本文介绍工具 LLDB 的初步使用
Rust 会使用 DWARF 格式在 binary 中嵌入调试信息，所以可以使用一些通用的调试工具，比如 GDB 和 LLDB。Rust 提供了 rust-gdb 和 rust-lldb 两个命令用于调试，其相比原生的 gdb 和 lldb 添加了一些方便调试的脚本
下面来初步的了解 rust-lldb 的使用，rustup 会安装 rust-lldb，但不会安装 lldb，需要自行安装
LLDB 的命令结构如下
<noun> <verb> [-options [option-value]] [argument [argument...]]
本文所使用的代码如下:
fn binary_search(nums: Vec<i32>, target: i32) -> i32 {
let mut size = nums.len();
if size == 0 {
return -1;
}
let mut base = 0usize;
while size > 1 {
let half = size / 2;
let mid = base + half;
if nums[mid] <= target {
base = mid;
}
size = size - half;
}
if nums[base] == target {
return base as i32;
}
return -1;
}
fn main() {
assert_eq!(binary_search(vec![1, 4, 7, 10, 16, 19], 10), 3);
}
cargo build 默认会以 debug 模式进行构建，所以含有用于调试的 symbol，需要注意的是 cargo install 会以 release 模式构建，需要 cargo install --debug
通过 rust-lldb 命令加载可执行文件(或者在 REPL 中通过 file 载入)，进入 LLDB 的 REPL。比如
rust-lldb target/debug/<bin-name> first_arg
启动时会显示
(lldb) settings set -- target.run-args "first_arg"
字样，参数会存在 target.run-args 中，可以在 REPL 中重置命令行参数
(lldb) settings set target.run-args "arg1"
(lldb) settings show target.run-args
target.run-args (array of strings) =
[0]: "arg1"
(lldb) settings append target.run-args "arg2"
(lldb) settings show target.run-args
target.run-args (array of strings) =
[0]: "arg1"
[1]: "arg2"
gui 命令可以进入 GUI，可以借助 voltron 获得更改的体验
通过 b 命令来设置断点。b 命令是对于 GDB 中 break 命令的模拟，并不是 LLDB 中的 breakpoint 的 alias。breakpoint set -n <func name> 设置支持补全，breakpoint set -f <文件路径>--line 15 在指定的行设置断点
(lldb) b binary_search
Breakpoint 1: where = b`b::binary_search::hcb6e4fa332e0db67 + 13 at main.rs:2, address = 0x00000000000049bd
(lldb) b
Current breakpoints:
1: name = 'binary_search', locations = 1
1.1: where = b`b::binary_search::hcb6e4fa332e0db67 + 13 at main.rs:2, address = b[0x00000000000049bd], unresolved, hit count = 0
2: name = 'binary_s', locations = 0 (pending)
3: name = 'binary_search', locations = 1
3.1: where = b`b::binary_search::hcb6e4fa332e0db67 + 13 at main.rs:2, address = b[0x00000000000049bd], unresolved, hit count = 0
(lldb) breakpoint delete 2
1 breakpoints deleted; 0 breakpoint locations disabled.
通过 r 命令来运行程序
(lldb) r
There is a running process, kill it and restart?: [Y/n] y
Process 12494 launched: '/root/T/b/target/debug/b' (x86_64)
Process 12494 stopped
* thread #1, name = 'b', stop reason = breakpoint 1.1
frame #0: 0x00005555555589bd b`b::binary_search::hcb6e4fa332e0db67(nums=vec![1, 4, 7, 10, 16, 19], target=10) at main.rs:2
1 fn binary_search(nums: Vec<i32>, target: i32) -> i32 {
-> 2 let mut size = nums.len();
3
4 if size == 0 {
5 return -1;
6 }
7
通过 frame variable 可以看到当前栈中的变量
(lldb) frame variable
(alloc::vec::Vec<int>) nums = vec![1, 4, 7, 10, 16, 19]
(int) target = 10
通过 n 进行单步调试
(lldb) n
Process 20123 stopped
* thread #1, name = 'b', stop reason = step over
frame #0: 0x00005555555589df b`b::binary_search::hcb6e4fa332e0db67(nums=vec![1, 4, 7, 10, 16, 19], target=10) at main.rs:4
1 fn binary_search(nums: Vec<i32>, target: i32) -> i32 {
2 let mut size = nums.len();
3
-> 4 if size == 0 {
5 return -1;
6 }
7
(lldb) frame variable
(alloc::vec::Vec<int>) nums = vec![1, 4, 7, 10, 16, 19]
(int) target = 10
(unsigned long) size = 6
这都是模拟的 GDB 的命令族。LLDB 原生的则是
(lldb) thead select id
(lldb) thread step-in // The same as gdb's "step" or "s"
(lldb) thread step-over // The same as gdb's "next" or "n"
(lldb) thread step-out // The same as gdb's "finish" or "f"
在断点处可以设置命令，比如直接打印堆栈
(lldb) breakpoint command add 1
Enter your debugger command(s). Type 'DONE' to end.
