target/arm: Fix aa64 ldp register writeback

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>
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
Message-id: 20170825224833.4463-1-richard.henderson@linaro.org
Fixes: https://bugs.launchpad.net/qemu/+bug/1713066
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
[PMM: tweaked comment format]
Reviewed-by: Peter Maydell <peter.maydell@linaro.org>
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
(cherry picked from commit 3e4d91b94ce400326fae0850578d9e9f30a71adb)
Signed-off-by: Michael Roth <mdroth@linux.vnet.ibm.com>

diff --git a/target/arm/translate-a64.c b/target/arm/translate-a64.c
index 24de30d92cca7774230bb21ca493691d586c94d7..f793da58177482c95a0237acc682eb4ae5272ab9 100644 (file)
--- a/target/arm/translate-a64.c
+++ b/target/arm/translate-a64.c
@@ -2193,29 +2193,34 @@ 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);
         }