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Re: Constructor of external lib called too early

On 29 July 2013 19:14, Florian Weimer <> wrote:
> On 07/29/2013 03:16 PM, Siddhesh Poyarekar wrote:
>> The constructors are usually called like this from the linker:
>>    if (l->l_info[DT_INIT] != NULL)
>>      {
>>        init_t init = (init_t) DL_DT_INIT_ADDRESS
>>          (l, l->l_addr + l->l_info[DT_INIT]->d_un.d_ptr);
>>        /* Call the function.  */
>>        init (argc, argv, env);
>>      }
>> So if your constructor accepts argc, argv and envp, you might be able
>> to get the environment from its argument.  This is a NULL terminated
>> array, so you will have to do your own traversal and matching.  I
>> don't know if this is documented anywhere, so I don't know if it is
>> the canonical way to do this.
>> You also have to make sure you don't traverse the environment if the
>> executed binary is suid.
> Will getauxval(AT_SECURE) work at this point?  Is there some other way to
> access the auxiliary vector (besides parsing /proc)?

getauxval won't work since its internal structures are only
initialized a little before calling program main.  You could traverse
to the end of envp and access the auxv drectly though.


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