GDB可以调试C ++ lambdas吗？

Question

I use C++ 11 features actively. I have program created in Visual Studio 2013 that relies on lambdas to run multiple threads (lambda represents task, and thread receives lambda instance that it has to run). Lambda is defined in static library and linked in executable file that calls it from thread created by this executable file. When I try to debug Linux version of this application with GDB, it looks like GDB can not step into method that contains lambda. It can not set breakpoints in this function, and when I try to step into, it even steps in methods that lambda calls from its body, but after return from these methods it doesn't go to lambda body, it goes to next method that lambda calls, etc. Are there any way to debug lambdas body with GDB?

Answer 1

I've seen them in stack traces before, so it does at least know about them. I've never tried setting a normal breakpoint in one. It's sort of a hack, but you can set a breakpoint in one (or anywhere) by using asm volatile("int $3"); on x86(-64).

Here's an example program:

int main(){
    auto f = [](){
        asm volatile("int $3");
    };
    f();
    return 0;
}

Here's it's backtrace when it hits that breakpoint:

#0  0x0000000000400577 in main::{lambda()#1}::operator()() const ()
#1  0x000000000040058d in main ()

Answer 2

From my experience, gdb cannot step into lambdas -- it just skips over them. Not only that, stepping into a lambda definition seems to confuse gdb and it proceeds to the end of the current function. You can, however, place a breakpoint explicitly inside a lambda, and if you hit that point, you will stop. This is obviously far from ideal.

Answer 3

Step into Lamba's .run() go next/step (jump initializations) until the following call:

std::forward<>(args)(...)

Step into this one. It will lead you to you lambda body code.