From 4a05e6139d756c0473df7a6dcb257074201f843d Mon Sep 17 00:00:00 2001 From: Simon Marlow Date: Tue, 5 Oct 2010 14:47:35 +0000 Subject: [PATCH] Fix a very rare crash in GHCi When a BCO with a zero-length bitmap was right at the edge of allocated memory, we were reading a word of non-existent memory. This showed up as a segfault in T789(ghci) for me, but the crash was extremely sensitive and went away with most changes. Also, optimised scavenge_large_bitmap a bit while I was in there. --- rts/sm/Scav.c | 24 +++++++++++------------- 1 file changed, 11 insertions(+), 13 deletions(-) diff --git a/rts/sm/Scav.c b/rts/sm/Scav.c index e59fc75..d01442b 100644 --- a/rts/sm/Scav.c +++ b/rts/sm/Scav.c @@ -1534,23 +1534,21 @@ scavenge_static(void) static void scavenge_large_bitmap( StgPtr p, StgLargeBitmap *large_bitmap, nat size ) { - nat i, b; + nat i, j, b; StgWord bitmap; b = 0; - bitmap = large_bitmap->bitmap[b]; - for (i = 0; i < size; ) { - if ((bitmap & 1) == 0) { - evacuate((StgClosure **)p); - } - i++; - p++; - if (i % BITS_IN(W_) == 0) { - b++; - bitmap = large_bitmap->bitmap[b]; - } else { + + for (i = 0; i < size; b++) { + bitmap = large_bitmap->bitmap[b]; + j = stg_min(size-i, BITS_IN(W_)); + i += j; + for (; j > 0; j--, p++) { + if ((bitmap & 1) == 0) { + evacuate((StgClosure **)p); + } bitmap = bitmap >> 1; - } + } } } -- 1.7.10.4