diff options
Diffstat (limited to 'rts/Threads.c')
| -rw-r--r-- | rts/Threads.c | 13 |
1 files changed, 12 insertions, 1 deletions
diff --git a/rts/Threads.c b/rts/Threads.c index e1a401c9b3..fc9a895ed8 100644 --- a/rts/Threads.c +++ b/rts/Threads.c @@ -407,7 +407,18 @@ checkBlockingQueues (Capability *cap, StgTSO *tso) continue; } - p = bq->bh; + // We need to always ensure we untag bh. While it might seem a + // sensible assumption that bh will never be tagged, the GC could + // shortcut the indirection and put a tagged pointer into the + // indirection. + // + // This blew up on aarch64-darwin with misaligned access. bh pointing + // to an address that always ended in 0xa. Thus on architectures that + // are a little less strict about alignment, this would have read a + // garbage pinfo, which very, very unlikely would have been equal to + // stg_BLACKHOLE_info. Thus while the code would have done the wrong + // thing the result would be the same in almost all cases. See #20093. + p = UNTAG_CLOSURE(bq->bh); const StgInfoTable *pinfo = ACQUIRE_LOAD(&p->header.info); if (pinfo != &stg_BLACKHOLE_info || ((StgInd *)p)->indirectee != (StgClosure*)bq) |