ESP32 Forum

Posted: **Sun May 26, 2019 5:26 pm**

I am trying to find a way to execute code (for exemple, load a code from SD card to RAM) without re-flashing esp32. I know ESP32 can execute instructions from IRAM, but when I try to do it, esp32 crashes.

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int main()
{
    int c = 0;
    for (int i = 0; i < 1000; i ++)
    {
        for (int j = 0; j < 1000; j ++)
        {
            c++;
        }
    }
}

This is the code (the compiled binary) I am trying to execute from IRAM. I am compiling it with the following linker script:

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SECTIONS
{
	.literal : {*(.literal)}
	.text : {*(.text)}
}

I compile the code using

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xtensa-esp32-elf-gcc.exe -Xlinker -T link.ld -std=c99 -Os -nostdlib -c main.c -o out/main.o
xtensa-esp32-elf-objcopy -O binary out/main.o out/APP.bin

This is the output binary:

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0x36, 0x41, 0x00, 0x0C, 0x02, 0x1D, 0xF0

The code I am using on ESP32:

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#include <stdio.h>
#include "freertos/FreeRTOS.h"
#include "freertos/task.h"
#include "esp_system.h"
#include "esp_attr.h"

#define SIZE 7
IRAM_ATTR uint32_t PROGRAM[SIZE] = {
0x36, 0x41, 0x00, 0x0C, 0x02, 0x1D, 0xF0
};

const void* PTR = (void*)PROGRAM;

void exec_bin()
{
  typedef void func(void);
  func* f = (func*)(PTR);
  printf("\nIT'S NOW ...\n");
  f(); // ESP32 CRASHES HERE <<---

}

void app_main()
{
  printf("\n\nGoint to exec code ...\n\n");
  vTaskDelay(1000 / portTICK_RATE_MS);

  exec_bin();

  printf("Done");
}

I put the compiled binary on IRAM using IRAM_ATTR. This code basically tryies to execute the compiled binary from IRAM, but when I call f() esp32 crashes.

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Guru Meditation Error: Core  0 panic'ed (Unhandled debug exception)
Debug exception reason: BREAK instr

What am I doing wrong?
* Sorry for my english. I speak portuguese. This is the first time I use this forum.

Posted: **Sun May 26, 2019 11:56 pm**

Hi isaque,

Your short binary code looks like it should probably run.

- If you capture both the full output of the panic handler (registers) and also print the address of f() before you call it, how does the PC address in the panic handler compare with the address of f()? Is it definitely crashing inside f()?

- This doesn't explain why it's crashing, but it looks like the optimizer has removed all the code in main.c - the disassembly looks like it will be "entry a1, 32; movi a2, 0; retw.n" - ie "return 0". You can run "xtensa-esp32-elf-objdump -S main.o" to compare.

- This also doesn't explain why it's crashing, but FWIW the program in main.o is not linked - main.o is unlinked object code. The "-c" option for gcc means "don't run the linker" so the linker options are being ignored. This probably doesn't matter in this case because the function doesn't link against any other objects, but it will start to matter if you write more complex code.

Posted: **Mon May 27, 2019 8:08 am**

Your function pointer might be pointing to literal instead of text? Maybe not since the constant is less than 12 bits and the code is mostly optimised away, but that is all I had to do I think.

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