Linker script: insert absolute address of the function to the generated code

Question

I have a question related to gcc\'s linker.

I\'m working with embedded stuff (PIC32), but PIC32\'s compiler and linker are based on gcc, so, main things should be co

Answer 1

The way I found around this was to use function pointers, i.e.

void (*formatted_write)( int a, char * b, struct mystruct c );

then, in the code somewhere at boot set the address of this function, i.e.

formatted_write = 0xa0000;

you can then call your function using the normal convention.

Additionally, you can use the -Wl,--just-symbols=symbols.txt flag when compiling. You can set the address of your symbols as follows:

formatted_write = 0xa0000;

Answer 2

For the case that someone has the same problem (like me some hours ago), there is a still better solution:

Let "bootloader.out" be the bootloader-binary. Then we can generate with

nm -g bootloader.out | grep '^[0-9,a-e]\{8\} T' | awk '{printf "PROVIDE(%s = 0x%s);\n",$3,$1}' > bootloader.inc

a file that we can include in the linker script of the application with

INCLUDE bootloader.inc

The linker knows now the addresses of all bootloader-functions and we can link against it without to have the actual function code in the application. All what we need there is a declaration for every bootloader-function which we want to execute.