|
 |
560544 |
commit 256cf43c5eadb28edb45436aca6fda8ee55eb10e
|
|
|
560544 |
Author: Mark Wielaard <mark@klomp.org>
|
|
|
560544 |
Date: Thu Feb 21 17:21:53 2019 +0100
|
|
|
560544 |
|
|
|
560544 |
memcheck powerpc subfe x, x, x initializes x to 0 or -1 based on CA
|
|
|
560544 |
|
|
|
560544 |
GCC might use subfe x, x, x to initialize x to 0 or -1, based on
|
|
|
560544 |
whether the carry flag is set. This happens in some cases when g++
|
|
|
560544 |
compiles resetting a unique_ptr. The "trick" used by the compiler is
|
|
|
560544 |
that it can AND a pointer with the register x (now 0x0 or 0xffffffff)
|
|
|
560544 |
to set something to NULL or to the given pointer.
|
|
|
560544 |
|
|
|
560544 |
subfe is implemented as rD = (log not)rA + rB + XER[CA]
|
|
|
560544 |
if we instead implement it as rD = rB - rA - (XER[CA] ^ 1)
|
|
|
560544 |
then memcheck can see that rB and Ra cancel each other out if they
|
|
|
560544 |
are the same.
|
|
|
560544 |
|
|
|
560544 |
https://bugs.kde.org/show_bug.cgi?id=404054
|
|
|
560544 |
|
|
|
560544 |
diff --git a/VEX/priv/guest_ppc_toIR.c b/VEX/priv/guest_ppc_toIR.c
|
|
|
560544 |
index e207642..00ae6df 100644
|
|
|
560544 |
--- a/VEX/priv/guest_ppc_toIR.c
|
|
|
560544 |
+++ b/VEX/priv/guest_ppc_toIR.c
|
|
|
560544 |
@@ -5361,11 +5361,15 @@ static Bool dis_int_arith ( UInt theInstr )
|
|
|
560544 |
flag_OE ? "o" : "", flag_rC ? ".":"",
|
|
|
560544 |
rD_addr, rA_addr, rB_addr);
|
|
|
560544 |
// rD = (log not)rA + rB + XER[CA]
|
|
|
560544 |
+ // ==>
|
|
|
560544 |
+ // rD = rB - rA - (XER[CA] ^ 1)
|
|
|
560544 |
assign( old_xer_ca, mkWidenFrom32(ty, getXER_CA_32(), False) );
|
|
|
560544 |
- assign( rD, binop( mkSzOp(ty, Iop_Add8),
|
|
|
560544 |
- unop( mkSzOp(ty, Iop_Not8), mkexpr(rA)),
|
|
|
560544 |
- binop( mkSzOp(ty, Iop_Add8),
|
|
|
560544 |
- mkexpr(rB), mkexpr(old_xer_ca))) );
|
|
|
560544 |
+ assign( rD, binop( mkSzOp(ty, Iop_Sub8),
|
|
|
560544 |
+ binop( mkSzOp(ty, Iop_Sub8),
|
|
|
560544 |
+ mkexpr(rB), mkexpr(rA)),
|
|
|
560544 |
+ binop(mkSzOp(ty, Iop_Xor8),
|
|
|
560544 |
+ mkexpr(old_xer_ca),
|
|
|
560544 |
+ mkSzImm(ty, 1))) );
|
|
|
560544 |
set_XER_CA_CA32( ty, PPCG_FLAG_OP_SUBFE,
|
|
|
560544 |
mkexpr(rD), mkexpr(rA), mkexpr(rB),
|
|
|
560544 |
mkexpr(old_xer_ca) );
|