[PATCH 3/4] target/arm: Recalculate hflags correctly after writes to CONTROL

[Peter Maydell]

A write to the CONTROL register can change our current EL (by
writing to the nPRIV bit). That means that we can't assume
that s->current_el is still valid in trans_MSR_v7m() when
we try to rebuild the hflags.

Add a new helper rebuild_hflags_m32_newel() which, like the
existing rebuild_hflags_a32_newel(), recalculates the current
EL from scratch, and use it in trans_MSR_v7m().

This fixes an assertion about an hflags mismatch when the
guest changes privilege by writing to CONTROL.

Signed-off-by: Peter Maydell <address@hidden>
---
 target/arm/helper.h    |  1 +
 target/arm/helper.c    | 12 ++++++++++++
 target/arm/translate.c |  7 +++----
 3 files changed, 16 insertions(+), 4 deletions(-)

diff --git a/target/arm/helper.h b/target/arm/helper.h
index fcbf5041213..a63fd5dfb73 100644
--- a/target/arm/helper.h
+++ b/target/arm/helper.h
@@ -90,6 +90,7 @@ DEF_HELPER_4(msr_banked, void, env, i32, i32, i32)
 DEF_HELPER_2(get_user_reg, i32, env, i32)
 DEF_HELPER_3(set_user_reg, void, env, i32, i32)
 
+DEF_HELPER_FLAGS_1(rebuild_hflags_m32_newel, TCG_CALL_NO_RWG, void, env)
 DEF_HELPER_FLAGS_2(rebuild_hflags_m32, TCG_CALL_NO_RWG, void, env, int)
 DEF_HELPER_FLAGS_1(rebuild_hflags_a32_newel, TCG_CALL_NO_RWG, void, env)
 DEF_HELPER_FLAGS_2(rebuild_hflags_a32, TCG_CALL_NO_RWG, void, env, int)
diff --git a/target/arm/helper.c b/target/arm/helper.c
index 6be9ffa09ef..2eec812b80b 100644
--- a/target/arm/helper.c
+++ b/target/arm/helper.c
@@ -12325,6 +12325,18 @@ void arm_rebuild_hflags(CPUARMState *env)
     env->hflags = rebuild_hflags_internal(env);
 }
 
+/*
+ * If we have triggered a EL state change we can't rely on the
+ * translator having passed it to us, we need to recompute.
+ */
+void HELPER(rebuild_hflags_m32_newel)(CPUARMState *env)
+{
+    int el = arm_current_el(env);
+    int fp_el = fp_exception_el(env, el);
+    ARMMMUIdx mmu_idx = arm_mmu_idx_el(env, el);
+    env->hflags = rebuild_hflags_m32(env, fp_el, mmu_idx);
+}
+
 void HELPER(rebuild_hflags_m32)(CPUARMState *env, int el)
 {
     int fp_el = fp_exception_el(env, el);
diff --git a/target/arm/translate.c b/target/arm/translate.c
index 7f0154194cf..4715ca0d2ad 100644
--- a/target/arm/translate.c
+++ b/target/arm/translate.c
@@ -8551,7 +8551,7 @@ static bool trans_MRS_v7m(DisasContext *s, arg_MRS_v7m *a)
 
 static bool trans_MSR_v7m(DisasContext *s, arg_MSR_v7m *a)
 {
-    TCGv_i32 addr, reg, el;
+    TCGv_i32 addr, reg;
 
     if (!arm_dc_feature(s, ARM_FEATURE_M)) {
         return false;
@@ -8561,9 +8561,8 @@ static bool trans_MSR_v7m(DisasContext *s, arg_MSR_v7m *a)
     gen_helper_v7m_msr(cpu_env, addr, reg);
     tcg_temp_free_i32(addr);
     tcg_temp_free_i32(reg);
-    el = tcg_const_i32(s->current_el);
-    gen_helper_rebuild_hflags_m32(cpu_env, el);
-    tcg_temp_free_i32(el);
+    /* If we wrote to CONTROL, the EL might have changed */
+    gen_helper_rebuild_hflags_m32_newel(cpu_env);
     gen_lookup_tb(s);
     return true;
 }
-- 
2.20.1