target/arm: Hyp mode R14 is shared with User and System

Hyp mode is an exception to the general rule that each AArch32
mode has its own r13, r14 and SPSR -- it has a banked r13 and
SPSR but shares its r14 with User and System mode. We were
incorrectly implementing it as banked, which meant that on
entry to Hyp mode r14 was 0 rather than the USR/SYS r14.

We provide a new function r14_bank_number() which is like
the existing bank_number() but provides the index into
env->banked_r14[]; bank_number() provides the index to use
for env->banked_r13[] and env->banked_cpsr[].

All the points in the code that were using bank_number()
to index into env->banked_r14[] are updated for consintency:
 * switch_mode() -- this is the only place where we fix
   an actual bug
 * aarch64_sync_32_to_64() and aarch64_sync_64_to_32():
   no behavioural change as we already special-cased Hyp R14
 * kvm32.c: no behavioural change since the guest can't ever
   be in Hyp mode, but conceptually the right thing to do
 * msr_banked()/mrs_banked(): we can never get to the case
   that accesses banked_r14[] with tgtmode == ARM_CPU_MODE_HYP,
   so no behavioural change

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
Reviewed-by: Edgar E. Iglesias <edgar.iglesias@xilinx.com>
Reviewed-by: Alex Bennée <alex.bennee@linaro.org>
Message-id: 20181109173553.22341-2-peter.maydell@linaro.org

1 files changed, 16 insertions, 0 deletions

diff --git a/target/arm/internals.h b/target/arm/internals.h
index a32d359dd0..d208b70a64 100644
--- a/target/arm/internals.h
+++ b/target/arm/internals.h
@@ -145,6 +145,22 @@ static inline int bank_number(int mode)
     g_assert_not_reached();
 }
 
+/**
+ * r14_bank_number: Map CPU mode onto register bank for r14
+ *
+ * Given an AArch32 CPU mode, return the index into the saved register
+ * banks to use for the R14 (LR) in that mode. This is the same as
+ * bank_number(), except for the special case of Hyp mode, where
+ * R14 is shared with USR and SYS, unlike its R13 and SPSR.
+ * This should be used as the index into env->banked_r14[], and
+ * bank_number() used for the index into env->banked_r13[] and
+ * env->banked_spsr[].
+ */
+static inline int r14_bank_number(int mode)
+{
+    return (mode == ARM_CPU_MODE_HYP) ? BANK_USRSYS : bank_number(mode);
+}
+
 void arm_cpu_register_gdb_regs_for_features(ARMCPU *cpu);
 void arm_translate_init(void);