"Ni@m" writes:

> Hi.
> Is it possible to link library to elf binary that had been already
> linked?
> For example I have test.c
>
> #include
>
> int main(int argc, char **argv)
> {
> puts("\n[^_^]\n");
>
> return 0;
> }
>
> I compile it and link it with gcc test.c -lc -o test
>
> Then I have another one, puts.c
> #include
>
> int puts(const char *s)
> {
> fputs("\n{\n", stdout);
> fputs(s, stdout);
> fputs("\n}\n", stdout);
> }
>
> Which I compile as a shared lib: gcc puts.c -shared -o puts.so -fPIC
>
> Then I want to link 'test' with puts.so to replace libc's puts. Can I
> do this?

I don't know that there's a way to relink the binary file itself, but
you can use the LD_PRELOAD environment variable to override the library
function.

$ env LD_PRELOAD=./puts.so ./test

{

[^_^]

}
$

See the man page for ld.so for more info.

> I don't know that there's a way to relink the binary file itself, but
> you can use the LD_PRELOAD environment variable to override the library
> function.
>
> $ env LD_PRELOAD=./puts.so ./test
>
Thank you for the reply.
I was thinking about LD_PRELOAD but in this case I have to keep it ENV
all the time. I don't want to use /etc/ld.so.preload because I just
want to override some functions in some tools. Well, probably wrapper
that sets LD_PRELOAD is the best solution if there is no way to
"relink".