bootloader_support: don't check signature when JTAG is attached

If an insecure configuration is enabled (no hardware secure boot, just
software signature check), skip the signature check in bootloader if
JTAG debugger is attached. This allows the debugger to set breakpoints
in Flash before the application runs.

Closes https://github.com/espressif/esp-idf/issues/4734
Closes https://github.com/espressif/esp-idf/issues/4878

components/bootloader_support/src/esp_image_format.c

@@ -220,8 +220,17 @@ static esp_err_t image_load(esp_image_load_mode_t mode, const esp_partition_pos_
 
 #ifdef SECURE_BOOT_CHECK_SIGNATURE
             // secure boot images have a signature appended
-            err = verify_secure_boot_signature(sha_handle, data, image_digest, verified_digest);
-#else
+#if defined(BOOTLOADER_BUILD) && !defined(CONFIG_SECURE_BOOT)
+            // If secure boot is not enabled in hardware, then
+            // skip the signature check in bootloader when the debugger is attached.
+            // This is done to allow for breakpoints in Flash.
+            if (!esp_cpu_in_ocd_debug_mode()) {
+#else // CONFIG_SECURE_BOOT
+            if (true) {
+#endif // end checking for JTAG
+                err = verify_secure_boot_signature(sha_handle, data, image_digest, verified_digest);
+            }
+#else // SECURE_BOOT_CHECK_SIGNATURE
             // No secure boot, but SHA-256 can be appended for basic corruption detection
             if (sha_handle != NULL && !esp_cpu_in_ocd_debug_mode()) {
                 err = verify_simple_hash(sha_handle, data);