X-Git-Url: http://git.megacz.com/?a=blobdiff_plain;f=rts%2Fsm%2FBlockAlloc.c;h=ba9220ac42638e60ccf180ecdb0e5565ef0cb7c9;hb=cc94b30f3d854ed97ac6a7a54fa12247295219d4;hp=9d92c6bee109e1098d73283beb80373bf46b21f9;hpb=bdbb7f57adf98d4826e0c97b5eff9c45ceb3dbf2;p=ghc-hetmet.git

diff --git a/rts/sm/BlockAlloc.c b/rts/sm/BlockAlloc.c
index 9d92c6b..ba9220a 100644
--- a/rts/sm/BlockAlloc.c
+++ b/rts/sm/BlockAlloc.c
@@ -26,9 +26,6 @@
 
 static void  initMBlock(void *mblock);
 
-// The free_list is kept sorted by size, smallest first.
-// In THREADED_RTS mode, the free list is protected by sm_mutex.
-
 /* -----------------------------------------------------------------------------
 
   Implementation notes
@@ -121,8 +118,20 @@ static void  initMBlock(void *mblock);
 
   --------------------------------------------------------------------------- */
 
+/* ---------------------------------------------------------------------------
+   WATCH OUT FOR OVERFLOW
+
+   Be very careful with integer overflow here.  If you have an
+   expression like (n_blocks * BLOCK_SIZE), and n_blocks is an int or
+   a nat, then it will very likely overflow on a 64-bit platform.
+   Always cast to StgWord (or W_ for short) first: ((W_)n_blocks * BLOCK_SIZE).
+
+  --------------------------------------------------------------------------- */
+
 #define MAX_FREE_LIST 9
 
+// In THREADED_RTS mode, the free list is protected by sm_mutex.
+
 static bdescr *free_list[MAX_FREE_LIST];
 static bdescr *free_mblock_list;
 
@@ -338,7 +347,7 @@ allocGroup (nat n)
 
     if (ln == MAX_FREE_LIST) {
 #if 0
-        if ((mblocks_allocated * MBLOCK_SIZE_W - n_alloc_blocks * BLOCK_SIZE_W) > (1024*1024)/sizeof(W_)) {
+        if (((W_)mblocks_allocated * MBLOCK_SIZE_W - (W_)n_alloc_blocks * BLOCK_SIZE_W) > (1024*1024)/sizeof(W_)) {
             debugBelch("Fragmentation, wanted %d blocks:", n);
             RtsFlags.DebugFlags.block_alloc = 1;
             checkFreeListSanity();
@@ -473,7 +482,7 @@ freeGroup(bdescr *p)
   p->gen = NULL;
   p->gen_no = 0;
   /* fill the block group with garbage if sanity checking is on */
-  IF_DEBUG(sanity,memset(p->start, 0xaa, p->blocks * BLOCK_SIZE));
+  IF_DEBUG(sanity,memset(p->start, 0xaa, (W_)p->blocks * BLOCK_SIZE));
 
   if (p->blocks == 0) barf("freeGroup: block size is zero");
 
@@ -587,7 +596,7 @@ splitBlockGroup (bdescr *bd, nat blocks)
         low_mblocks = 1 + (blocks - BLOCKS_PER_MBLOCK) / (MBLOCK_SIZE / BLOCK_SIZE);
         high_mblocks = (bd->blocks - blocks) / (MBLOCK_SIZE / BLOCK_SIZE);
 
-        new_mblock = (void *) ((P_)MBLOCK_ROUND_DOWN(bd) + low_mblocks * MBLOCK_SIZE_W);
+        new_mblock = (void *) ((P_)MBLOCK_ROUND_DOWN(bd) + (W_)low_mblocks * MBLOCK_SIZE_W);
         initMBlock(new_mblock);
         new_bd = FIRST_BDESCR(new_mblock);
         new_bd->blocks = MBLOCK_GROUP_BLOCKS(high_mblocks);