From 5801fcb2b36e04c433dcf0b90a8c47b86e34fc07 Mon Sep 17 00:00:00 2001 From: =?UTF-8?q?Bj=C3=B6rn=20Gustavsson?= Date: Sun, 2 Sep 2018 08:42:51 +0200 Subject: ops.tab: Fix potentially unsafe optimization of raise/2 The operands for the raise/2 instruction are almost always in x(2) and x(1). Therefore the loader translates the raise/2 instruction to an i_raise/0 instruction which uses the values in x(2) and x(1). If the operands happens to be in other registers, the loader inserts move/2 instruction to move them to x(2) and x(1). The problem is that x(3) is used as a temporary register when generating the move/2 instructions. That is unsafe if the Value operand for raise/2 is x(3). Thus: raise x(0) x(3) will be translated to: move x(0) x(3) move x(3) x(1) move x(3) x(2) i_raise The Trace will be written to both x(2) and x(1). The current compiler will never use x(3) for the Value operand, so there is no need to patch previous releases. But a future compiler version might allocate registers differently. --- erts/emulator/beam/ops.tab | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/erts/emulator/beam/ops.tab b/erts/emulator/beam/ops.tab index c51e4ef784..e76d896ffc 100644 --- a/erts/emulator/beam/ops.tab +++ b/erts/emulator/beam/ops.tab @@ -244,7 +244,7 @@ if_end # Optimize for that case. raise x==2 x==1 => i_raise raise Trace=y Value=y => move Trace x=2 | move Value x=1 | i_raise -raise Trace Value => move Trace x=3 | move Value x=1 | move x=3 x=2 | i_raise +raise Trace Value => move Trace x | move Value x=1 | move x x=2 | i_raise i_raise -- cgit v1.2.3