syscalls.c: Allow environment to specify heap boundaries.

Rename HEAP_START/HEAP_END macros CONFIG_HEAP_START/CONFIG_HEAP_END,
to mark them as build-time configuration options.  Wrap their
definitions with #ifndefs appropriately.

1 files changed, 12 insertions, 6 deletions

diff --git a/libmaple/syscalls.c b/libmaple/syscalls.c
index a3f12f1..9193a17 100644
--- a/libmaple/syscalls.c
+++ b/libmaple/syscalls.c
@@ -29,12 +29,17 @@
 #include <sys/stat.h>
 #include <errno.h>
 
-/* Set by the linker */
+/* If CONFIG_HEAP_START (or CONFIG_HEAP_END) isn't defined, then
+ * assume _lm_heap_start (resp. _lm_heap_end) is appropriately set by
+ * the linker */
+#ifndef CONFIG_HEAP_START
 extern char _lm_heap_start;
+#define CONFIG_HEAP_START               ((caddr_t)&_lm_heap_start)
+#endif
+#ifndef CONFIG_HEAP_END
 extern char _lm_heap_end;
-
-#define HEAP_START           ((caddr_t)&_lm_heap_start)
-#define HEAP_END             ((caddr_t)&_lm_heap_end)
+#define CONFIG_HEAP_END                 ((caddr_t)&_lm_heap_end)
+#endif
 
 /*
  * _sbrk -- Increment the program break.
@@ -47,10 +52,11 @@ caddr_t _sbrk(int incr) {
     caddr_t ret;
 
     if (pbreak == NULL) {
-        pbreak = HEAP_START;
+        pbreak = CONFIG_HEAP_START;
     }
 
-    if ((HEAP_END - pbreak < incr) || (pbreak - HEAP_START < -incr)) {
+    if ((CONFIG_HEAP_END - pbreak < incr) ||
+        (pbreak - CONFIG_HEAP_START < -incr)) {
         errno = ENOMEM;
         return (caddr_t)-1;
     }