From: Laurent Vivier <laurent@vivier.eu>
Date: Wed, 14 Jun 2017 20:39:05 +0000 (+0200)
Subject: target/m68k: fix V flag for CC_OP_SUBx
X-Git-Tag: v2.11.1~471^2~3
X-Git-Url: https://git.proxmox.com/?a=commitdiff_plain;h=043b936ef6fe53396b3c6b8f5562ea3e238a071d;p=mirror_qemu.git

target/m68k: fix V flag for CC_OP_SUBx

V flag for subtraction is:

   v = (res ^ src1) & (src1 ^ src2)

(see COMPUTE_CCR() in target/m68k/helper.c)

But gen_flush_flags() uses:

   v = (res ^ src2) & (src1 ^ src2)

The problem has been found with the following program:

        .global _start
_start:
        move.l  #-2147483648,%d0
        subq.l  #1,%d0
        jvc     1f
        move.l #1,%d1
        move.l #1,%d0
        trap #0
1:
        move.l #0,%d1
        move.l #1,%d0
        trap #0

It works fine (exit(1)) on real hardware, and with "-singlestep".

"-singlestep" uses gen_helper_flush_flags(), whereas
without "-singlestep", V flag is computed directly in
gen_flush_flags().

This patch updates gen_flush_flags() to have the same result
as with gen_helper_flush_flags().

Signed-off-by: Laurent Vivier <laurent@vivier.eu>
Reviewed-by: Richard Henderson <rth@twiddle.net>
Message-Id: <20170614203905.19657-1-laurent@vivier.eu>
---

diff --git a/target/m68k/translate.c b/target/m68k/translate.c
index ad4d4efb8d..52653f67e5 100644
--- a/target/m68k/translate.c
+++ b/target/m68k/translate.c
@@ -565,7 +565,7 @@ static void gen_flush_flags(DisasContext *s)
         t1 = tcg_temp_new();
         tcg_gen_add_i32(t0, QREG_CC_N, QREG_CC_V);
         gen_ext(t0, t0, s->cc_op - CC_OP_SUBB, 1);
-        tcg_gen_xor_i32(t1, QREG_CC_N, QREG_CC_V);
+        tcg_gen_xor_i32(t1, QREG_CC_N, t0);
         tcg_gen_xor_i32(QREG_CC_V, QREG_CC_V, t0);
         tcg_temp_free(t0);
         tcg_gen_and_i32(QREG_CC_V, QREG_CC_V, t1);