From: Michael Eager <eager@eagercon.com>
To: Steve Kreyer <steve.kreyer@web.de>
Cc: gcc-help@gcc.gnu.org
Subject: Re: Symbols which were not used, still in binary
Date: Wed, 28 Jun 2006 20:17:00 -0000 [thread overview]
Message-ID: <44A2E3C9.90201@eagercon.com> (raw)
In-Reply-To: <44A2DF65.8010704@web.de>
Steve Kreyer wrote:
> Hi,
>
> I have a question about an optimization issue.
>
> I have compiled the follwing code with the command ''gcc file.c''
>
> ---------------------------------------------------------------
> int add(int a, int b){
> return a + b;
> }
>
> int main(){
> }
> --------------------------------------------------------------
>
> My question is:
> Why does the symbol "add" appear in the outcoming binary file?
> nm gives me:
> --------------------------------------------------------------
> redwing@euklid:~ $ nm a.out | grep add
> 08048324 T add
> --------------------------------------------------------------
>
> Neither is it used in this piece of code, nor is it compiled into an
> object file,
> so in my opinion it should be optimized away by gcc.
> So perhaps anybody can tell me whats wrong with my thought...
add is a global symbol. GCC has no way of knowing whether or not
this object file will be linked with another file which contains
a reference to the function. Arguably, the linker should know
that add is not referenced and could remove it, but linkers are not
usually able to slice and dice object files.
[If you declare add to be static, then GCC should be able
to eliminate it. But it doesn't.]
Programs often contain functions which are designed
to be called by someone using a debugger but are otherwise
not referenced.
--
Michael Eager eager@eagercon.com
1960 Park Blvd., Palo Alto, CA 94306 650-325-8077
next prev parent reply other threads:[~2006-06-28 20:17 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2006-06-28 19:58 Steve Kreyer
2006-06-28 20:17 ` Brian Dessent
2006-06-28 21:21 ` Steve Kreyer
2006-06-28 20:17 ` Michael Eager [this message]
2006-06-28 21:20 ` Brian Dessent
2006-06-29 5:16 ` Ingo Krabbe
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