esp_system: component init functions macro

Allows components to declare initialization function, such that the
startup code does not have direct dependency on the component.

components/esp32/ld/esp32.project.ld.in

@@ -208,6 +208,10 @@ SECTIONS
     _coredump_dram_end = ABSOLUTE(.);
     
     /* should be placed after coredump mapping */
+    _esp_system_init_fn_array_start = ABSOLUTE(.);
+    KEEP (*(SORT(.esp_system_init_fn) SORT(.esp_system_init_fn.*)))
+    _esp_system_init_fn_array_end = ABSOLUTE(.);
+
     mapping[dram0_data]
 
     _data_end = ABSOLUTE(.);
@@ -278,6 +282,7 @@ SECTIONS
 
     mapping[flash_rodata]
 
+
     *(.irom1.text) /* catch stray ICACHE_RODATA_ATTR */
     *(.gnu.linkonce.r.*)
     *(.rodata1)
@@ -297,6 +302,7 @@ SECTIONS
     __init_array_start = ABSOLUTE(.);
     KEEP (*(EXCLUDE_FILE (*crtend.* *crtbegin.*) .ctors SORT(.ctors.*)))
     __init_array_end = ABSOLUTE(.);
+
     KEEP (*crtbegin.*(.dtors))
     KEEP (*(EXCLUDE_FILE (*crtend.*) .dtors))
     KEEP (*(SORT(.dtors.*)))

components/esp32s2/ld/esp32s2.project.ld.in

@@ -214,6 +214,10 @@ SECTIONS
     _coredump_dram_end = ABSOLUTE(.);
     
     /* should be placed after coredump mapping */
+    _esp_system_init_fn_array_start = ABSOLUTE(.);
+    KEEP (*(SORT(.esp_system_init_fn) SORT(.esp_system_init_fn.*)))
+    _esp_system_init_fn_array_end = ABSOLUTE(.);
+
     mapping[dram0_data]
 
     _data_end = ABSOLUTE(.);

components/esp_system/private_include/startup_internal.h

@@ -0,0 +1,37 @@
+// Copyright 2015-2018 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.
+
+#pragma once
+
+#include "esp_attr.h"
+typedef struct {
+  void (*fn)(void);
+  uint32_t cores;
+} esp_system_init_fn_t;
+
+/*
+ * Declare an component initialization function that will execute on the specified cores (ex. if BIT0 == 1, will execute
+ * on CORE0, CORE1 if BIT1 and so on).
+ * 
+ * @note Initialization functions should be placed in a compilation unit where at least one other
+ * symbol is referenced 'meaningfully' in another compilation unit, otherwise this gets discarded during linking. (By
+ * 'meaningfully' we mean the reference should not itself get optimized out by the compiler/discarded by the linker).
+ */
+#define ESP_SYSTEM_INIT_FN(f, c, ...) \
+static void  __attribute__((used)) __VA_ARGS__ __esp_system_init_fn_##f(void); \
+static __attribute__((used)) esp_system_init_fn_t _SECTION_ATTR_IMPL(".esp_system_init_fn", f) \
+                    esp_system_init_fn_##f = { .fn = ( __esp_system_init_fn_##f), .cores = (c) }; \
+static __attribute__((used)) __VA_ARGS__ void __esp_system_init_fn_##f(void) // [refactor-todo] this can be made public API if we allow components to declare init functions, 
+                                                                             // instead of calling them explicitly
+

components/esp_system/startup.c

@@ -97,6 +97,20 @@ static void do_global_ctors(void)
     }
 }
 
+static void do_system_init_fn(void)
+{
+    extern esp_system_init_fn_t _esp_system_init_fn_array_start;
+    extern esp_system_init_fn_t _esp_system_init_fn_array_end;
+
+    esp_system_init_fn_t *p;
+
+    for (p = &_esp_system_init_fn_array_end - 1; p >= &_esp_system_init_fn_array_start; --p) {
+        if (p->cores & BIT(cpu_hal_get_core_id())) {
+            (*(p->fn))();
+        }
+    }
+}
+
 static void main_task(void* args)
 {
 #if !CONFIG_FREERTOS_UNICORE
@@ -312,6 +326,7 @@ void IRAM_ATTR start_cpu0_default(void)
     esp_dport_access_int_init();
 #endif
 
+
     spi_flash_init();
     /* init default OS-aware flash access critical section */
     spi_flash_guard_set(&g_flash_guard_default_ops);
@@ -345,6 +360,8 @@ void IRAM_ATTR start_cpu0_default(void)
 #endif
 #endif
 
+    do_system_init_fn();
+
     portBASE_TYPE res = xTaskCreatePinnedToCore(&main_task, "main",
                                                 ESP_TASK_MAIN_STACK, NULL,
                                                 ESP_TASK_MAIN_PRIO, NULL, 0);