[英]How to watch the init of the go map
I use the delve to debug galang code in vscode.我使用 delve 调试 vscode 中的 galang 代码。 I want to use the delve to see the the creation of the golang map,and I create a breakpoint when use the make function to init the map,but it just cannot step into.
我想使用 delve 来查看 golang map 的创建,我在使用 make function 初始化 map 时创建了一个断点,但它无法进入。
You can use delve to debug the runtime, however you will need to get familiar with the dlv
command line interface (without using a GUI).您可以使用 delve 调试运行时,但是您需要熟悉
dlv
命令行界面(不使用 GUI)。
I will be using the following program as an example:我将使用以下程序作为示例:
package main
func main() {
abc := make(map[string]int)
abc["a"] = 1
abc["b"] = 2
abc["c"] = 2
fmt.Println(abc)
}
We can ask delve to build and debug our program with the dlv debug
command.我们可以使用
dlv debug
命令让 delve 构建和调试我们的程序。 This will drop us into the interactive debugger.这将使我们进入交互式调试器。
One of the things that makes maps "fun" to debug is that the compiler can create maps in different ways.使地图调试“有趣”的一件事是编译器可以以不同的方式创建地图。 We first need to know which functions the compiler is using to create a map(can be several depending on map size).
我们首先需要知道编译器使用哪些函数来创建映射(根据 map 的大小,可以是多个)。 We will ask delve to disassemble the main func with the
disassemble -l main.main
command:我们将要求 delve 使用
disassemble -l main.main
命令反汇编 main 函数:
(dlv) disassemble -l main.main
TEXT main.main(SB) /home/caveman/Downloads/test/main.go
main.go:7 0x4b6860 64488b0c25f8ffffff mov rcx, qword ptr fs:[0xfffffff8]
main.go:7 0x4b6869 488d4424f0 lea rax, ptr [rsp-0x10]
main.go:7 0x4b686e 483b4110 cmp rax, qword ptr [rcx+0x10]
main.go:7 0x4b6872 0f8668010000 jbe 0x4b69e0
main.go:7 0x4b6878 4881ec90000000 sub rsp, 0x90
main.go:7 0x4b687f 4889ac2488000000 mov qword ptr [rsp+0x88], rbp
main.go:7 0x4b6887 488dac2488000000 lea rbp, ptr [rsp+0x88]
main.go:8 0x4b688f e84c86f5ff call $runtime.makemap_small
main.go:8 0x4b6894 488b0424 mov rax, qword ptr [rsp]
main.go:8 0x4b6898 4889442430 mov qword ptr [rsp+0x30], rax
...
Now this looks complicated, but we just have to look for calls to the runtime.现在这看起来很复杂,但我们只需要查找对运行时的调用。 In this case
call $runtime.makemap_small
a call to the makemap_small function.在这种情况下,
call $runtime.makemap_small
调用makemap_small function。
Now that we know this, we need to make a breakpoint in this runtime function.现在我们知道了这一点,我们需要在这个运行时 function 中下一个断点。 We do this using the
break mkSmallMap runtime.makemap_small
command:我们使用
break mkSmallMap runtime.makemap_small
命令执行此操作:
(dlv) break mkSmallMap runtime.makemap_small
Breakpoint mkSmallMap set at 0x40eeef for runtime.makemap_small() /usr/local/go/src/runtime/map.go:292
Now we can start our program by executing the c
(continue) command:现在我们可以通过执行
c
(继续)命令来启动我们的程序:
(dlv) c
> [mkSmallMap] runtime.makemap_small() /usr/local/go/src/runtime/map.go:292 (hits goroutine(1):1 total:1) (PC: 0x40eeef)
Warning: debugging optimized function
287: }
288:
289: // makemap_small implements Go map creation for make(map[k]v) and
290: // make(map[k]v, hint) when hint is known to be at most bucketCnt
291: // at compile time and the map needs to be allocated on the heap.
=> 292: func makemap_small() *hmap {
293: h := new(hmap)
294: h.hash0 = fastrand()
295: return h
296: }
297:
We break in the runtime function itself.我们打破了运行时 function 本身。 The
help
command will help you get started with all the commands you need for debugging. help
命令将帮助您开始使用调试所需的所有命令。 A few basic ones:几个基本的:
If we change the map creation to abc:= make(map[string]int, 100000)
you will see in the disassembly that the runtime function has changed to runtime.makemap
which is likely of more interest to you.如果我们将 map 创建更改为
abc:= make(map[string]int, 100000)
您将在反汇编中看到运行时 function 已更改为runtime.makemap
,您可能更感兴趣。
I hope this gets you going, please leave a comment if you need clarification on anything.我希望这能让你继续前进,如果你需要澄清任何事情,请发表评论。
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