target-arm: Implement SP_EL0, SP_EL1

Implement handling for the AArch64 SP_EL0 system register.
This holds the EL0 stack pointer, and is only accessible when
it's not being used as the stack pointer, ie when we're in EL1
and EL1 is using its own stack pointer. We also provide a
definition of the SP_EL1 register; this isn't guest visible
as a system register for an implementation like QEMU which
doesn't provide EL2 or EL3; however it is useful for ensuring
the underlying state is migrated.

We need to update the state fields in the CPU state whenever
we switch stack pointers; this happens when we take an exception
and also when SPSEL is used to change the bit in PSTATE which
indicates which stack pointer EL1 should use.

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Peter Crosthwaite <peter.crosthwaite@xilinx.com>

1 files changed, 34 insertions, 0 deletions

diff --git a/target-arm/helper.c b/target-arm/helper.c
index 276ecf2..27a3dc2 100644
--- a/target-arm/helper.c
+++ b/target-arm/helper.c
@@ -1783,6 +1783,27 @@ static uint64_t aa64_dczid_read(CPUARMState *env, const ARMCPRegInfo *ri)
     return cpu->dcz_blocksize | dzp_bit;
 }
 
+static CPAccessResult sp_el0_access(CPUARMState *env, const ARMCPRegInfo *ri)
+{
+    if (!env->pstate & PSTATE_SP) {
+        /* Access to SP_EL0 is undefined if it's being used as
+         * the stack pointer.
+         */
+        return CP_ACCESS_TRAP_UNCATEGORIZED;
+    }
+    return CP_ACCESS_OK;
+}
+
+static uint64_t spsel_read(CPUARMState *env, const ARMCPRegInfo *ri)
+{
+    return env->pstate & PSTATE_SP;
+}
+
+static void spsel_write(CPUARMState *env, const ARMCPRegInfo *ri, uint64_t val)
+{
+    update_spsel(env, val);
+}
+
 static const ARMCPRegInfo v8_cp_reginfo[] = {
     /* Minimal set of EL0-visible registers. This will need to be expanded
      * significantly for system emulation of AArch64 CPUs.
@@ -1915,6 +1936,19 @@ static const ARMCPRegInfo v8_cp_reginfo[] = {
       .type = ARM_CP_NO_MIGRATE,
       .opc0 = 3, .opc1 = 0, .crn = 4, .crm = 0, .opc2 = 1,
       .access = PL1_RW, .fieldoffset = offsetof(CPUARMState, elr_el1) },
+    /* We rely on the access checks not allowing the guest to write to the
+     * state field when SPSel indicates that it's being used as the stack
+     * pointer.
+     */
+    { .name = "SP_EL0", .state = ARM_CP_STATE_AA64,
+      .opc0 = 3, .opc1 = 0, .crn = 4, .crm = 1, .opc2 = 0,
+      .access = PL1_RW, .accessfn = sp_el0_access,
+      .type = ARM_CP_NO_MIGRATE,
+      .fieldoffset = offsetof(CPUARMState, sp_el[0]) },
+    { .name = "SPSel", .state = ARM_CP_STATE_AA64,
+      .opc0 = 3, .opc1 = 0, .crn = 4, .crm = 2, .opc2 = 0,
+      .type = ARM_CP_NO_MIGRATE,
+      .access = PL1_RW, .readfn = spsel_read, .writefn = spsel_write },
     REGINFO_SENTINEL
 };