Linker Double Redirect (IAR EWARM)

Question

I have an IAR STM32 project where I am need to wrap a library function with some custom logic. I do not have the ability to recompile the library itself, so what I would like to do is create a function libfunction_shim that calls into the original libfunction. Using the --redirect linker option (--redirect libfunction=libfunction_shim), I can redirect calls to the original function to the shim, including calls inside the library itself. However, I need to call the original function from the shim.

If I add another redirect (--redirect libfunction_original=libfunction), it ends up redirecting libfunction_original to libfunction_shim, rather than the original libfunction. I've tried reordering the redirects, but it does the same thing regardless of order.

The linker log demonstrates this:

Symbol                     Redirected to          Reason        
-------------              ------                 ------
...
libfunction                libfunction_shim       command line  
libfunction_original       libfunction_shim       command line

What I would like this:

Symbol                     Redirected to          Reason        
-------------              ------                 ------
...
libfunction                libfunction_shim       command line  
libfunction_original       libfunction            command line

Is it possible to do this using the linker?

Why do you have to do this at linker level? In the other words, why not just call libfunction_shim at user code directly, or rename function using the preprocessor? — user694733
I need to redirect function calls internal to the library, as well. — GregoryComer

Johan Johan · Accepted Answer · 2019-06-03T08:14:51

This is not possible using linker redirects, you have to write your shim function in a specific way. A complete description is available in the manual (pg 225 in the 8.40.1 version) but to summarize: First you name the shim $sub$$libfunction, where libfunction is the name of the function to shadow. From inside the shim you can use $super$$libfunction to call the original version of libfunction. A minimal example is shown below.

extern void $Super$$foo(void);

void $Sub$$foo(void)
{
  $Super$$foo(); /* calls the original foo() function */
}

Linker Double Redirect (IAR EWARM)

1 Answers