Re: looking for a way to tell gcc not to remove some code he thinks is unreachable.
On 03/07/2011 12:11 PM, Erez D wrote: > I have a function which is not called in a regular way, so gcc thinks > it is dead code. > however it is not, and i am looking for a way to tell the linker not > to remove it. > > i can call it from some place with a flag that tells it to do nothing, > but this is a ugly hack > is there a directive telling gcc not to remove that certain function ? > I did not exactly try, but if there is -fdce, which is by default enabled an -O*, there should be also -fno-dce and fno-tree-dce, is it not? > thanks, > erez. > > > ___ > Linux-il mailing list > Linux-il@cs.huji.ac.il > http://mailman.cs.huji.ac.il/mailman/listinfo/linux-il ___ Linux-il mailing list Linux-il@cs.huji.ac.il http://mailman.cs.huji.ac.il/mailman/listinfo/linux-il
Re: looking for a way to tell gcc not to remove some code he thinks is unreachable.
On Mon, Mar 7, 2011 at 3:30 PM, Elazar Leibovich wrote: > 2011/3/7 Orna Agmon Ben-Yehuda > > >> >> On Mon, Mar 7, 2011 at 12:18 PM, Muli Ben-Yehuda wrote: >> >>> On Mon, Mar 07, 2011 at 12:11:36PM +0200, Erez D wrote: >>> >>> > I have a function which is not called in a regular way, so gcc >>> > thinks it is dead code. however it is not, and i am looking for a >>> > way to tell the linker not to remove it. >>> >>> extern >>> >>> >>> And set the function pointer to a global variable, so that the linker >> cannot know if the value is used or not. >> This trick I learned from Nadav Har'El worked through many compilers and >> linkers over the past decade. >> > > I wonder if link time optimization[1] would be able to catch this trick and > remove the dead code after all. > > The smarter the compiler become, the smarter we should trick them into > unexpected behavior > > [1] http://gcc.gnu.org/wiki/LinkTimeOptimization > Worst case, you can always print this value. Anyway, I prefer this trick, which is performed in code to the KEEP trick which requires changing the linker itself, because it is more portable. -- Orna Agmon Ben-Yehuda. http://ladypine.org ___ Linux-il mailing list Linux-il@cs.huji.ac.il http://mailman.cs.huji.ac.il/mailman/listinfo/linux-il
Re: looking for a way to tell gcc not to remove some code he thinks is unreachable.
2011/3/7 Orna Agmon Ben-Yehuda > > > On Mon, Mar 7, 2011 at 12:18 PM, Muli Ben-Yehuda wrote: > >> On Mon, Mar 07, 2011 at 12:11:36PM +0200, Erez D wrote: >> >> > I have a function which is not called in a regular way, so gcc >> > thinks it is dead code. however it is not, and i am looking for a >> > way to tell the linker not to remove it. >> >> extern >> >> >> And set the function pointer to a global variable, so that the linker > cannot know if the value is used or not. > This trick I learned from Nadav Har'El worked through many compilers and > linkers over the past decade. > I wonder if link time optimization[1] would be able to catch this trick and remove the dead code after all. The smarter the compiler become, the smarter we should trick them into unexpected behavior [1] http://gcc.gnu.org/wiki/LinkTimeOptimization ___ Linux-il mailing list Linux-il@cs.huji.ac.il http://mailman.cs.huji.ac.il/mailman/listinfo/linux-il
Re: looking for a way to tell gcc not to remove some code he thinks is unreachable (SOVED)
As I was already manipulating the linker script, i added a KEEP(). now it
does not remove the funnction, or anything that is being addressed by it.
cheers,
erez.
On Mon, Mar 7, 2011 at 2:06 PM, Erez D wrote:
>
>
> On Mon, Mar 7, 2011 at 1:33 PM, Muli Ben-Yehuda wrote:
>
>> On Mon, Mar 07, 2011 at 12:27:08PM +0200, Erez D wrote:
>>
>> > int x;
>> >
>> > void a()
>>
>> extern void a()
>>
> doesn't work
> avr32-gcc 4.3.2
>
>>
>> > {
>> > x=3;
>> > }
>> >
>> > int main()
>> > {
>> > x=0;
>> > return 1;
>> > }
>> >
>> >
>> >
>> > the linker will remove function a() as it is not called from
>> > enywhere. however, i need it to be there, including all of its
>> > content.
