partitions
 ------------------------
 
-The following code declares a global array buf, and then declares
+The following code declares a global array ``buf``, and then declares
 a read-write partition for it which may be added to a domain:
 
 .. code-block:: c
@@ -254,7 +255,7 @@ BSS.
      */
     K_APP_BMEM(my_partition) int var2;
 
-The build system will ensure that the base address of my_partition will
+The build system will ensure that the base address of ``my_partition`` will
 be properly aligned, and the total size of the region conforms to the memory
 management hardware requirements, adding padding if necessary.
 
@@ -301,8 +302,8 @@ There are a few memory partitions which are pre-defined by the system:
    to specific memory domains.
 
  - ``z_libc_partition`` - Contains globals required by the C library and runtime.
-   Required if using newlib. Required if using minimal libc with
-   ``CONFIG_STACK_CANARIES`` enabled.
+   Required when using either the Minimal C library or the Newlib C Library.
+   Required when option:`CONFIG_STACK_CANARIES` is enabled.
 
 Library-specific partitions are listed in ``include/app_memory/partitions.h``.
 For example, to use the MBEDTLS library from user mode, the

include/sys/libc-hooks.h

@@ -69,11 +69,14 @@ extern struct k_mem_partition z_malloc_partition;
 
 #if defined(CONFIG_NEWLIB_LIBC) || defined(CONFIG_STACK_CANARIES) || \
     defined(CONFIG_NEED_LIBC_MEM_PARTITION)
-/* Minimal libc has no globals. We do put the stack canary global in the
- * libc partition since it is not worth placing in a partition of its own.
- *
- * Some architectures require a global pointer for thread local storage,
- * which is placed inside the libc partition.
+/* - All newlib globals will be placed into z_libc_partition.
+ * - Minimal C library globals, if any, will be placed into
+ *   z_libc_partition.
+ * - Stack canary globals will be placed into z_libc_partition since
+ *   it is not worth placing in its own partition.
+ * - Some architectures may place the global pointer to the thread local
+ *   storage in z_libc_partition since it is not worth placing in its
+ *   own partition.
  */
 #define Z_LIBC_PARTITION_EXISTS 1
 

lib/libc/Kconfig

@@ -145,6 +145,19 @@ config MINIMAL_LIBC_OPTIMIZE_STRING_FOR_SIZE
 	  Enable smaller but potentially slower implementations of memcpy and
 	  memset. On the Cortex-M0+ this reduces the total code size by 120 bytes.
 
+config MINIMAL_LIBC_RAND
+	bool "Enables rand and srand functions"
+	select NEED_LIBC_MEM_PARTITION
+	help
+	  Enable rand() and srand() for the minimal libc. The
+	  functions implicitly access global/static data.  Such data
+	  must be put into a memory partition if CONFIG_USERSPACE=y,
+	  and disabling this option may save an entry for application
+	  defining many custom partitions.
+
+	  Say 'Y' here if you need rand() and srand(). This might require
+	  an additional memory partition.
+
 endif # MINIMAL_LIBC
 
 config STDOUT_CONSOLE

lib/libc/minimal/CMakeLists.txt

@@ -22,3 +22,4 @@ zephyr_library_sources(
 )
 
 zephyr_library_sources_ifdef(CONFIG_POSIX_CLOCK source/time/time.c)
+zephyr_library_sources_ifdef(CONFIG_MINIMAL_LIBC_RAND source/stdlib/rand.c)

lib/libc/minimal/include/stdlib.h

@@ -10,6 +10,8 @@
 #define ZEPHYR_LIB_LIBC_MINIMAL_INCLUDE_STDLIB_H_
 
 #include <stddef.h>
+#include <limits.h>
+
 #ifdef __cplusplus
 extern "C" {
 #endif
@@ -37,7 +39,11 @@ static inline void exit(int status)
 }
 void abort(void);
 
+#ifdef CONFIG_MINIMAL_LIBC_RAND
+#define RAND_MAX INT_MAX
 int rand(void);
+void srand(unsigned int seed);
+#endif /* CONFIG_MINIMAL_LIBC_RAND */
 
 static inline int abs(int __n)
 {

lib/libc/minimal/source/stdlib/rand.c

@@ -0,0 +1,29 @@
+/*
+ * Copyright (c) 2021 Space Cubics, LLC.
+ *
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+#include <stdlib.h>
+#include <sys/libc-hooks.h>
+#include <app_memory/app_memdomain.h>
+
+#define LIBC_DATA K_APP_DMEM(z_libc_partition)
+
+#define OUTPUT_BITS (0x7fffffffU)
+#define MULTIPLIER (1103515245U)
+#define INCREMENT (12345U)
+
+static LIBC_DATA unsigned long srand_seed = 1;
+
+void srand(unsigned int s)
+{
+	srand_seed = s;
+}
+
+int rand(void)
+{
+	srand_seed = (MULTIPLIER * srand_seed + INCREMENT) & OUTPUT_BITS;
+
+	return srand_seed;
+}

