add dummy_malloc functions

For some environments the dummy malloc functions offer a very small
alternative implementation. malloc will get its memory from sbrk()
and never frees memory again.
This of course is not suitable for interactive environments and thus
depends on CONFIG_SHELL_NONE

Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>

common/Kconfig

@@ -148,6 +148,22 @@ config EXPERIMENTAL
 	bool
 	prompt "Prompt for experimental code"
 
+choice
+	prompt "malloc implementation"
+
+config MALLOC_DLMALLOC
+	bool "dlmalloc"
+
+config MALLOC_DUMMY
+	bool "dummy malloc"
+	depends on SHELL_NONE
+	help
+	  select this option to use a dummy malloc implementation. With this
+	  memory is never freed. This is suitable for well tested noninteractive
+	  environments only.
+
+endchoice
+
 config MODULES
 	depends on HAS_MODULES
 	depends on EXPERIMENTAL

common/Makefile

@@ -9,7 +9,8 @@ obj-$(CONFIG_POLLER)		+= poller.o
 obj-$(CONFIG_BLOCK)		+= block.o
 
 obj-y += memory.o
-obj-y += dlmalloc.o
+obj-$(CONFIG_MALLOC_DLMALLOC) += dlmalloc.o
+obj-$(CONFIG_MALLOC_DUMMY) += dummy_malloc.o
 obj-y += clock.o
 obj-y += version.o
 obj-$(CONFIG_COMMAND_SUPPORT) += command.o

common/dummy_malloc.c

@@ -0,0 +1,26 @@
+#include <common.h>
+#include <malloc.h>
+
+void *memalign(size_t alignment, size_t bytes)
+{
+	unsigned long mem = (unsigned long)sbrk(bytes + alignment);
+
+	mem = (mem + alignment) & ~(alignment - 1);
+
+	return (void *)mem;
+}
+
+void *malloc(size_t size)
+{
+	return memalign(8, size);
+}
+
+void free(void *ptr)
+{
+}
+
+void *realloc(void *ptr, size_t size)
+{
+	BUG();
+}
+