[Buildroot] [autobuild.buildroot.net] Daily results for 2020-09-10

[Yann E. MORIN <yann.morin.1998@free.fr>]

Micheal, All,

On 2020-09-11 23:12 +0200, Michael Nosthoff spake thusly:
> >>>>>On 11.09.2020 09:08, Thomas Petazzoni wrote:
> >>>>>>   mips64el   |        host-grpc-1.31.0        | NOK | http://autobuild.buildroot.net/results/b554f6f2fb66892273f7520ad6e36923557b229e |
[--SNIP--]
> I did some further testing using a fresh docker container `ubuntu:trusty`.
> I derived a simple test which mirrors the failing code in [1].
> If you compile this code using `g++ --std=c++11 main.cpp -lpthread -o
> thread_test`
> 
> ```
> #include <thread>
> #include <cassert>
> 
> main() {
> ? ??? std::thread::id runner;
> ??? auto me = std::this_thread::get_id();
> 
> ??? assert(runner != me);
> }
> ```
> 
> running the resulting program will throw the assert. Doing the identical
> thing in a `debian:jessie` container with g++-4.8 will finish successfully.
> 
> What's happening in this code? When pthreads is not linked glibc's
> implementation of std::thread::id is used.
> But this has a bug that it can't differentiate between a default initialized
> id and the result of the get_id() call when you have no threading.
> This is addressed in [0] which lead to a fix in gcc-6.
> 
> But we are linking with -lpthread. So this bug should not affect us. So when
> I try to actually create a thread like
> 
> ```
> std::thread worker([](){});
> ```
> 
> I get a crash when running the program. Which proves that pthread is not
> actually linkend. Doing the same on debian yields a working program.
> Even when I compile the program on debian and copy it to ubuntu the program
> runs successfully. So it is not a runtime thing.
> 
> When I change the compiler flag to -pthread I suddenly get a working program
> on ubuntu.

Whoa! Great investigation! ?

> This brings me to two possible solutions:
> 
> - find out why in ubuntu:trusty -lpthread is not working

Is it a bug in gcc-4.8 that is not fixed in Ubuntu but is in Debian? Or
is it a patch that Ubuntu applies that Debian does not?

> - ensure that protobuf uses -pthread instead of -lpthread (i have to check
> what is cmake decides to use on other compilers).
> 
> I'll check this next week.

Thanks! This is really very much appreciated! :-)

Regards,
Yann E. MORIN.

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