bootloader: override the 2nd stage bootloader

Add the possibility to have user bootloader components. This is performed
from an application/project, by creating bootloader components. To do so,
it is required to create a `bootloader_component` directory containing
the custom modules to be compiled with the bootloader.

Thanks to this, two solutions are available to override the bootloader now:
- Using hooks within a user bootloader component
- Using a user defined `main` bootloader component to totally override the
  old implementation

Please check the two new examples in `examples/custom_bootloader`

* Closes https://github.com/espressif/esp-idf/issues/7043

components/bootloader/Makefile.projbuild

@@ -27,6 +27,9 @@ BOOTLOADER_OFFSET := 0x1000
 # NB: Some variables are cleared in the environment, not
 # overriden, because they need to be re-defined in the child
 # project.
+#
+# Pass PROJECT_PATH variable, it will let the subproject look
+# for user defined bootloader component(s).
 BOOTLOADER_MAKE= +\
 	PROJECT_PATH= \
 	COMPONENT_DIRS= \
@@ -35,7 +38,8 @@ BOOTLOADER_MAKE= +\
 	BUILD_DIR_BASE=$(BOOTLOADER_BUILD_DIR) \
 	TEST_COMPONENTS= \
 	TESTS_ALL= \
-	EXCLUDE_COMPONENTS=
+	EXCLUDE_COMPONENTS= \
+	PROJECT_SOURCE_DIR=$(PROJECT_PATH)
 
 .PHONY: bootloader-clean bootloader-flash bootloader-list-components bootloader $(BOOTLOADER_BIN)
 

components/bootloader/project_include.cmake

@@ -117,6 +117,7 @@ externalproject_add(bootloader
     CMAKE_ARGS  -DSDKCONFIG=${sdkconfig} -DIDF_PATH=${idf_path} -DIDF_TARGET=${idf_target}
                 -DPYTHON_DEPS_CHECKED=1 -DPYTHON=${python}
                 -DEXTRA_COMPONENT_DIRS=${CMAKE_CURRENT_LIST_DIR}
+                -DPROJECT_SOURCE_DIR=${PROJECT_SOURCE_DIR}
                 ${sign_key_arg} ${ver_key_arg}
                 # LEGACY_INCLUDE_COMMON_HEADERS has to be passed in via cache variable since
                 # the bootloader common component requirements depends on this and

components/bootloader/subproject/CMakeLists.txt

@@ -33,6 +33,21 @@ set(COMPONENTS
     efuse
     esp_system
     newlib)
+
+# Make EXTRA_COMPONENT_DIRS variable to point to the bootloader_components directory
+# of the project being compiled
+set(PROJECT_EXTRA_COMPONENTS "${PROJECT_SOURCE_DIR}/bootloader_components")
+set(EXTRA_COMPONENT_DIRS "${PROJECT_EXTRA_COMPONENTS}" APPEND)
+
+# Consider each directory in project's bootloader_components as a component to be compiled
+file(GLOB proj_components RELATIVE ${PROJECT_EXTRA_COMPONENTS} ${PROJECT_EXTRA_COMPONENTS}/*)
+foreach(component ${proj_components})
+  # Only directories are considered as components
+  if(IS_DIRECTORY ${curdir}/${child})
+    list(APPEND COMPONENTS ${component})
+  endif()
+endforeach()
+
 set(BOOTLOADER_BUILD 1)
 include("${IDF_PATH}/tools/cmake/project.cmake")
 set(common_req log esp_rom esp_common esp_hw_support hal newlib)

components/bootloader/subproject/main/CMakeLists.txt

@@ -4,8 +4,10 @@ idf_component_register(SRCS "bootloader_start.c"
 idf_build_get_property(target IDF_TARGET)
 set(scripts "ld/${target}/bootloader.ld")
 
-if(NOT CONFIG_IDF_TARGET_ESP32C3 AND NOT CONFIG_IDF_TARGET_ESP32H2)
+if(NOT CONFIG_IDF_TARGET_ESP32H2)
     list(APPEND scripts "ld/${target}/bootloader.rom.ld")
 endif()
 
 target_linker_script(${COMPONENT_LIB} INTERFACE "${scripts}")
+
+target_link_libraries(${COMPONENT_LIB} INTERFACE "-u bootloader_hooks_include")

components/bootloader/subproject/main/bootloader_hooks.h

@@ -0,0 +1,38 @@
+// Copyright 2015-2021 Espressif Systems (Shanghai) PTE LTD
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+#ifndef BOOTLOADER_HOOKS_H
+#define BOOTLOADER_HOOKS_H
+
+/**
+ * @file The 2nd stage bootloader can be overriden or completed by an application.
+ * The functions declared here are weak, and thus, are meant to be defined by a user
+ * project, if required.
+ * Please check `custom_bootloader` ESP-IDF examples for more details about this feature.
+ */
+
+
+/**
+ * @brief Function executed *before* the second stage bootloader initialization,
+ * if provided.
+ */
+void __attribute__((weak)) bootloader_before_init(void);
+
+/**
+ * @brief Function executed *after* the second stage bootloader initialization,
+ * if provided.
+ */
+void __attribute__((weak)) bootloader_after_init(void);
+
+#endif // BOOTLOADER_HOOKS_H

components/bootloader/subproject/main/bootloader_start.c

@@ -16,6 +16,7 @@
 #include "bootloader_init.h"
 #include "bootloader_utility.h"
 #include "bootloader_common.h"
+#include "bootloader_hooks.h"
 
 static const char *TAG = "boot";
 
@@ -29,11 +30,21 @@ static int selected_boot_partition(const bootloader_state_t *bs);
  */
 void __attribute__((noreturn)) call_start_cpu0(void)
 {
+    // (0. Call the before-init hook, if available)
+    if (bootloader_before_init) {
+        bootloader_before_init();
+    }
+
     // 1. Hardware initialization
     if (bootloader_init() != ESP_OK) {
         bootloader_reset();
     }
 
+    // (1.1 Call the after-init hook, if available)
+    if (bootloader_after_init) {
+        bootloader_after_init();
+    }
+
 #ifdef CONFIG_BOOTLOADER_SKIP_VALIDATE_IN_DEEP_SLEEP
     // If this boot is a wake up from the deep sleep then go to the short way,
     // try to load the application which worked before deep sleep.

components/bootloader/subproject/main/ld/esp32c3/bootloader.rom.ld

@@ -0,0 +1 @@
+/* No definition for ESP32-C3 target */