Question

all.

I want to link a library which calls malloc() function.
However, my target environment is different one and
malloc() is supplied as inline-function.

How can I make the library’s call to malloc() direct to
my target environment’s malloc() routine?

Is it any way to change the exported function name? If so
I can code my_malloc() first and export it as malloc() and link
the library to that one:

#include <my_environment.h>  // malloc() is inline function declared there 
void my_malloc (void) {
   malloc (void);             
}

---

More specifically,
the library is one from linux distro so it depends on libc.
But my environment is embedded one and has no libc library and malloc(), free(), … are custom-implemented. Some are inline functions and some are library functions.

Answer 1

The GNU linker (ld) supports a --wrap=functionname parameter. I’ll simply quote the documentation from the man page as it includes an example which should do exactly what you need:

–wrap=symbol Use a wrapper function for symbol. Any undefined reference to symbol will be resolved to “__wrap_symbol”. Any undefined reference to “__real_symbol” will be resolved to symbol.

This can be used to provide a wrapper for a system function. The wrapper function should be called “__wrap_symbol”. If it wishes to call the system function, it should call “__real_symbol”.

Here is a trivial example:

void *
__wrap_malloc (size_t c)
{
    printf ("malloc called with %zu\n", c);
    return __real_malloc (c);
}

If you link other code with this file using --wrap malloc, then all calls to “malloc” will call the function "__wrap_malloc” instead. The call to “__real_malloc” in “__wrap_malloc” will call the real “malloc” function.

You may wish to provide a “__real_malloc” function as well, so that links without the --wrap option will succeed. If you do this, you should not put the definition of “__real_malloc” in the same file as “__wrap_malloc“; if you do, the assembler may resolve the call before the linker has a chance to wrap it to “malloc“.