init_priority attribute and libstdc++

init_priority attribute and libstdc++

[Václav Zeman]

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Hi.

I want to use the init_priority(prio) attribute
(https://gcc.gnu.org/onlinedocs/gcc/C_002b_002b-Attributes.html#C_002b_002b-Attributes)
to initialize stuff in my library early so that users of the library can
use the library during their own static objects construction. However,
my library uses standard C++ library facilities like std::string,
std::vector<>, etc. The question is:

What is the lowest priority for init_priority attribute that I can use
to still have libstdc++ initialize itself before my library is initialized?

-- 
VZ


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Re: init_priority attribute and libstdc++

[Václav Zeman]

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On 18.8.2014 13:25, Jonathan Wakely wrote:
> I'm on my phone so can't send plain text mail to the list, or check the
> code, but I'm pretty sure the answer is 101
> 
> Anything lower than that is reserved for the implementation so libstdc++
> would use that. Nothing in string or vector needs dynamic init anyway IIRC

Some paths of my library's initialization might try to print warnings or
errors. I have hit a SIGSEGV with the following test case, which uses
std::cerr:

~~~~
#include <iostream>

struct S1
{
    S1() { std::cerr << __FUNCTION__ << "\n"; }
} static s1 __attribute__ ((__init_priority__ (65535/2)));


int
main ()
{
  return 0;
}
~~~~

The stack trace is

~~~~
#0  0x00007ffff7b6a559 in std::ostream::sentry::sentry(std::ostream&) ()
from /usr/lib/x86_64-linux-gnu/libstdc++.so.6
#1  0x00007ffff7b6ac19 in std::basic_ostream<char,
std::char_traits<char> >& std::__ostream_insert<char,
std::char_traits<char> >(std::basic_ostream<char, std::char_traits<char>
>&, char const*, long)
    () from /usr/lib/x86_64-linux-gnu/libstdc++.so.6
#2  0x00007ffff7b6b077 in std::basic_ostream<char,
std::char_traits<char> >& std::operator<< <std::char_traits<char>
>(std::basic_ostream<char, std::char_traits<char> >&, char const*) ()
   from /usr/lib/x86_64-linux-gnu/libstdc++.so.6
#3  0x000000000040081d in S1::S1 (this=0x601172 <s1>) at test.cxx:5
#4  0x00000000004007d6 in __static_initialization_and_destruction_0
(__initialize_p=1, __priority=32767) at test.cxx:6
#5  0x00000000004007eb in _GLOBAL__sub_I.32767_main(void) () at test.cxx:13
#6  0x000000000040087d in __libc_csu_init ()
#7  0x00007ffff7731e55 in __libc_start_main (main=0x40077d <main()>,
argc=1, argv=0x7fffffffe2c8, init=0x400830 <__libc_csu_init>,
fini=<optimized out>, rtld_fini=<optimized out>,
    stack_end=0x7fffffffe2b8) at libc-start.c:246
#8  0x00000000004006b9 in _start ()
~~~~

Is this expected?

> 
> On Aug 17, 2014 8:56 PM, "Václav Zeman" <vhaisman@gmail.com
> <mailto:vhaisman@gmail.com>> wrote:
> 
>     Hi.
> 
>     I want to use the init_priority(prio) attribute
>     (https://gcc.gnu.org/onlinedocs/gcc/C_002b_002b-Attributes.html#C_002b_002b-Attributes)
>     to initialize stuff in my library early so that users of the library can
>     use the library during their own static objects construction. However,
>     my library uses standard C++ library facilities like std::string,
>     std::vector<>, etc. The question is:
> 
>     What is the lowest priority for init_priority attribute that I can use
>     to still have libstdc++ initialize itself before my library is
>     initialized?

-- 
VZ








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