CODEWITHSUNDEEP
gccattributesarm
zhang wenjin
zhang wenjin

Reputation: 11

How to keep unused function in firmware image use arm-none-eabi-gcc toolchain?

I now try create a firmware image running STM32F0xx MCU. It's like flash algorithm, provide some function call to control STM32F0xx MCU Pins, but it's more complicated than flash algorithm. So it will use STM32 HAL lib and Mbed lib.

The Compiler/linker use "-ffunction-sections" and "-fdata-sections" flags.

So I use "attribute((used))" to try keep function into firmware image, but it's failed.
arm-none-eabi-gcc toolchain version is 4.9.3.

My codes like this:

extern "C" {
__attribute__((__used__))  void writeSPI(uint32_t value)
{
    for (int i = 0; i < spiPinsNum; i++) {
        spiPins[i] = (((value >> i) & 0x01) != 0) ? 1 : 0;
    }
    __ASM volatile ("movs r0, #0"); // set R0 to 0 show success
    __ASM volatile ("bkpt  #0");   // halt MCU
}

}

After build succeed, the writeSPI symbol no in image. I also try static for function, the "-uXXXXX" flag, create a new section.

Question: How keep writeSPI function code with "-ffunction-sections" and "-fdata-sections" flags?

Upvotes: 1

Views: 1514

Answers (1)

Andy Brown
Andy Brown

Reputation: 13009

One way to ensure a wanted function doesn't get garbage collected is to create a function pointer to it within a method that is used. You don't have to do anything with the function pointer, just initialize it.

void(*dummy)(uint32_t)=&writeSPI;

An alternative would be to omit the -ffunction-sections flag from the compilation units that contain functions that should not be stripped, but that may involve significant restructuring of your code base.

Upvotes: 0

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