fix(bootloader_hooks): Fix log_v2 support in bootloader hooks

Closes https://github.com/espressif/esp-idf/issues/18482

components/esp_rom/patches/esp_rom_sys.c

@@ -1,5 +1,5 @@
 /*
- * SPDX-FileCopyrightText: 2010-2025 Espressif Systems (Shanghai) CO LTD
+ * SPDX-FileCopyrightText: 2010-2026 Espressif Systems (Shanghai) CO LTD
  *
  * SPDX-License-Identifier: Apache-2.0
  */
@@ -29,8 +29,18 @@ void esp_rom_output_putc(char c)
 #endif // !ESP_ROM_HAS_OUTPUT_PUTC_FUNC
 
 #if !ESP_ROM_HAS_OUTPUT_TO_CHANNELS_FUNC
+static void esp_rom_output_noop(char c)
+{
+    (void)c;
+}
+
 void (* _putc1)(char c) = esp_rom_output_putc;
-void (* _putc2)(char c) = NULL;
+/* Initialize _putc2 to a noop function (not NULL) so it is safe to call even before
+ * bootloader BSS is cleared, e.g. from bootloader hooks (bootloader_before_init).
+ * In log_v2, ESP_LOG routes output through esp_rom_output_to_channels() which calls
+ * _putc2 directly. If _putc2 were NULL or uninitialised at that point, it would crash.
+ * Channel 2 output is disabled later (set to NULL) once startup determines it is unused. */
+void (* _putc2)(char c) = esp_rom_output_noop;
 
 void esp_rom_output_to_channels(char c)
 {

examples/custom_bootloader/bootloader_hooks/bootloader_components/my_boot_hooks/hooks.c

@@ -8,9 +8,10 @@ void bootloader_hooks_include(void){
 
 
 void bootloader_before_init(void) {
-    /* Keep in my mind that a lot of functions cannot be called from here
+    /* Keep in mind that a lot of functions cannot be called from here
      * as system initialization has not been performed yet, including
-     * BSS, SPI flash, or memory protection. */
+     * BSS, SPI flash, or memory protection.
+     */
     ESP_LOGI("HOOK", "This hook is called BEFORE bootloader initialization");
 }
 

examples/custom_bootloader/bootloader_hooks/pytest_custom_bootloader_hooks.py

@@ -1,4 +1,4 @@
-# SPDX-FileCopyrightText: 2021-2025 Espressif Systems (Shanghai) CO LTD
+# SPDX-FileCopyrightText: 2021-2026 Espressif Systems (Shanghai) CO LTD
 # SPDX-License-Identifier: CC0-1.0
 import pytest
 from pytest_embedded import Dut
@@ -6,6 +6,17 @@ from pytest_embedded_idf.utils import idf_parametrize
 
 
 @pytest.mark.generic
+@pytest.mark.parametrize(
+    'config',
+    [
+        'default',
+        # log_v2 routes ESP_LOG through esp_rom_output_to_channels() -> _putc2. This config
+        # verifies that logging works correctly in bootloader hooks (before BSS is cleared),
+        # where _putc2 must be initialized to a safe noop rather than left as NULL/garbage.
+        'log_v2',
+    ],
+    indirect=True,
+)
 @idf_parametrize('target', ['esp32s3', 'esp32c3'], indirect=['target'])
 def test_custom_bootloader_hooks_example(dut: Dut) -> None:
     # Expect to read both hooks messages

examples/custom_bootloader/bootloader_hooks/sdkconfig.ci.default

@@ -0,0 +1 @@
+# This is left intentionally blank. It inherits all configurations from sdkconfig.defaults.

examples/custom_bootloader/bootloader_hooks/sdkconfig.ci.log_v2

@@ -0,0 +1,2 @@
+CONFIG_LOG_VERSION_2=y
+CONFIG_ESPTOOLPY_FLASHSIZE_4MB=y