Regression on prelinked-sepdebug-shlibs
Tristan Gingold
gingold@adacore.com
Thu Jan 7 11:02:00 GMT 2010
On Jan 6, 2010, at 8:16 PM, Daniel Jacobowitz wrote:
> On Wed, Jan 06, 2010 at 07:05:10PM +0100, Jan Kratochvil wrote:
>> On Wed, 06 Jan 2010 17:38:55 +0100, Tristan Gingold wrote:
>>> I think this is not correct: the separate debug file may have one section at
>>> zero while the main may not. In the above code, we do not consider wether
>>> an offset is used.
>>>
>>> I am not sure that this can happen with ELF however.
>
> Sorry, I don't quite understand this.
I am not sure that you can create a linux native executable with a section whose vma is 0.
I tried this:
$ cat sep.c
#include <stdio.h>
int zero (void) __attribute__((section("sec_zero")));
int zero (void)
{
return 0;
}
int main (void)
{
printf ("Zero=%d\n", zero ());
return 0;
}
$ gcc -c -g sep.c
$ gcc -o sep sep.o -Wl,--section-start,sec_zero=0
But unfortunately linux refuses to execute that (I got a sigkill very very early) so I can't play with that.
(and I haven't investigated further in the kernel ;-)
>> This has_section_at_zero feature is intended for embedded targets. I only
>> know has_section_at_zero can never happen for cases I am aware of.
>>
>> IMHO embedded targets do not use the file-vs-memory offsets but not sure.
>> Also the embedded targets probably do not use .linkonce/COMDAT - this is why
>> this has_section_at_zero differentiator could work.
>
> An embedded program can use either of these things. The
> linkonce/comdat issue is a constant problem, but this was the best
> available heuristic.
I agree that this heuristic make sense. However I don't think that the one used for separate debug objfile
is correct. I will submit a patch to discuss this point.
Tristan.
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