[Qemu-devel] [PATCH] target/arm: Fix aa64 ldp register writeback

[Richard Henderson <richard.henderson@linaro.org>]

For "ldp x0, x1, [x0]", if the second load is on a second page and
the second page is unmapped, the exception would be raised with x0
already modified.  This means the instruction couldn't be restarted.

Cc: qemu-arm@nongnu.org
Cc: qemu-stable@nongnu.org
Reported-by: Andrew <andrew@fubar.geek.nz>
Fixes: https://bugs.launchpad.net/qemu/+bug/1713066
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
---
 target/arm/translate-a64.c | 28 ++++++++++++++++------------
 1 file changed, 16 insertions(+), 12 deletions(-)

diff --git a/target/arm/translate-a64.c b/target/arm/translate-a64.c
index c596025b04..bfba816a77 100644
--- a/target/arm/translate-a64.c
+++ b/target/arm/translate-a64.c
@@ -2217,29 +2217,33 @@ static void disas_ldst_pair(DisasContext *s, uint32_t insn)
         } else {
             do_fp_st(s, rt, tcg_addr, size);
         }
-    } else {
-        TCGv_i64 tcg_rt = cpu_reg(s, rt);
-        if (is_load) {
-            do_gpr_ld(s, tcg_rt, tcg_addr, size, is_signed, false,
-                      false, 0, false, false);
-        } else {
-            do_gpr_st(s, tcg_rt, tcg_addr, size,
-                      false, 0, false, false);
-        }
-    }
-    tcg_gen_addi_i64(tcg_addr, tcg_addr, 1 << size);
-    if (is_vector) {
+        tcg_gen_addi_i64(tcg_addr, tcg_addr, 1 << size);
         if (is_load) {
             do_fp_ld(s, rt2, tcg_addr, size);
         } else {
             do_fp_st(s, rt2, tcg_addr, size);
         }
     } else {
+        TCGv_i64 tcg_rt = cpu_reg(s, rt);
         TCGv_i64 tcg_rt2 = cpu_reg(s, rt2);
+
         if (is_load) {
+            TCGv_i64 tmp = tcg_temp_new_i64();
+
+            /* Do not modify tcg_rt before recognizing any exception
+               from the second load.  */
+            do_gpr_ld(s, tmp, tcg_addr, size, is_signed, false,
+                      false, 0, false, false);
+            tcg_gen_addi_i64(tcg_addr, tcg_addr, 1 << size);
             do_gpr_ld(s, tcg_rt2, tcg_addr, size, is_signed, false,
                       false, 0, false, false);
+
+            tcg_gen_mov_i64(tcg_rt, tmp);
+            tcg_temp_free_i64(tmp);
         } else {
+            do_gpr_st(s, tcg_rt, tcg_addr, size,
+                      false, 0, false, false);
+            tcg_gen_addi_i64(tcg_addr, tcg_addr, 1 << size);
             do_gpr_st(s, tcg_rt2, tcg_addr, size,
                       false, 0, false, false);
         }
-- 
2.13.5