> bt
> DONE
也可以直接通过 --command 参数设置
一个小例子，在 half == 3 条件成立的时候打印堆栈信息
(lldb) list main.rs:10
10
11 while size > 1 {
12 let half = size / 2;
13 let mid = base + half;
14
15 if nums[mid] <= target {
16 base = mid;
17 }
18 size = size - half;
19 }
20
(lldb) breakpoint set -c "half == 3" -f main.rs -l 13 -C bt
Breakpoint 1: where = b`b::binary_search::hfce4ad2766a2fe8f + 166 at main.rs:13, address = 0x0000000000004a56
(lldb) r
Process 31253 launched: '/root/T/b/target/debug/b' (x86_64)
(lldb) bt
* thread #1, name = 'b', stop reason = breakpoint 1.1
* frame #0: 0x0000555555558a56 b`b::binary_search::hfce4ad2766a2fe8f(nums=vec![1, 4, 7, 10, 16, 19], target=10) at main.rs:13
frame #1: 0x0000555555558b90 b`b::main::he42792ea9d7cc77a at main.rs:29
frame #2: 0x00005555555582c0 b`std::rt::lang_start::_$u7b$$u7b$closure$u7d$$u7d$::h36f6beb6917ae1e7 at rt.rs:74
frame #3: 0x0000555555561743 b`std::panicking::try::do_call::h4f8262c35e4e88a2 [inlined] std::rt::lang_start_internal::_$u7b$$u7b$closure$u7d$$u7d$::h10f59d0290367560 at rt.rs:59
frame #4: 0x0000555555561737 b`std::panicking::try::do_call::h4f8262c35e4e88a2 at panicking.rs:307
frame #5: 0x000055555556ebfa b`__rust_maybe_catch_panic at lib.rs:102
frame #6: 0x0000555555562246 b`std::rt::lang_start_internal::ha81f57a8465b4dcb [inlined] std::panicking::try::h8abdfbcaa376c6de at panicking.rs:286
frame #7: 0x000055555556220b b`std::rt::lang_start_internal::ha81f57a8465b4dcb [inlined] std::panic::catch_unwind::hcc1db352380c01f1 at panic.rs:398
frame #8: 0x000055555556220b b`std::rt::lang_start_internal::ha81f57a8465b4dcb at rt.rs:58
frame #9: 0x0000555555558299 b`std::rt::lang_start::h1bce8d1d740917a0(main=&0x555555558b30, argc=1, argv=&0x7fffffffe3c8) at rt.rs:74
frame #10: 0x0000555555558f1a b`main + 42
frame #11: 0x00007ffff7dc9223 libc.so.6`__libc_start_main + 243
frame #12: 0x000055555555817e b`_start + 46
Process 31253 stopped
* thread #1, name = 'b', stop reason = breakpoint 1.1
frame #0: 0x0000555555558a56 b`b::binary_search::hfce4ad2766a2fe8f(nums=vec![1, 4, 7, 10, 16, 19], target=10) at main.rs:13
10
11 while size > 1 {
12 let half = size / 2;
-> 13 let mid = base + half;
14
15 if nums[mid] <= target {
16 base = mid;
可以通过 watch 来监控变量的变化
(lldb) list main.rs:10
10
11 while size > 1 {
12 let half = size / 2;
13 let mid = base + half;
14
15 if nums[mid] <= target {
16 base = mid;
17 }
18 size = size - half;
19 }
20
(lldb) breakpoint set -f main.rs -l 11
Breakpoint 1: where = b`b::binary_search::hfce4ad2766a2fe8f + 88 at main.rs:11, address = 0x0000000000004a08
(lldb) r
Process 1997 launched: '/root/T/b/target/debug/b' (x86_64)
Process 1997 stopped
* thread #1, name = 'b', stop reason = breakpoint 1.1
frame #0: 0x0000555555558a08 b`b::binary_search::hfce4ad2766a2fe8f(nums=vec![1, 4, 7, 10, 16, 19], target=10) at main.rs:11
8
9 let mut base = 0usize;
10
-> 11 while size > 1 {
12 let half = size / 2;
13 let mid = base + half;
14
(lldb) watch set var base
Watchpoint created: Watchpoint 1: addr = 0x7fffffffdec0 size = 8 state = enabled type = w
declare @ '/root/T/b/src/main.rs:9'
watchpoint spec = 'base'
new value: 0
(lldb) c
Process 1997 resuming
Watchpoint 1 hit:
old value: 0
new value: 3
Process 1997 stopped
* thread #1, name = 'b', stop reason = watchpoint 1
frame #0: 0x0000555555558aa8 b`b::binary_search::hfce4ad2766a2fe8f(nums=vec![1, 4, 7, 10, 16, 19], target=10) at main.rs:18
15 if nums[mid] <= target {
16 base = mid;
17 }
-> 18 size = size - half;
19 }
20
21 if nums[base] == target {
expr 命令可以对表达式求值
lldb) frame variable
(unsigned long) size = 24
(unsigned long) align = 4
(lldb) expr size == 24
(bool) $0 = true