1 files changed, 79 insertions, 0 deletions

diff --git a/target/arm/helper.c b/target/arm/helper.c
index 00807b4053..329e5178d8 100644
--- a/target/arm/helper.c
+++ b/target/arm/helper.c
@@ -5870,6 +5870,12 @@ uint32_t HELPER(v7m_mrs)(CPUARMState *env, uint32_t reg)
     return 0;
 }
 
+void HELPER(v7m_bxns)(CPUARMState *env, uint32_t dest)
+{
+    /* translate.c should never generate calls here in user-only mode */
+    g_assert_not_reached();
+}
+
 void switch_mode(CPUARMState *env, int mode)
 {
     ARMCPU *cpu = arm_env_get_cpu(env);
@@ -6044,6 +6050,18 @@ static uint32_t v7m_pop(CPUARMState *env)
     return val;
 }
 
+/* Return true if we're using the process stack pointer (not the MSP) */
+static bool v7m_using_psp(CPUARMState *env)
+{
+    /* Handler mode always uses the main stack; for thread mode
+     * the CONTROL.SPSEL bit determines the answer.
+     * Note that in v7M it is not possible to be in Handler mode with
+     * CONTROL.SPSEL non-zero, but in v8M it is, so we must check both.
+     */
+    return !arm_v7m_is_handler_mode(env) &&
+        env->v7m.control[env->v7m.secure] & R_V7M_CONTROL_SPSEL_MASK;
+}
+
 /* Switch to V7M main or process stack pointer.  */
 static void switch_v7m_sp(CPUARMState *env, bool new_spsel)
 {
@@ -6062,6 +6080,67 @@ static void switch_v7m_sp(CPUARMState *env, bool new_spsel)
     }
 }
 
+/* Switch M profile security state between NS and S */
+static void switch_v7m_security_state(CPUARMState *env, bool new_secstate)
+{
+    uint32_t new_ss_msp, new_ss_psp;
+
+    if (env->v7m.secure == new_secstate) {
+        return;
+    }
+
+    /* All the banked state is accessed by looking at env->v7m.secure
+     * except for the stack pointer; rearrange the SP appropriately.
+     */
+    new_ss_msp = env->v7m.other_ss_msp;
+    new_ss_psp = env->v7m.other_ss_psp;
+
+    if (v7m_using_psp(env)) {
+        env->v7m.other_ss_psp = env->regs[13];
+        env->v7m.other_ss_msp = env->v7m.other_sp;
+    } else {
+        env->v7m.other_ss_msp = env->regs[13];
+        env->v7m.other_ss_psp = env->v7m.other_sp;
+    }
+
+    env->v7m.secure = new_secstate;
+
+    if (v7m_using_psp(env)) {
+        env->regs[13] = new_ss_psp;
+        env->v7m.other_sp = new_ss_msp;
+    } else {
+        env->regs[13] = new_ss_msp;
+        env->v7m.other_sp = new_ss_psp;
+    }
+}
+
+void HELPER(v7m_bxns)(CPUARMState *env, uint32_t dest)
+{
+    /* Handle v7M BXNS:
+     *  - if the return value is a magic value, do exception return (like BX)
+     *  - otherwise bit 0 of the return value is the target security state
+     */
+    if (dest >= 0xff000000) {
+        /* This is an exception return magic value; put it where
+         * do_v7m_exception_exit() expects and raise EXCEPTION_EXIT.
+         * Note that if we ever add gen_ss_advance() singlestep support to
+         * M profile this should count as an "instruction execution complete"
+         * event (compare gen_bx_excret_final_code()).
+         */
+        env->regs[15] = dest & ~1;
+        env->thumb = dest & 1;
+        HELPER(exception_internal)(env, EXCP_EXCEPTION_EXIT);
+        /* notreached */
+    }
+
+    /* translate.c should have made BXNS UNDEF unless we're secure */
+    assert(env->v7m.secure);
+
+    switch_v7m_security_state(env, dest & 1);
+    env->thumb = 1;
+    env->regs[15] = dest & ~1;
+}
+
 static uint32_t arm_v7m_load_vector(ARMCPU *cpu)
 {
     CPUState *cs = CPU(cpu);