Valgrind reports usage of uninitialised values

[Alexandre Hamez <alexandre.hamez@…>]

When running the following example with Valgrind:

#include <iostream>
#include <boost/coroutine/coroutine.hpp>

typedef boost::coroutines::coroutine<int()> generator;

void bar(generator::caller_type& yield) {
    yield(32);
}

void foo(generator::caller_type& yield) {
  generator nested_gen(bar);
  std::cout << nested_gen.get() << std::endl;
  yield(33);
}

int main() {
  generator gen(foo);
  std::cout << gen.get() << std::endl;
  return 0;
};

I get the following trace (this is an extract, I give only the first error):

$ valgrind --max-stackframe=6516920  --track-origins=yes ./a.out

==10734== Memcheck, a memory error detector
==10734== Copyright (C) 2002-2012, and GNU GPL'd, by Julian Seward et al.
==10734== Using Valgrind-3.8.1 and LibVEX; rerun with -h for copyright info
==10734== Command: ./a.out
==10734==
==10734== Warning: client switching stacks?  SP change: 0x7ff0001b8 --> 0x512af98
==10734==          to suppress, use: --max-stackframe=34257850912 or greater
==10734== Warning: client switching stacks?  SP change: 0x512aca8 --> 0x5761f98
==10734==          to suppress, use: --max-stackframe=6517488 or greater
==10734== Use of uninitialised value of size 8
==10734==    at 0x4C0E727: jump_fcontext (in /home/ahamez/usr/boost1.54/lib/libboost_context.so.1.54.0)
==10734==    by 0x40C6E9: boost::coroutines::detail::coroutine_object<int (), void (*)(boost::coroutines::coroutine<void (int), 1>&), boost::coroutines::detail::standard_stack_allocator, std::allocator<boost::coroutines::coroutine<int (), 0> >, boost::coroutines::coroutine<void (int), 1>, int, 0>::coroutine_object(void (*)(boost::coroutines::coroutine<void (int), 1>&), boost::coroutines::attributes const&, boost::coroutines::detail::standard_stack_allocator const&, std::allocator<boost::coroutines::detail::coroutine_object<int (), void (*)(boost::coroutines::coroutine<void (int), 1>&), boost::coroutines::detail::standard_stack_allocator, std::allocator<boost::coroutines::coroutine<int (), 0> >, boost::coroutines::coroutine<void (int), 1>, int, 0> > const&) (in /home/ahamez/a.out)
==10734==    by 0x407F29: boost::coroutines::coroutine<int (), 0>::coroutine<void (*)(boost::coroutines::coroutine<void (int), 1>&)>(void (*)(boost::coroutines::coroutine<void (int), 1>&), boost::coroutines::attributes const&, boost::coroutines::detail::standard_stack_allocator const&, std::allocator<boost::coroutines::coroutine<int (), 0> > const&, boost::disable_if<boost::is_convertible<void (*&)(boost::coroutines::coroutine<void (int), 1>&), boost::rv<void (*)(boost::coroutines::coroutine<void (int), 1>&)>&>, boost::coroutines::coroutine<int (), 0>::dummy*>::type) (in /home/ahamez/a.out)
==10734==    by 0x403DB9: foo(boost::coroutines::coroutine<void (int), 1>&) (in /home/ahamez/a.out)
==10734==    by 0x410A1C: boost::coroutines::detail::coroutine_object<int (), void (*)(boost::coroutines::coroutine<void (int), 1>&), boost::coroutines::detail::standard_stack_allocator, std::allocator<boost::coroutines::coroutine<int (), 0> >, boost::coroutines::coroutine<void (int), 1>, int, 0>::run() (in /home/ahamez/a.out)
==10734==    by 0x40EAC6: void boost::coroutines::detail::trampoline1<boost::coroutines::detail::coroutine_object<int (), void (*)(boost::coroutines::coroutine<void (int), 1>&), boost::coroutines::detail::standard_stack_allocator, std::allocator<boost::coroutines::coroutine<int (), 0> >, boost::coroutines::coroutine<void (int), 1>, int, 0> >(long) (in /home/ahamez/a.out)
==10734==    by 0x4C0E6BD: make_fcontext (in /home/ahamez/usr/boost1.54/lib/libboost_context.so.1.54.0)
==10734==  Uninitialised value was created by a stack allocation
==10734==    at 0x4C0E723: jump_fcontext (in /home/ahamez/usr/boost1.54/lib/libboost_context.so.1.54.0)

Tested under MacOS X 10.8 with clang 3.3 and under Linux (CentOS 6) with gcc 4.8. I can't say if it's just Valgrind which can't cope with coroutines or if it's a real bug from Boost.Coroutine.

[olli]

coroutines swap the stack-pointer (and some other registers) which might confuse valgrind. 'Warning: client switching stacks? SP change: 0x512aca8 -->'