How to get LD_DEBUG of forked process

[Ajeet Yadav]

On Thu, Oct 11, 2012 at 10:33 PM, David Daney <ddaney.cavm@gmail.com> wrote:
> On 10/10/2012 11:30 PM, Ajeet Yadav wrote:
>>
>> Dear All,
>> I wish to check the the LD_DEBUG=reloc for both parent and child process.
>>
>> Code of parent process p1, that is forking the child process p2
>> [ajeet_y@localhost ajeet]$ cat main1.c
>> #include <stdio.h>
>> #include <unistd.h>
>> int main()
>> {
>>          pid_t pid;
>>          printf("In P1\n");
>>          pid = fork();
>>          if (pid){
>>                  sleep(1);
>>          } else {
>>                  execve("./p2",NULL,NULL);
>
>
> Here you completely replace the Environment of the process execing p2.
>
>>          }
>> }
>
> [...]
>
>
>>
>>
>> Can anyone help me why I am not getting the relocation information of
>> process P2,
>
>
> You are not getting the LD_DEBUG=reloc information because that environment
> variable is not set in P2 due to your elimination of the entire environment.
>
>
>>  and how to get it ?
>
>
> Pass LD_DEBUG=reloc in the environment of any process for which you wish to
> see the dumps.
>
Thanks, I did the same with system("p2") in this case I get the
LD_DEBUG=reloc information for both, knowing that system() works, I
checked its fork:exec implementation. As you suggested, I did
execve("./p2", NULL, __environ), in this case also I did not get p2
information, finally I did

char *argv={"./p2",NULL};
execve("./p2", argv, __environ); now this works perfect.

3 arg is mandatory, but I did not understand, Why I need to pass 2nd arg ?