target-arm: Set PSTATE.SS correctly on exception return from AArch64

Set the PSTATE.SS bit correctly on exception returns from AArch64,
as required by the debug single-step functionality.

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Edgar E. Iglesias <edgar.iglesias@xilinx.com>

1 files changed, 20 insertions, 0 deletions

diff --git a/target-arm/op_helper.c b/target-arm/op_helper.c
index 180a4a096b..62cc07d448 100644
--- a/target-arm/op_helper.c
+++ b/target-arm/op_helper.c
@@ -380,12 +380,26 @@ void HELPER(exception_return)(CPUARMState *env)
 
     env->exclusive_addr = -1;
 
+    /* We must squash the PSTATE.SS bit to zero unless both of the
+     * following hold:
+     *  1. debug exceptions are currently disabled
+     *  2. singlestep will be active in the EL we return to
+     * We check 1 here and 2 after we've done the pstate/cpsr write() to
+     * transition to the EL we're going to.
+     */
+    if (arm_generate_debug_exceptions(env)) {
+        spsr &= ~PSTATE_SS;
+    }
+
     if (spsr & PSTATE_nRW) {
         /* TODO: We currently assume EL1/2/3 are running in AArch64.  */
         env->aarch64 = 0;
         new_el = 0;
         env->uncached_cpsr = 0x10;
         cpsr_write(env, spsr, ~0);
+        if (!arm_singlestep_active(env)) {
+            env->uncached_cpsr &= ~PSTATE_SS;
+        }
         for (i = 0; i < 15; i++) {
             env->regs[i] = env->xregs[i];
         }
@@ -410,6 +424,9 @@ void HELPER(exception_return)(CPUARMState *env)
         }
         env->aarch64 = 1;
         pstate_write(env, spsr);
+        if (!arm_singlestep_active(env)) {
+            env->pstate &= ~PSTATE_SS;
+        }
         aarch64_restore_sp(env, new_el);
         env->pc = env->elr_el[cur_el];
     }
@@ -429,6 +446,9 @@ illegal_return:
     spsr &= PSTATE_NZCV | PSTATE_DAIF;
     spsr |= pstate_read(env) & ~(PSTATE_NZCV | PSTATE_DAIF);
     pstate_write(env, spsr);
+    if (!arm_singlestep_active(env)) {
+        env->pstate &= ~PSTATE_SS;
+    }
 }
 
 /* ??? Flag setting arithmetic is awkward because we need to do comparisons.