RE: Optimization - removing unused code

RE: Optimization - removing unused code

[Madani, Srikanth, VF-DE]

Following up the thread titled "RE: ld warning (was Optimization, remove unused code from  Image)":

> Will retry on a Linux machine where everything is GNU, and see if I have
> better results there.

#Compilation : gcc version 3.3.1 (SuSE Linux)
$> gcc -c -ffunction-sections *.c

#Linking : GNU ld version 2.14.90.0.5 20030722 (SuSE Linux)
$> gcc -Wl,--gc-sections *.o

$> file a.out
a.out: ELF 32-bit LSB executable, Intel 80386, version 1 (SYSV), for GNU/Linux 2.2.5, dynamically linked (uses shared libs), not stripped

a.out works fine, but contains the uncalled function func3() in the code section.

If I link it statically, however:
$> gcc -Wl,--gc-sections,-static *.o

$> file a.out
a.out: ELF 32-bit LSB executable, Intel 80386, version 1 (SYSV), statically linked, not stripped


And a.out doesn't contain func3(). AND, it doesn't contain func2() either.

So, unused code has been removed - but only (as man ld stipulates) if you link statically.

Cheers,  
Srikanth Madani
Düsseldorf, NRW




________________________________________________________________
The source files are:
 
$> cat hello.c
int main(void) {
        printf("\nHello world!\n");
        func1();
        exit(0);
}
$>


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


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

RE: Optimization - removing unused code

[Ramana Radhakrishnan]

Hi,


Yeah I can imagine why it would be hard to do --gc-sections for
dynamically linked executables . You would have to worry about the
semantics of weak  symbol definitions , weak function definitions to worry
about. Other than that I can't think of any other issues off the cuff. It
looks as though no one has done it yet and possibly would be a nifty
feature to have,  though using google I could only find this thread as a
reference :

http://sources.redhat.com/ml/binutils/2001-11/msg00339.html

and more specifically this reply :

http://sources.redhat.com/ml/binutils/2001-11/msg00350.html


In any case maybe future discussions about this should possibly move to
binutils@sources.redhat.com and maybe no longer here.

cheers
Ramana

---
Ramana Radhakrishnan
GNU Tools Support
codito ergo sum (www.codito.com)



> Following up the thread titled "RE: ld warning (was Optimization, remove
> unused code from  Image)":
>
>> Will retry on a Linux machine where everything is GNU, and see if I have
>> better results there.
>
> #Compilation : gcc version 3.3.1 (SuSE Linux)
> $> gcc -c -ffunction-sections *.c
>
> #Linking : GNU ld version 2.14.90.0.5 20030722 (SuSE Linux)
> $> gcc -Wl,--gc-sections *.o
>
> $> file a.out
> a.out: ELF 32-bit LSB executable, Intel 80386, version 1 (SYSV), for
> GNU/Linux 2.2.5, dynamically linked (uses shared libs), not stripped
>
> a.out works fine, but contains the uncalled function func3() in the code
> section.
>
> If I link it statically, however:
> $> gcc -Wl,--gc-sections,-static *.o
>
> $> file a.out
> a.out: ELF 32-bit LSB executable, Intel 80386, version 1 (SYSV),
> statically linked, not stripped
>
>
> And a.out doesn't contain func3(). AND, it doesn't contain func2() either.
>
> So, unused code has been removed - but only (as man ld stipulates) if you
> link statically.
>
> Cheers,
> Srikanth Madani
> Düsseldorf, NRW
>
>
>
>
> ________________________________________________________________
> The source files are:
>
> $> cat hello.c
> int main(void) {
>         printf("\nHello world!\n");
>         func1();
>         exit(0);
> }
> $>
>
>
> $> cat fun1.c
> void func1(void) {
>         printf("\nIn function func1()\n");
> }
> void func2(void) {
>         func3();
> }
> $>
>
>
> $> cat fun2.c
> void func3(void) {
>         printf("\nIn function func3()\n");
> }
> $>
>


----
Ramana Radhakrishnan
Codito Technologies