rts/m32: Fix bounds checkwip/fix-m32

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.

1 files changed, 3 insertions, 2 deletions

diff --git a/rts/linker/M32Alloc.c b/rts/linker/M32Alloc.c
index e7c697bf60..cd8751b3b0 100644
--- a/rts/linker/M32Alloc.c
+++ b/rts/linker/M32Alloc.c
@@ -244,8 +244,9 @@ m32_alloc_page(void)
      * pages.
      */
     const size_t pgsz = getPageSize();
-    uint8_t *chunk = mmapAnonForLinker(pgsz * M32_MAP_PAGES);
-    if (chunk > (uint8_t *) 0xffffffff) {
+    const size_t map_sz = pgsz * M32_MAP_PAGES;
+    uint8_t *chunk = mmapAnonForLinker(map_sz);
+    if (chunk + map_sz > (uint8_t *) 0xffffffff) {
       barf("m32_alloc_page: failed to get allocation in lower 32-bits");
     }