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>
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);