[ECOS] What happens during optimization

[ECOS] What happens during optimization

[Daniel Lidsten]

Hi,

I have run my system on a debug version of eCos but now i want to try some optimization. I removed all debug info (-gdwarf) and added the flag -O2.

When i link my application to the new eCos then i get some "undefined reference" regarding some thread functions like Cyg_Thread::self.

The above function are probably removed due to the optimization and i was wondering if there are any way of forcing it to be a part of the final library?

Regards, Daniel

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Re: [ECOS] What happens during optimization

[Gary Thomas]

On Fri, 2002-11-15 at 07:47, Daniel Lidsten wrote:
> Hi,
> 
> I have run my system on a debug version of eCos but now i want to try some optimization. I removed all debug info (-gdwarf) and added the flag -O2.
> 
> When i link my application to the new eCos then i get some "undefined reference" regarding some thread functions like Cyg_Thread::self.
> 
> The above function are probably removed due to the optimization and i was wondering if there are any way of forcing it to be a part of the final library?

Did you rebuild everything after you added the optimization option?

Note: optimization and debugging info (-gdwarf) can both be present
although debugging may be more difficult.

Note2: our default builds always use optimization.

-- 
------------------------------------------------------------
Gary Thomas                  |
eCosCentric, Ltd.            |  
+1 (970) 229-1963            |  eCos & RedBoot experts
gthomas@ecoscentric.com      |
http://www.ecoscentric.com/  |
------------------------------------------------------------


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Re: [ECOS] What happens during optimization

[Grant Edwards]

On Fri, Nov 15, 2002 at 07:53:20AM -0700, Gary Thomas wrote:

> Did you rebuild everything after you added the optimization option?

Is it required that eCos and the app be compiled with the same
level of optimization?

-- 
Grant Edwards
grante@visi.com

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Re: [ECOS] What happens during optimization

[Gary Thomas]

On Fri, 2002-11-15 at 08:40, Grant Edwards wrote:
> On Fri, Nov 15, 2002 at 07:53:20AM -0700, Gary Thomas wrote:
> 
> > Did you rebuild everything after you added the optimization option?
> 
> Is it required that eCos and the app be compiled with the same
> level of optimization?

It all depends, but in general I would go for that.

The quoted example was apt;  the guy built his program and the
eCos kernel with no optimization.  Thus Cyg_Thread::self was a
real function.  When he rebuilt the kernel with optimization,
all of the uses of Cyg_Thread::self were inlined, thus there
was no copy for his code to link against.

Mixed optimized/not-optimized code can run into these sort
of problems where inline functions simply disappear.

-- 
------------------------------------------------------------
Gary Thomas                  |
eCosCentric, Ltd.            |  
+1 (970) 229-1963            |  eCos & RedBoot experts
gthomas@ecoscentric.com      |
http://www.ecoscentric.com/  |
------------------------------------------------------------


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Re: [ECOS] What happens during optimization

[Scott Dattalo]

On 15 Nov 2002, Gary Thomas wrote:

> On Fri, 2002-11-15 at 08:40, Grant Edwards wrote:
> > On Fri, Nov 15, 2002 at 07:53:20AM -0700, Gary Thomas wrote:
> > 
> > > Did you rebuild everything after you added the optimization option?
> > 
> > Is it required that eCos and the app be compiled with the same
> > level of optimization?
> 

I was going to ask a very similar question.

> It all depends, but in general I would go for that.

> 
> The quoted example was apt;  the guy built his program and the
> eCos kernel with no optimization.  Thus Cyg_Thread::self was a
> real function.  When he rebuilt the kernel with optimization,
> all of the uses of Cyg_Thread::self were inlined, thus there
> was no copy for his code to link against.
> 
> Mixed optimized/not-optimized code can run into these sort
> of problems where inline functions simply disappear.


In my case, I compiled my app with -O3. I didn't explicitly change the 
eCos opitimization (so it's presumably the default). My code linked just 
fine but didn't run properly. I did not investigate this in detail, but I 
suspect it's due to some inline assembly code (that I wrote).

Scott


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