rts/M32Alloc: Don't attempt to unmap non-existent pageswip/fix-m32-unmap

The m32 allocator's `pages` list may contain NULLs in the case that the
page was flushed. Some `munmap` implementations (e.g. FreeBSD's) don't
like it if we pass them NULL. Don't do that.

1 files changed, 3 insertions, 1 deletions

diff --git a/rts/linker/M32Alloc.c b/rts/linker/M32Alloc.c
index 6f61a5c447..1a19df8471 100644
--- a/rts/linker/M32Alloc.c
+++ b/rts/linker/M32Alloc.c
@@ -317,7 +317,9 @@ void m32_allocator_free(m32_allocator *alloc)
   /* free partially-filled pages */
   const size_t pgsz = getPageSize();
   for (int i=0; i < M32_MAX_PAGES; i++) {
-    munmapForLinker(alloc->pages[i], pgsz);
+    if (alloc->pages[i]) {
+      munmapForLinker(alloc->pages[i], pgsz);
+    }
   }
 
   stgFree(alloc);