>>
>> gcc (ld) 4.4.3 does not remove it in this case. What linker are you
>> using?
>>
>> Cheers,
>> Muli
>>
>
>
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Re: looking for a way to tell gcc not to remove some code he thinks is unreachable.
On Mon, Mar 7, 2011 at 1:33 PM, Muli Ben-Yehuda wrote:
> On Mon, Mar 07, 2011 at 12:27:08PM +0200, Erez D wrote:
>
> > int x;
> >
> > void a()
>
> extern void a()
>
doesn't work
avr32-gcc 4.3.2
>
> > {
> > x=3;
> > }
> >
> > int main()
> > {
> > x=0;
> > return 1;
> > }
> >
> >
> >
> > the linker will remove function a() as it is not called from
> > enywhere. however, i need it to be there, including all of its
> > content.
>
> gcc (ld) 4.4.3 does not remove it in this case. What linker are you
> using?
>
> Cheers,
> Muli
>
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Re: looking for a way to tell gcc not to remove some code he thinks is unreachable.
On Mon, Mar 7, 2011 at 1:49 PM, Orna Agmon Ben-Yehuda wrote: > > > On Mon, Mar 7, 2011 at 12:18 PM, Muli Ben-Yehuda wrote: > >> On Mon, Mar 07, 2011 at 12:11:36PM +0200, Erez D wrote: >> >> > I have a function which is not called in a regular way, so gcc >> > thinks it is dead code. however it is not, and i am looking for a >> > way to tell the linker not to remove it. >> >> extern >> >> >> And set the function pointer to a global variable, so that the linker > cannot know if the value is used or not. > This trick I learned from Nadav Har'El worked through many compilers and > linkers over the past decade. > i know this hack, but i preffered a direct method thanks, erez. > > >> ___ >> Linux-il mailing list >> Linux-il@cs.huji.ac.il >> http://mailman.cs.huji.ac.il/mailman/listinfo/linux-il >> > > > > -- > Orna Agmon Ben-Yehuda. > http://ladypine.org > ___ Linux-il mailing list Linux-il@cs.huji.ac.il http://mailman.cs.huji.ac.il/mailman/listinfo/linux-il
Re: looking for a way to tell gcc not to remove some code he thinks is unreachable.
On Mon, Mar 7, 2011 at 12:18 PM, Muli Ben-Yehuda wrote: > On Mon, Mar 07, 2011 at 12:11:36PM +0200, Erez D wrote: > > > I have a function which is not called in a regular way, so gcc > > thinks it is dead code. however it is not, and i am looking for a > > way to tell the linker not to remove it. > > extern > > > And set the function pointer to a global variable, so that the linker cannot know if the value is used or not. This trick I learned from Nadav Har'El worked through many compilers and linkers over the past decade. > ___ > Linux-il mailing list > Linux-il@cs.huji.ac.il > http://mailman.cs.huji.ac.il/mailman/listinfo/linux-il > -- Orna Agmon Ben-Yehuda. http://ladypine.org ___ Linux-il mailing list Linux-il@cs.huji.ac.il http://mailman.cs.huji.ac.il/mailman/listinfo/linux-il
Re: looking for a way to tell gcc not to remove some code he thinks is unreachable.
On Mon, Mar 07, 2011 at 12:27:08PM +0200, Erez D wrote:
> int x;
>
> void a()
extern void a()
> {
> x=3;
> }
>
> int main()
> {
> x=0;
> return 1;
> }
>
>
>
> the linker will remove function a() as it is not called from
> enywhere. however, i need it to be there, including all of its
> content.
gcc (ld) 4.4.3 does not remove it in this case. What linker are you
using?
Cheers,
Muli
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Re: looking for a way to tell gcc not to remove some code he thinks is unreachable.
On Mon, Mar 7, 2011 at 12:34 PM, Raz wrote:
> why do you think the linker removes the function ? what flags are using ?
