[Qemu-devel] [PATCH v2 21/26] armv7m: CONTROL<1> handling

[Michael Davidsaver]

The ARM states that this bit indicates the stack
being used, which in handler mode is always MSP.
Further CONTROL<1>==1 in handler mode is reserved.

With the TM4C always CONTROL<1>==0 in handler mode
which inconveniently prevents the handler from
knowing which stack thread mode was using...

This bit is a direct indication of which stack pointer
register is "aliased" to r13, so easiest to eliminate
the now redundant current_sp field.
---
 target-arm/cpu.h     |  1 -
 target-arm/helper.c  | 20 ++++++++++----------
 target-arm/machine.c |  1 -
 3 files changed, 10 insertions(+), 12 deletions(-)

diff --git a/target-arm/cpu.h b/target-arm/cpu.h
index b93f8ae..01c9cdb 100644
--- a/target-arm/cpu.h
+++ b/target-arm/cpu.h
@@ -402,7 +402,6 @@ typedef struct CPUARMState {
         uint32_t mmfar; /* MemManage Fault Address */
         uint32_t bfar; /* BusFault Address */
         unsigned mpu_hfnmiena; /* MPU_CTRL not mappable into SCTLR */
-        int current_sp;
         int exception;
         int exception_prio;
         unsigned pending;
diff --git a/target-arm/helper.c b/target-arm/helper.c
index a5adf2d..2661da4 100644
--- a/target-arm/helper.c
+++ b/target-arm/helper.c
@@ -5362,14 +5362,14 @@ static uint32_t v7m_pop(CPUARMState *env)
 }
 
 /* Switch to V7M main or process stack pointer.  */
-static void switch_v7m_sp(CPUARMState *env, int process)
+static void switch_v7m_sp(CPUARMState *env, bool process)
 {
     uint32_t tmp;
-    if (env->v7m.current_sp != process) {
+    if (!!(env->v7m.control & 2) != process) {
         tmp = env->v7m.other_sp;
         env->v7m.other_sp = env->regs[13];
         env->regs[13] = tmp;
-        env->v7m.current_sp = process;
+        env->v7m.control = (env->v7m.control & ~2) | (process ? 2 : 0);
     }
 }
 
@@ -5457,7 +5457,7 @@ static void do_v7m_exception_exit(CPUARMState *env)
     xpsr = v7m_pop(env);
     xpsr_write(env, xpsr, 0xfffffdff);
 
-    assert(env->v7m.exception!=-42);
+    assert(env->v7m.exception != -42);
 
     /* Undo stack alignment.  */
     if (xpsr & 0x200)
@@ -5528,7 +5528,7 @@ void arm_v7m_cpu_do_interrupt(CPUState *cs)
     arm_log_exception(cs->exception_index);
 
     lr = 0xfffffff1;
-    if (env->v7m.current_sp)
+    if (env->v7m.control & 2)
         lr |= 4;
     if (env->v7m.exception == 0)
         lr |= 8;
@@ -7550,9 +7550,9 @@ uint32_t HELPER(v7m_mrs)(CPUARMState *env, uint32_t reg)
 
     switch (reg) {
     case 8: /* MSP */
-        return env->v7m.current_sp ? env->v7m.other_sp : env->regs[13];
+        return env->v7m.control & 2 ? env->v7m.other_sp : env->regs[13];
     case 9: /* PSP */
-        return env->v7m.current_sp ? env->regs[13] : env->v7m.other_sp;
+        return env->v7m.control & 2 ? env->regs[13] : env->v7m.other_sp;
     case 16: /* PRIMASK */
         return (env->daif & PSTATE_I) != 0;
     case 17: /* BASEPRI */
@@ -7582,13 +7582,13 @@ void HELPER(v7m_msr)(CPUARMState *env, uint32_t reg, 
uint32_t val)
         }
         break;
     case 8: /* MSP */
-        if (env->v7m.current_sp)
+        if (env->v7m.control & 2)
             env->v7m.other_sp = val;
         else
             env->regs[13] = val;
         break;
     case 9: /* PSP */
-        if (env->v7m.current_sp)
+        if (env->v7m.control & 2)
             env->regs[13] = val;
         else
             env->v7m.other_sp = val;
@@ -7616,8 +7616,8 @@ void HELPER(v7m_msr)(CPUARMState *env, uint32_t reg, 
uint32_t val)
         }
         break;
     case 20: /* CONTROL */
-        env->v7m.control = val & 3;
         switch_v7m_sp(env, (val & 2) != 0);
+        env->v7m.control = (env->v7m.control & ~1) | (val & 1);
         break;
     default:
         qemu_log_mask(LOG_GUEST_ERROR, "Attempt to write unknown special"
diff --git a/target-arm/machine.c b/target-arm/machine.c
index 8852410..dab1626 100644
--- a/target-arm/machine.c
+++ b/target-arm/machine.c
@@ -105,7 +105,6 @@ static const VMStateDescription vmstate_m = {
         VMSTATE_UINT32(env.v7m.hfsr, ARMCPU),
         VMSTATE_UINT32(env.v7m.mmfar, ARMCPU),
         VMSTATE_UINT32(env.v7m.bfar, ARMCPU),
-        VMSTATE_INT32(env.v7m.current_sp, ARMCPU),
         VMSTATE_UINT32(env.v7m.mpu_hfnmiena, ARMCPU),
         VMSTATE_INT32(env.v7m.exception, ARMCPU),
         VMSTATE_END_OF_LIST()
-- 
2.1.4