From 19972f42719c6e9357e33e123d00b681213022dc Mon Sep 17 00:00:00 2001 From: =?UTF-8?q?John=20H=C3=B6gberg?= Date: Tue, 23 Oct 2018 09:37:16 +0200 Subject: Fix trapping in lists:reverse/2 The first stage wasn't bounded by reductions, and it bumped far more reductions than it should have due to a logic bug. --- erts/emulator/beam/erl_bif_lists.c | 34 ++++++++++++++++++++-------------- 1 file changed, 20 insertions(+), 14 deletions(-) diff --git a/erts/emulator/beam/erl_bif_lists.c b/erts/emulator/beam/erl_bif_lists.c index 395be67a90..9b2b8aaab6 100644 --- a/erts/emulator/beam/erl_bif_lists.c +++ b/erts/emulator/beam/erl_bif_lists.c @@ -283,7 +283,7 @@ static BIF_RETTYPE lists_reverse_alloc(Process *c_p, { static const Uint CELLS_PER_RED = 40; - Eterm *heap_top, *heap_end; + Eterm *alloc_top, *alloc_end; Uint cells_left, max_cells; Eterm list, tail; Eterm lookahead; @@ -305,18 +305,18 @@ static BIF_RETTYPE lists_reverse_alloc(Process *c_p, BIF_ERROR(c_p, BADARG); } - heap_top = HAlloc(c_p, 2 * (max_cells - cells_left)); - heap_end = heap_top + 2 * (max_cells - cells_left); + alloc_top = HAlloc(c_p, 2 * (max_cells - cells_left)); + alloc_end = alloc_top + 2 * (max_cells - cells_left); - while (heap_top < heap_end) { + while (alloc_top < alloc_end) { Eterm *pair = list_val(list); - tail = CONS(heap_top, CAR(pair), tail); + tail = CONS(alloc_top, CAR(pair), tail); list = CDR(pair); ASSERT(is_list(list) || is_nil(list)); - heap_top += 2; + alloc_top += 2; } if (is_nil(list)) { @@ -333,7 +333,7 @@ static BIF_RETTYPE lists_reverse_onheap(Process *c_p, { static const Uint CELLS_PER_RED = 60; - Eterm *heap_top, *heap_end; + Eterm *alloc_start, *alloc_top, *alloc_end; Uint cells_left, max_cells; Eterm list, tail; @@ -343,21 +343,27 @@ static BIF_RETTYPE lists_reverse_onheap(Process *c_p, cells_left = max_cells = CELLS_PER_RED * (1 + ERTS_BIF_REDS_LEFT(c_p)); ASSERT(HEAP_LIMIT(c_p) >= HEAP_TOP(c_p) + 2); - heap_end = HEAP_LIMIT(c_p) - 2; - heap_top = HEAP_TOP(c_p); + alloc_start = HEAP_TOP(c_p); + alloc_end = HEAP_LIMIT(c_p) - 2; + alloc_top = alloc_start; - while (heap_top < heap_end && is_list(list)) { + /* Don't process more cells than we have reductions for. */ + alloc_end = MIN(alloc_top + (cells_left * 2), alloc_end); + + while (alloc_top < alloc_end && is_list(list)) { Eterm *pair = list_val(list); - tail = CONS(heap_top, CAR(pair), tail); + tail = CONS(alloc_top, CAR(pair), tail); list = CDR(pair); - heap_top += 2; + alloc_top += 2; } - cells_left -= (heap_top - heap_end) / 2; + cells_left -= (alloc_top - alloc_start) / 2; + HEAP_TOP(c_p) = alloc_top; + + ASSERT(cells_left >= 0 && cells_left <= max_cells); BUMP_REDS(c_p, (max_cells - cells_left) / CELLS_PER_RED); - HEAP_TOP(c_p) = heap_top; if (is_nil(list)) { BIF_RET(tail); -- cgit v1.2.1