ESP32 Forum

Hi everyone,

I’m planning to use the .rodata_custom_desc dedicated memory section to store basic device information. The goal is to allow a third-party software to read the generated .bin and identify this information.

Following the Espressif official documentation, I implemented the following:

typedef struct custom_app {
const char *my_custom_text;
} esp_custom_app_desc_t;

const __attribute__((section(".rodata_custom_desc"))) esp_custom_app_desc_t custom_app_desc = {
.my_custom_text = "Hello World 123",
};


The custom_app_desc is placed in main.c just to speed up testing.

I also ensured that the following line is added to the CMakeLists.txt of main.c:

target_link_libraries(${COMPONENT_TARGET} "-u custom_app_desc")


Result:
I can find the "Hello World 123" string in the generated .bin file, but not at the offset expected according to the Espressif documentation.

Question:
Is there something wrong with my setup, or am I misunderstanding how the .rodata_custom_desc section should be used?
Any suggestions would be greatly appreciated.


IDF version: 5.3.1

I can find the "Hello World 123" string in the generated .bin file, but not at the offset expected according to the Espressif documentation.

At what offset did you expect to find the string? According to what documentation?

As you don't specify a section to place the string literal in, it should end up in some .rodata section.

Try something like this:

I can find the "Hello World 123" string in the generated .bin file, but not at the offset expected according to the Espressif documentation.

At what offset did you expect to find the string? According to what documentation?

As you don't specify a section to place the string literal in, it should end up in some .rodata section.

Hello, thanks for reply.

https://docs.espressif.com/projects/esp ... -reference

"Offset for custom structure is sizeof(esp_image_header_t) + sizeof(esp_image_segment_header_t) + sizeof(esp_app_desc_t)."

I was expecting to see something within the first 100 bytes, but it's placed at 0x3000 +

The custom structure offset is 0x120 = (sizeof(esp_image_header_t) + sizeof(esp_image_segment_header_t) + sizeof(esp_app_desc_t)).
I double-checked it; it is exactly at 0x120 from the start of the app binary. I do not see an issue with it. If you use `const char *my_custom_text`, then yes, the text itself will be placed at +0x3000 offset. Just make sure that you use the correct type `const char my_custom_text[32]`.

If you are still getting this issue, please provide a simple example that demonstrates it.

Hello everyone.

const char my_custom_text[32] instead of const char *my_custom_text has moved from the 0x3000+ range to 0x120.

Thank you all for your support.