libc/common: Add memalign

lib/libc/common/source/stdlib/malloc.c

@@ -153,6 +153,27 @@ void *aligned_alloc(size_t alignment, size_t size)
 	return ret;
 }
 
+#ifdef CONFIG_GLIBCXX_LIBCPP
+
+/*
+ * GCC's libstdc++ may use this function instead of aligned_alloc due to a
+ * bug in the configuration for "newlib" environments (which includes picolibc).
+ * When toolchains including that bug fix can become a dependency for Zephyr,
+ * this work-around can be removed.
+ *
+ * Note that aligned_alloc isn't defined to work as a replacement for
+ * memalign as it requires that the size be a multiple of the alignment,
+ * while memalign does not. However, the aligned_alloc implementation here
+ * is just a wrapper around sys_heap_aligned_alloc which doesn't have that
+ * requirement and so can be used by memalign.
+ */
+
+void *memalign(size_t alignment, size_t size)
+{
+	return aligned_alloc(alignment, size);
+}
+#endif
+
 static int malloc_prepare(void)
 {
 	void *heap_base = NULL;

tests/lib/cpp/libcxx/prj.conf

@@ -2,4 +2,5 @@ CONFIG_CPP=y
 CONFIG_STD_CPP17=y
 CONFIG_ZTEST=y
 CONFIG_ZTEST_STACK_SIZE=5120
+CONFIG_COMMON_LIBC_MALLOC_ARENA_SIZE=32768
 CONFIG_ZTEST_NEW_API=y

tests/lib/cpp/libcxx/src/main.cpp

@@ -9,6 +9,7 @@
 #include <memory>
 #include <vector>
 #include <zephyr/ztest.h>
+#include <zephyr/kernel.h>
 
 BUILD_ASSERT(__cplusplus == 201703);
 
@@ -95,6 +96,17 @@ ZTEST(libcxx_tests, test_exception)
 }
 #endif
 
+struct ThreadStack
+{
+	K_KERNEL_STACK_MEMBER(threadStack, 1024) {};
+};
+
+ZTEST(libcxx_tests, test_new_aligned)
+{
+	auto test_aligned = std::make_unique<ThreadStack>();
+	zassert_not_null(test_aligned, "aligned allocation failed");
+}
+
 static void *libcxx_tests_setup(void)
 {
 	TC_PRINT("version %u\n", (uint32_t)__cplusplus);