> Please nm ( nm ).
>
objdump -d does not show assembly for function a
>
> 2011/3/7 Erez D
>
>>
>>
>> On Mon, Mar 7, 2011 at 12:18 PM, Muli Ben-Yehuda wrote:
>>
>>> On Mon, Mar 07, 2011 at 12:11:36PM +0200, Erez D wrote:
>>>
>>> > I have a function which is not called in a regular way, so gcc
>>> > thinks it is dead code. however it is not, and i am looking for a
>>> > way to tell the linker not to remove it.
>>>
>>> extern
>>>
>>> how ?
>> sorry, didn't get what you mean.
>>
>> i'll give an example:
>>
>> === my code
>> int x;
>>
>> void a()
>> {
>> x=3;
>> }
>>
>> int main()
>> {
>> x=0;
>> return 1;
>> }
>>
>>
>>
>> the linker will remove function a() as it is not called from enywhere.
>> however, i need it to be there, including all of its content.
>>
>> how do i do that.
>>
>>
>> ___
>> Linux-il mailing list
>> Linux-il@cs.huji.ac.il
>> http://mailman.cs.huji.ac.il/mailman/listinfo/linux-il
>>
>>
>
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Re: looking for a way to tell gcc not to remove some code he thinks is unreachable.
why do you think the linker removes the function ? what flags are using ?
Please nm ( nm ).
2011/3/7 Erez D
>
>
> On Mon, Mar 7, 2011 at 12:18 PM, Muli Ben-Yehuda wrote:
>
>> On Mon, Mar 07, 2011 at 12:11:36PM +0200, Erez D wrote:
>>
>> > I have a function which is not called in a regular way, so gcc
>> > thinks it is dead code. however it is not, and i am looking for a
>> > way to tell the linker not to remove it.
>>
>> extern
>>
>> how ?
> sorry, didn't get what you mean.
>
> i'll give an example:
>
> === my code
> int x;
>
> void a()
> {
> x=3;
> }
>
> int main()
> {
> x=0;
> return 1;
> }
>
>
>
> the linker will remove function a() as it is not called from enywhere.
> however, i need it to be there, including all of its content.
>
> how do i do that.
>
>
> ___
> Linux-il mailing list
> Linux-il@cs.huji.ac.il
> http://mailman.cs.huji.ac.il/mailman/listinfo/linux-il
>
>
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Re: looking for a way to tell gcc not to remove some code he thinks is unreachable.
On Mon, Mar 7, 2011 at 12:18 PM, Muli Ben-Yehuda wrote:
> On Mon, Mar 07, 2011 at 12:11:36PM +0200, Erez D wrote:
>
> > I have a function which is not called in a regular way, so gcc
> > thinks it is dead code. however it is not, and i am looking for a
> > way to tell the linker not to remove it.
>
> extern
>
> how ?
sorry, didn't get what you mean.
i'll give an example:
=== my code
int x;
void a()
{
x=3;
}
int main()
{
x=0;
return 1;
}
the linker will remove function a() as it is not called from enywhere.
however, i need it to be there, including all of its content.
how do i do that.
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Re: looking for a way to tell gcc not to remove some code he thinks is unreachable.
On Mon, Mar 07, 2011 at 12:11:36PM +0200, Erez D wrote: > I have a function which is not called in a regular way, so gcc > thinks it is dead code. however it is not, and i am looking for a > way to tell the linker not to remove it. extern ___ Linux-il mailing list Linux-il@cs.huji.ac.il http://mailman.cs.huji.ac.il/mailman/listinfo/linux-il
looking for a way to tell gcc not to remove some code he thinks is unreachable.
I have a function which is not called in a regular way, so gcc thinks it is dead code. however it is not, and i am looking for a way to tell the linker not to remove it. i can call it from some place with a flag that tells it to do nothing, but this is a ugly hack is there a directive telling gcc not to remove that certain function ? thanks, erez. ___ Linux-il mailing list Linux-il@cs.huji.ac.il http://mailman.cs.huji.ac.il/mailman/listinfo/linux-il
