bsps/aarch64: Customize EL2/EL3 start support

Make the support for starting in EL2/EL3 customizable.  A boot loader or
the Arm Trusted Firmware should start RTEMS in non-secure EL1 mode.

In start.S, use local labels.

For the aarch64/xilinx-zynqmp the support for starting in EL2/EL3 is
disabled by default.  For the Qemu xlnx-zcu102 machine, the default is
to start in non-secure EL1 mode.  This can be controlled by options, for
example "-machine xlnx-zcu102,secure=on,virtualization=on".

bsps/aarch64/a53/start/bspstarthooks.c

@@ -37,10 +37,12 @@
 #include <bsp.h>
 #include <bsp/start.h>
 
+#ifdef BSP_START_ENABLE_EL3_START_SUPPORT
 BSP_START_TEXT_SECTION void bsp_start_hook_0(void)
 {
   /* Do nothing */
 }
+#endif
 
 BSP_START_TEXT_SECTION void bsp_start_hook_1(void)
 {

bsps/aarch64/a72/start/bspstarthooks.c

@@ -37,10 +37,12 @@
 #include <bsp.h>
 #include <bsp/start.h>
 
+#ifdef BSP_START_ENABLE_EL3_START_SUPPORT
 BSP_START_TEXT_SECTION void bsp_start_hook_0(void)
 {
   /* Do nothing */
 }
+#endif
 
 BSP_START_TEXT_SECTION void bsp_start_hook_1(void)
 {

bsps/aarch64/raspberrypi/start/bspstarthooks.c

@@ -39,10 +39,12 @@
 #include <bsp/start.h>
 #include <rtems/score/cpu.h>
 
+#ifdef BSP_START_ENABLE_EL3_START_SUPPORT
 BSP_START_TEXT_SECTION void bsp_start_hook_0(void)
 {
   /* Do nothing */
 }
+#endif
 
 BSP_START_TEXT_SECTION void bsp_start_hook_1(void)
 {
@@ -50,4 +52,4 @@ BSP_START_TEXT_SECTION void bsp_start_hook_1(void)
   bsp_start_copy_sections();
   raspberrypi_4_setup_mmu_and_cache();
   bsp_start_clear_bss();
-}
+}

bsps/aarch64/shared/start/start.S

@@ -137,13 +137,18 @@ _start:
 #endif
   msr SCTLR_EL1, x0
 
+#if defined(BSP_START_ENABLE_EL2_START_SUPPORT) || \
+  defined(BSP_START_ENABLE_EL3_START_SUPPORT)
   mrs x0, CurrentEL
   cmp x0, #(1<<2)
-  b.eq _el1_start
-  cmp x0, #(2<<2)
-  b.eq _el2_start
+  b.eq .L_el1_start
+#endif
 
-_el3_start:
+#if defined(BSP_START_ENABLE_EL3_START_SUPPORT)
+  cmp x0, #(2<<2)
+  b.eq .L_el2_start
+
+.L_el3_start:
   /*
    * Before leaving the Secure World, we need to initialize the GIC. We
    * do that here in an early stack context in EL3. This will NOT work
@@ -189,11 +194,14 @@ _el3_start:
   msr SPSR_EL3, x0
 
   /* Set EL2 entry point */
-  adr x0, _el2_start
+  adr x0, .L_el2_start
   msr ELR_EL3, x0
   eret
+#endif
 
-_el2_start:
+#if defined(BSP_START_ENABLE_EL2_START_SUPPORT) || \
+  defined(BSP_START_ENABLE_EL3_START_SUPPORT)
+.L_el2_start:
   /* Drop from EL2 to EL1 */
 
   /* Configure HCR_EL2 */
@@ -212,11 +220,12 @@ _el2_start:
   msr SPSR_EL2, x0
 
   /* Set EL1 entry point */
-  adr x0, _el1_start
+  adr x0, .L_el1_start
   msr ELR_EL2, x0
   eret
 
-_el1_start:
+.L_el1_start:
+#endif
 
 #ifdef RTEMS_SMP
   bl _AArch64_Get_current_processor_for_system_start

bsps/aarch64/xilinx-versal/start/bspstarthooks.c

@@ -38,10 +38,12 @@
 #include <bsp/irq-generic.h>
 #include <bsp/start.h>
 
+#ifdef BSP_START_ENABLE_EL3_START_SUPPORT
 BSP_START_TEXT_SECTION void bsp_start_hook_0(void)
 {
   bsp_interrupt_facility_initialize();
 }
+#endif
 
 BSP_START_TEXT_SECTION void bsp_start_hook_1(void)
 {

bsps/aarch64/xilinx-zynqmp/start/bspstarthooks.c

@@ -45,10 +45,12 @@
 #include <bsp/irq-generic.h>
 #endif
 
+#ifdef BSP_START_ENABLE_EL3_START_SUPPORT
 BSP_START_TEXT_SECTION void bsp_start_hook_0( void )
 {
   /* do nothing */
 }
+#endif
 
 BSP_START_TEXT_SECTION void bsp_start_hook_1( void )
 {

spec/build/bsps/aarch64/optstartel2.yml

@@ -0,0 +1,18 @@
+SPDX-License-Identifier: CC-BY-SA-4.0 OR BSD-2-Clause
+actions:
+- get-boolean: null
+- define-condition: null
+build-type: option
+copyrights:
+- Copyright (C) 2024 embedded brains GmbH & Co. KG
+default:
+- enabled-by: true
+  value: true
+description: |
+  If this option is defined, then starting the system in exception level 2
+  (EL2) is supported.
+enabled-by: true
+format: '{}'
+links: []
+name: BSP_START_ENABLE_EL2_START_SUPPORT
+type: build

spec/build/bsps/aarch64/optstartel3.yml

@@ -0,0 +1,20 @@
+SPDX-License-Identifier: CC-BY-SA-4.0 OR BSD-2-Clause
+actions:
+- get-boolean: null
+- define-condition: null
+build-type: option
+copyrights:
+- Copyright (C) 2024 embedded brains GmbH & Co. KG
+default:
+- enabled-by: bsps/aarch64/xilinx-zynqmp
+  value: false
+- enabled-by: true
+  value: true
+description: |
+  If this option is defined, then starting the system in exception level 3
+  (EL3) is supported.
+enabled-by: true
+format: '{}'
+links: []
+name: BSP_START_ENABLE_EL3_START_SUPPORT
+type: build

spec/build/bsps/aarch64/start.yml

@@ -7,7 +7,11 @@ cppflags: []
 enabled-by: true
 includes: []
 install-path: ${BSP_LIBDIR}
-links: []
+links:
+- role: build-dependency
+  uid: optstartel2
+- role: build-dependency
+  uid: optstartel3
 source:
 - bsps/aarch64/shared/start/start.S
 target: start.o