rts/m32: Fix bounds check

Previously we would check only that the *start* of the mapping was in
the bottom 32-bits of address space. However, we need the *entire*
mapping to be in low memory. Fix this.

Noticed by @Phyx.

(cherry picked from commit 72c1812feecd2aff2a96b629063ba90a2f4cdb7b)

1 files changed, 4 insertions, 3 deletions

diff --git a/rts/linker/M32Alloc.c b/rts/linker/M32Alloc.c
index 1a19df8471..ae4d1ae891 100644
--- a/rts/linker/M32Alloc.c
+++ b/rts/linker/M32Alloc.c
@@ -256,11 +256,12 @@ m32_alloc_page(void)
     m32_free_page_pool_size --;
     return page;
   } else {
-    struct m32_page_t *page = mmapForLinker(getPageSize(),MAP_ANONYMOUS,-1,0);
-    if (page > (struct m32_page_t *) 0xffffffff) {
+    const size_t map_sz = getPageSize();
+    uint8_t *page = mmapForLinker(map_sz,MAP_ANONYMOUS,-1,0);
+    if (page + map_sz > (uint8_t *) 0xffffffff) {
       barf("m32_alloc_page: failed to get allocation in lower 32-bits");
     }
-    return page;
+    return (struct m32_page_t *) page;
   }
 }