rust - 如何在异步函数中设置断点？

Question

我有一个要调试的async方法的结构。我用gdb设置了一个调试版本的断点。这是停在async方法Strct::async_method上的代码的样子:

0x5555557f4a6a <bin::Strct::async_method+26>            mov    QWORD PTR [rsp+0x10],rsi
0x5555557f4a6f <bin::Strct::async_method+31>            mov    QWORD PTR [rsp+0x18],rdx
0x5555557f4a74 <bin::Strct::async_method+36>            mov    BYTE PTR [rsp+0x112],0x0
0x5555557f4a7c <bin::Strct::async_method+44>            lea    rsi,[rsp+0x10]
0x5555557f4a81 <bin::Strct::async_method+49>            mov    QWORD PTR [rsp+0x8],rax
0x5555557f4a86 <bin::Strct::async_method+54>            call   0x5555557e6970 <core::future::from_generator>

该代码调用 core::future::from_generator，这不是我想要调试的。暂停 async方法主体执行的正确方法是什么？

Answer 1

让我们用它作为我们的MRE

use futures::executor; // 0.3.5

pub fn exercise() {
    executor::block_on(example());
}

#[inline(never)]
async fn example() {
    canary()
}

#[inline(never)]
fn canary() {}

如果查看此程序集，则将看到编译器如何实现异步功能。 async函数返回一个实现 impl Future的类型，该类型在后台由生成器提供动力:

playground::example:
    subq    $24, %rsp
    movb    $0, 16(%rsp)
    movzbl  16(%rsp), %edi
    callq   *core::future::from_generator@GOTPCREL(%rip)
    movb    %al, 23(%rsp)
    movb    23(%rsp), %al
    movb    %al, 8(%rsp)
    movb    8(%rsp), %al
    addq    $24, %rsp
    retq

异步函数的实际主体移到了生成器中，生成器恰好使用了名称 {{closure}}:

playground::example::{{closure}}:
;; Lots of instructions removed
    movq    playground::canary@GOTPCREL(%rip), %rcx
    callq   *%rcx
    jmp .LBB20_2
;; Even more removed

因此，您可以在该生成的函数上设置一个断点:

(lldb) br set -r '.*example.*closure.*'

(lldb) r
Process 28101 launched: '/tmp/f/target/debug/f' (x86_64)
Process 28101 stopped
* thread #1, queue = 'com.apple.main-thread', stop reason = breakpoint 1.1
    frame #0: 0x0000000100000ab0 f`f::example::_$u7b$$u7b$closure$u7d$$u7d$::h2b30ad777e7395f3((null)=(pointer = 0x00007ffeefbff328), (null)=ResumeTy @ 0x00007ffeefbff070) at main.rs:8:20
   5    }
   6
   7    #[inline(never)]
-> 8    async fn example() {
   9        canary()
   10   }
   11
Target 0: (f) stopped.

您还可以在所需的行上设置一个断点:

(lldb) breakpoint set --file /private/tmp/f/src/main.rs --line 9

(lldb) r
Process 28113 launched: '/tmp/f/target/debug/f' (x86_64)
Process 28113 stopped
* thread #1, queue = 'com.apple.main-thread', stop reason = breakpoint 1.1
    frame #0: 0x0000000100000ad8 f`f::example::_$u7b$$u7b$closure$u7d$$u7d$::h2b30ad777e7395f3((null)=(pointer = 0x00007ffeefbff328), (null)=ResumeTy @ 0x00007ffeefbff070) at main.rs:9:5
   6
   7    #[inline(never)]
   8    async fn example() {
-> 9        canary()
   10   }
   11
   12   #[inline(never)]
Target 0: (f) stopped.

也可以看看:

What is the concrete type of a future returned from `async fn`?

What is the purpose of async/await in Rust?

Unable to set a breakpoint on main while debugging a program compiled with Rust 1.10 with GDB

How to use a debugger like GDB or LLDB to debug a crate in Rust?

Can I set an LLDB breakpoint when multiple Rust source files share the same name?