diff options
Diffstat (limited to 'rts/StablePtr.c')
| -rw-r--r-- | rts/StablePtr.c | 21 |
1 files changed, 19 insertions, 2 deletions
diff --git a/rts/StablePtr.c b/rts/StablePtr.c index ffd1d0775a..c2e7cda2c3 100644 --- a/rts/StablePtr.c +++ b/rts/StablePtr.c @@ -88,6 +88,16 @@ https://gitlab.haskell.org/ghc/ghc/issues/7670 for details. */ +/* + * Note [NULL StgStablePtr] + * ~~~~~~~~~~~~~~~~~~~~~~~~ + * + * StablePtr index 0 is reserved to represent NULL. Consequently, we must + * subtract 1 to get the index into the array and add 1 to the index to get the + * StablePtr. + */ + + spEntry *stable_ptr_table = NULL; static spEntry *stable_ptr_free = NULL; static unsigned int SPT_size = 0; @@ -255,8 +265,13 @@ freeSpEntry(spEntry *sp) void freeStablePtrUnsafe(StgStablePtr sp) { - ASSERT((StgWord)sp < SPT_size); - freeSpEntry(&stable_ptr_table[(StgWord)sp]); + // see Note [NULL StgStablePtr] + if (sp == NULL) { + return; + } + StgWord spw = (StgWord)sp - 1; + ASSERT(spw < SPT_size); + freeSpEntry(&stable_ptr_table[spw]); } void @@ -282,6 +297,8 @@ getStablePtr(StgPtr p) stable_ptr_free = (spEntry*)(stable_ptr_free->addr); RELAXED_STORE(&stable_ptr_table[sp].addr, p); stablePtrUnlock(); + // see Note [NULL StgStablePtr] + sp = sp + 1; return (StgStablePtr)(sp); } |