[uheap] Add a generic external heap based on the system memory map

Add an implementation of umalloc() using the generalised model of a
heap, placing the external heap in the largest usable region obtained
from the system memory map.

Signed-off-by: Michael Brown <mcb30@ipxe.org>

src/include/ipxe/memmap.h

@@ -234,5 +234,6 @@ extern void memmap_update ( struct memmap_region *region, uint64_t start,
 			    uint64_t size, unsigned int flags,
 			    const char *name );
 extern void memmap_update_used ( struct memmap_region *region );
+extern size_t memmap_largest ( physaddr_t *start );
 
 #endif /* _IPXE_MEMMAP_H */

src/include/ipxe/uheap.h

@@ -0,0 +1,18 @@
+#ifndef _IPXE_UHEAP_H
+#define _IPXE_UHEAP_H
+
+/** @file
+ *
+ * External ("user") heap
+ *
+ */
+
+FILE_LICENCE ( GPL2_OR_LATER_OR_UBDL );
+
+#ifdef UMALLOC_UHEAP
+#define UMALLOC_PREFIX_uheap
+#else
+#define UMALLOC_PREFIX_uheap __uheap_
+#endif
+
+#endif /* _IPXE_UHEAP_H */

src/include/ipxe/umalloc.h

@@ -26,6 +26,7 @@ FILE_LICENCE ( GPL2_OR_LATER_OR_UBDL );
 	PROVIDE_SINGLE_API ( UMALLOC_PREFIX_ ## _subsys, _api_func, _func )
 
 /* Include all architecture-independent I/O API headers */
+#include <ipxe/uheap.h>
 #include <ipxe/efi/efi_umalloc.h>
 #include <ipxe/linux/linux_umalloc.h>