In C, is it possible to change exported function name to different one?

Question

all.

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

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".

Answer 2

What about:

#define malloc my_malloc
#include <my_environment.h>
#undef malloc

int malloc(size_t sz)
{
   return my_malloc(sz);
}

#define malloc my_malloc
// use your malloc here

Answer 3

I think the alias attribute might solve your problem:

alias ("target")
    The alias attribute causes the declaration to be emitted as an alias for another symbol, which must be specified. For instance,

              void __f () { /* Do something. */; }
              void f () __attribute__ ((weak, alias ("__f")));


    defines `f' to be a weak alias for `__f'. In C++, the mangled name for the target must be used. It is an error if `__f' is not defined in the same translation unit.

    Not all target machines support this attribute.

http://gcc.gnu.org/onlinedocs/gcc/Function-Attributes.html