target/arm: Recalculate hflags correctly after writes to CONTROL

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 <peter.maydell@linaro.org>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Message-id: 20200303174950.3298-4-peter.maydell@linaro.org
diff --git a/target/arm/helper.h b/target/arm/helper.h
index 72eb9e6..f37b867 100644
--- a/target/arm/helper.h
+++ b/target/arm/helper.h
@@ -90,6 +90,7 @@
 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)