target/arm: fix CBAR register for AArch64 CPUs

For AArch64 CPUs with a CBAR register, we have two views for it:
  - in AArch64 state, the CBAR_EL1 register (S3_1_C15_C3_0), returns the
    full 64 bits CBAR value
  - in AArch32 state, the CBAR register (cp15, opc1=1, CRn=15, CRm=3, opc2=0)
    returns a 32 bits view such that:
      CBAR = CBAR_EL1[31:18] 0..0 CBAR_EL1[43:32]

This commit fixes the current implementation where:
  - CBAR_EL1 was returning the 32 bits view instead of the full 64 bits
    value,
  - CBAR was returning a truncated 32 bits version of the full 64 bits
    one, instead of the 32 bits view
  - CBAR was declared as cp15, opc1=4, CRn=15, CRm=0, opc2=0, which is
    the CBAR register found in the ARMv7 Cortex-Ax CPUs, but not in
    ARMv8 CPUs.

Signed-off-by: Luc Michel <luc.michel@greensocs.com>
Message-id: 20190912110103.1417887-1-luc.michel@greensocs.com
[PMM: Added a comment about the two different kinds of CBAR]
Reviewed-by: Peter Maydell <peter.maydell@linaro.org>
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>

1 files changed, 16 insertions, 3 deletions

diff --git a/target/arm/helper.c b/target/arm/helper.c
index 507026c915..bc1130d989 100644
--- a/target/arm/helper.c
+++ b/target/arm/helper.c
@@ -6733,6 +6733,19 @@ void register_cp_regs_for_features(ARMCPU *cpu)
     }
 
     if (arm_feature(env, ARM_FEATURE_CBAR)) {
+        /*
+         * CBAR is IMPDEF, but common on Arm Cortex-A implementations.
+         * There are two flavours:
+         *  (1) older 32-bit only cores have a simple 32-bit CBAR
+         *  (2) 64-bit cores have a 64-bit CBAR visible to AArch64, plus a
+         *      32-bit register visible to AArch32 at a different encoding
+         *      to the "flavour 1" register and with the bits rearranged to
+         *      be able to squash a 64-bit address into the 32-bit view.
+         * We distinguish the two via the ARM_FEATURE_AARCH64 flag, but
+         * in future if we support AArch32-only configs of some of the
+         * AArch64 cores we might need to add a specific feature flag
+         * to indicate cores with "flavour 2" CBAR.
+         */
         if (arm_feature(env, ARM_FEATURE_AARCH64)) {
             /* 32 bit view is [31:18] 0...0 [43:32]. */
             uint32_t cbar32 = (extract64(cpu->reset_cbar, 18, 14) << 18)
@@ -6740,12 +6753,12 @@ void register_cp_regs_for_features(ARMCPU *cpu)
             ARMCPRegInfo cbar_reginfo[] = {
                 { .name = "CBAR",
                   .type = ARM_CP_CONST,
-                  .cp = 15, .crn = 15, .crm = 0, .opc1 = 4, .opc2 = 0,
-                  .access = PL1_R, .resetvalue = cpu->reset_cbar },
+                  .cp = 15, .crn = 15, .crm = 3, .opc1 = 1, .opc2 = 0,
+                  .access = PL1_R, .resetvalue = cbar32 },
                 { .name = "CBAR_EL1", .state = ARM_CP_STATE_AA64,
                   .type = ARM_CP_CONST,
                   .opc0 = 3, .opc1 = 1, .crn = 15, .crm = 3, .opc2 = 0,
-                  .access = PL1_R, .resetvalue = cbar32 },
+                  .access = PL1_R, .resetvalue = cpu->reset_cbar },
                 REGINFO_SENTINEL
             };
             /* We don't implement a r/w 64 bit CBAR currently */