The new x86 decoder wants the gen_* functions to compute EFLAGS before
writeback, which can be an issue for instructions with a memory
destination such as ARPL or shifts.

Extract code to compute the EFLAGS without clobbering CC_SRC, in case
the memory write causes a fault.  The flags writeback mechanism will
take care of copying the result to CC_SRC.

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
---
 target/i386/tcg/translate.c | 28 +++++++++++++++++++---------
 1 file changed, 19 insertions(+), 9 deletions(-)

diff --git a/target/i386/tcg/translate.c b/target/i386/tcg/translate.c
index 00ed0cc9a31..b79c312465b 100644
--- a/target/i386/tcg/translate.c
+++ b/target/i386/tcg/translate.c
@@ -862,22 +862,22 @@ static void gen_op_update_neg_cc(DisasContext *s)
     tcg_gen_movi_tl(s->cc_srcT, 0);
 }
 
-/* compute all eflags to cc_src */
-static void gen_compute_eflags(DisasContext *s)
+/* compute all eflags to reg */
+static void gen_mov_eflags(DisasContext *s, TCGv reg)
 {
-    TCGv zero, dst, src1, src2;
+    TCGv dst, src1, src2;
+    TCGv_i32 cc_op;
     int live, dead;
 
     if (s->cc_op == CC_OP_EFLAGS) {
+        tcg_gen_mov_tl(reg, cpu_cc_src);
         return;
     }
     if (s->cc_op == CC_OP_CLR) {
-        tcg_gen_movi_tl(cpu_cc_src, CC_Z | CC_P);
-        set_cc_op(s, CC_OP_EFLAGS);
+        tcg_gen_movi_tl(reg, CC_Z | CC_P);
         return;
     }
 
-    zero = NULL;
     dst = cpu_cc_dst;
     src1 = cpu_cc_src;
     src2 = cpu_cc_src2;
@@ -886,7 +886,7 @@ static void gen_compute_eflags(DisasContext *s)
     live = cc_op_live[s->cc_op] & ~USES_CC_SRCT;
     dead = live ^ (USES_CC_DST | USES_CC_SRC | USES_CC_SRC2);
     if (dead) {
-        zero = tcg_constant_tl(0);
+        TCGv zero = tcg_constant_tl(0);
         if (dead & USES_CC_DST) {
             dst = zero;
         }
@@ -898,8 +898,18 @@ static void gen_compute_eflags(DisasContext *s)
         }
     }
 
-    gen_update_cc_op(s);
-    gen_helper_cc_compute_all(cpu_cc_src, dst, src1, src2, cpu_cc_op);
+    if (s->cc_op != CC_OP_DYNAMIC) {
+        cc_op = tcg_constant_i32(s->cc_op);
+    } else {
+        cc_op = cpu_cc_op;
+    }
+    gen_helper_cc_compute_all(reg, dst, src1, src2, cc_op);
+}
+
+/* compute all eflags to cc_src */
+static void gen_compute_eflags(DisasContext *s)
+{
+    gen_mov_eflags(s, cpu_cc_src);
     set_cc_op(s, CC_OP_EFLAGS);
 }
 
-- 
2.43.0

On 12/23/23 05:15, Paolo Bonzini wrote:
> The new x86 decoder wants the gen_* functions to compute EFLAGS before
> writeback, which can be an issue for instructions with a memory
> destination such as ARPL or shifts.
> 
> Extract code to compute the EFLAGS without clobbering CC_SRC, in case
> the memory write causes a fault.  The flags writeback mechanism will
> take care of copying the result to CC_SRC.
> 
> Signed-off-by: Paolo Bonzini<pbonzini@redhat.com>
> ---
>   target/i386/tcg/translate.c | 28 +++++++++++++++++++---------
>   1 file changed, 19 insertions(+), 9 deletions(-)

Reviewed-by: Richard Henderson <richard.henderson@linaro.org>

r~