[PATCH v2 1/2] target/s390x/tcg: Set STCK/STCKF condition code after the store

[Ilya Leoshkevich <iii@linux.ibm.com>]

STORE CLOCK [FAST] to an inaccessible address aborts QEMU:

  $ qemu-s390x ./stckf
  ERROR:cc_helper.c:128:cc_calc_addu: assertion failed: (carry_out <= 1)

op_stck() sets the condition code with gen_op_movi_cc() before the
output operand store, which is deferred to wout_m1_64(). Assigning a
constant condition code discards the lazy CC values, so the optimizer
drops the writes that produced them. When the store then raises an
exception, the instruction is suppressed and
s390x_restore_state_to_opc() reinstates the cc_op recorded at the start
of STCK[F], but cc_src/cc_dst now hold stale values, so the next
condition code evaluation reads garbage.

Fix by performing the store manually. The alternative of not discarding
in gen_op_movi_cc() keeps the inputs live, but results in less optimal
code.

Reported-by: Ido Plat <Ido.Plat1@ibm.com>
Fixes: 434c91a5f4ed ("target-s390: Convert STCK")
Cc: qemu-stable@nongnu.org
Signed-off-by: Ilya Leoshkevich <iii@linux.ibm.com>
---
 target/s390x/tcg/insn-data.h.inc | 4 ++--
 target/s390x/tcg/translate.c     | 2 ++
 2 files changed, 4 insertions(+), 2 deletions(-)

diff --git a/target/s390x/tcg/insn-data.h.inc b/target/s390x/tcg/insn-data.h.inc
index 0d5392eac54..1ea72248a6a 100644
--- a/target/s390x/tcg/insn-data.h.inc
+++ b/target/s390x/tcg/insn-data.h.inc
@@ -887,8 +887,8 @@
     C(0xe32f, STRVG,   RXY_a, Z,   la2, r1_o, new, m1_64, rev64, 0)
 
 /* STORE CLOCK */
-    F(0xb205, STCK,    S,     Z,   la2, 0, new, m1_64, stck, 0, IF_IO)
-    F(0xb27c, STCKF,   S,     SCF, la2, 0, new, m1_64, stck, 0, IF_IO)
+    F(0xb205, STCK,    S,     Z,   la2, 0, new, 0, stck, 0, IF_IO)
+    F(0xb27c, STCKF,   S,     SCF, la2, 0, new, 0, stck, 0, IF_IO)
 /* STORE CLOCK EXTENDED */
     F(0xb278, STCKE,   S,     Z,   0, a2, 0, 0, stcke, 0, IF_IO)
 
diff --git a/target/s390x/tcg/translate.c b/target/s390x/tcg/translate.c
index 82165ac1ec0..1b6023168bb 100644
--- a/target/s390x/tcg/translate.c
+++ b/target/s390x/tcg/translate.c
@@ -4108,7 +4108,9 @@ static DisasJumpType op_stap(DisasContext *s, DisasOps *o)
 static DisasJumpType op_stck(DisasContext *s, DisasOps *o)
 {
     gen_helper_stck(o->out, tcg_env);
+    tcg_gen_qemu_st_i64(o->out, o->addr1, get_mem_index(s), MO_BEUQ);
     /* ??? We don't implement clock states.  */
+    /* Set the CC after the store; a suppressed store must preserve it. */
     gen_op_movi_cc(s, 0);
     return DISAS_NEXT;
 }
-- 
2.55.0