[OT] Prevent linker from unnecessary symbol resolution

[OT] Prevent linker from unnecessary symbol resolution

[Srikanth Madani]

Hi,

Suppose I have a C file fun1.c containing two functions:

__________
void func1() {
        printf("\nIn function func1()\n");
}
void func2() {
        func3();
}
___________

and another called hello.c containing:

___________
void main() {
          func1();
}
___________

Is it possible to create a staticly linked binary using just these two
source files? Or do I have to provide a function definition for func3(),
even though it is not called.

Cheers,
Srikanth Madani

Re: [OT] Prevent linker from unnecessary symbol resolution

[Ian Lance Taylor]

Srikanth Madani <srikanth.madani@vodafone.com> writes:

> Suppose I have a C file fun1.c containing two functions:
> 
> __________
> void func1() {
>         printf("\nIn function func1()\n");
> }
> void func2() {
>         func3();
> }
> ___________
> 
> and another called hello.c containing:
> 
> ___________
> void main() {
>           func1();
> }
> ___________
> 
> Is it possible to create a staticly linked binary using just these two
> source files? Or do I have to provide a function definition for func3(),
> even though it is not called.

You have to define func3.  You could do it on the linker command line
using something along the lines of '-Wl,--defsym,func3=0'.

If you compile with -ffunction-sections and link with --gc-sections,
you might get away with not defining func3.  I haven't tried it,
though, and it would be inherently system dependent.

Ian

RE: [OT] Prevent linker from unnecessary symbol resolution

[Srikanth Madani]

Thanks for the response Ian.

So, the conclusion is that my binary is stuck with unnecessary relocatable
code (of a function func3() which main() doesn't call).
Of course, I don't call func2() either, but I can accept that - as it is
defined within an object file which I use (fun1.o)

My interest in all this is to remove unused functions, and thus reduce the
size of my final binary.

I did find another thread on this list which dealt with removing dead code.
Here's the Google cache :
http://66.102.11.104/search?q=cache:5y73E-67cZAJ:gcc.gnu.org/ml/gcc-help/200
3-08/msg00128.html++site:gcc.gnu.org+removing+dead+code&hl=en

I'm not sure I can do this under Solaris though - I will post an update if I
manage it.

Best regards,
Srikanth Madani

ps: Here's the entire scenario - if someone wishes to recreate it.

[181]> \ls *.c
fun1.c    fun2.c    hello.c

[182]> cat fun1.c
void func1() {
        printf("\nIn function func1()\n");
}
void func2() {
        func3();
}


[183]> cat fun2.c
void func3() {
        printf("\nIn function func3()\n");
}


[184]> cat hello.c
void main() {
        func1();
}

[185]> cc hello.c fun1.c
hello.c:
fun1.c:
Undefined                       first referenced
 symbol                             in file
func3                               fun1.o
ld: fatal: Symbol referencing errors. No output written to a.out


And if I use fun2.c as well - then all goes well.

[186]> cc hello.c fun1.c fun2.c
hello.c:
fun1.c:
fun2.c:

[187]> \ls a.out
a.out