tests/crypto/mbedtls/prj.conf

@@ -5,3 +5,4 @@ CONFIG_MBEDTLS_CFG_FILE="config-tls-generic.h"
 CONFIG_MBEDTLS_TEST=y
 CONFIG_ZTEST=y
 CONFIG_TEST_USERSPACE=y
+CONFIG_MINIMAL_LIBC_RAND=y

tests/crypto/mbedtls/src/mbedtls.c

@@ -72,20 +72,6 @@
 #include "mbedtls/memory_buffer_alloc.h"
 #endif
 
-#if defined(MBEDTLS_RSA_C)
-int rand(void)
-{
-	static ZTEST_DMEM uint32_t seed = 7U;
-
-	seed ^= seed << 13;
-	seed ^= seed >> 17;
-	seed ^= seed << 5;
-
-	return seed;
-}
-
-#endif
-
 static int test_snprintf(size_t n, const char ref_buf[10], int ref_ret)
 {
 	int ret;

tests/lib/c_lib/prj.conf

@@ -1,3 +1,4 @@
 CONFIG_ZTEST=y
 CONFIG_TEST_USERSPACE=y
 CONFIG_ZTEST_FATAL_HOOK=y
+CONFIG_MINIMAL_LIBC_RAND=y

tests/lib/c_lib/src/main.c

@@ -899,6 +899,112 @@ void test_time(void)
 	zassert_not_null(gmtime_r(&tests4, &tp), "gmtime_r failed");
 }
 
+/**
+ *
+ * @brief Test rand function
+ *
+ */
+void test_rand(void)
+{
+	int a;
+
+	a = rand();
+	/* The default seed is 1 */
+	zassert_equal(a, 1103527590, "rand failed");
+}
+
+/**
+ *
+ * @brief Test srand function
+ *
+ */
+void test_srand(void)
+{
+	int a;
+
+	srand(0);
+	a = rand();
+	zassert_equal(a, 12345, "srand with seed 0 failed");
+
+	srand(1);
+	a = rand();
+	zassert_equal(a, 1103527590, "srand with seed 1 failed");
+
+	srand(10);
+	a = rand();
+	zassert_equal(a, 297746555, "srand with seed 10 failed");
+
+	srand(UINT_MAX - 1);
+	a = rand();
+	zassert_equal(a, 2087949151, "srand with seed UINT_MAX - 1 failed");
+
+	srand(UINT_MAX);
+	a = rand();
+	zassert_equal(a, 1043980748, "srand with seed UINT_MAX failed");
+}
+
+/**
+ *
+ * @brief Test rand function for reproducibility
+ *
+ */
+void test_rand_reproducibility(void)
+{
+	int a;
+	int b;
+	int c;
+
+	srand(0);
+	a = rand();
+	zassert_equal(a, 12345, "srand with seed 0 failed");
+	srand(0);
+	b = rand();
+	zassert_equal(b, 12345, "srand with seed 0 failed (2nd)");
+	srand(0);
+	c = rand();
+	zassert_equal(c, 12345, "srand with seed 0 failed (3rd)");
+
+	srand(1);
+	a = rand();
+	zassert_equal(a, 1103527590, "srand with seed 1 failed");
+	srand(1);
+	b = rand();
+	zassert_equal(b, 1103527590, "srand with seed 1 failed (2nd)");
+	srand(1);
+	c = rand();
+	zassert_equal(c, 1103527590, "srand with seed 1 failed (3rd)");
+
+	srand(10);
+	a = rand();
+	zassert_equal(a, 297746555, "srand with seed 10 failed");
+	srand(10);
+	b = rand();
+	zassert_equal(b, 297746555, "srand with seed 10 failed (2nd)");
+	srand(10);
+	c = rand();
+	zassert_equal(c, 297746555, "srand with seed 10 failed (3rd)");
+
+	srand(UINT_MAX - 1);
+	a = rand();
+	zassert_equal(a, 2087949151, "srand with seed UINT_MAX - 1 failed");
+	srand(UINT_MAX - 1);
+	b = rand();
+	zassert_equal(b, 2087949151, "srand with seed UINT_MAX - 1 failed (2nd)");
+	srand(UINT_MAX - 1);
+	c = rand();
+	zassert_equal(c, 2087949151, "srand with seed UINT_MAX - 1 failed (3rd)");
+
+	srand(UINT_MAX);
+	a = rand();
+	zassert_equal(a, 1043980748, "srand with seed UINT_MAX failed");
+	srand(UINT_MAX);
+	b = rand();
+	zassert_equal(b, 1043980748, "srand with seed UINT_MAX failed (2nd)");
+	srand(UINT_MAX);
+	c = rand();
+	zassert_equal(c, 1043980748, "srand with seed UINT_MAX failed (3rd)");
+}
+
 /**
  *
  * @brief test abort functions
@@ -966,6 +1072,9 @@ void test_main(void)
 			 ztest_unit_test(test_memcpy),
 			 ztest_unit_test(test_memmove),
 			 ztest_unit_test(test_time),
+			 ztest_unit_test(test_rand),
+			 ztest_unit_test(test_srand),
+			 ztest_unit_test(test_rand_reproducibility),
 			 ztest_unit_test(test_abort),
 			 ztest_unit_test(test_exit),
 			 ztest_unit_test(test_str_operate),