gdb golang 檢視iface 內部結構

牙小木木發表於2021-11-11
Golang

環境說明

macOs bigSur 11.4
GNU gdb (GDB) 10.2

程式碼準備

package main

type Ner interface {
    a()
    b(int)
    c(string) string
}

type N int

func (N) a() {
}

func (*N) b(i int) {
    return
}

func (*N) c(s string) string {
    return "c"
}

func main() {
    var n N
    var t Ner = &n
    t.a()
}

命令執行

go build -gcflags "-N -l" -ldflags=-compressdwarf=false main.go
gdb main

正常輸出

注意必須要有：Loading Go Runtime support.

deMacBook-Pro:debugGDB de$ gdb main
GNU gdb (GDB) 10.2
Copyright (C) 2021 Free Software Foundation, Inc.
License GPLv3+: GNU GPL version 3 or later <http://gnu.org/licenses/gpl.html>
This is free software: you are free to change and redistribute it.
There is NO WARRANTY, to the extent permitted by law.
Type "show copying" and "show warranty" for details.
This GDB was configured as "x86_64-apple-darwin20.3.0".
Type "show configuration" for configuration details.
For bug reporting instructions, please see:
<https://www.gnu.org/software/gdb/bugs/>.
Find the GDB manual and other documentation resources online at:
    <http://www.gnu.org/software/gdb/documentation/>.

For help, type "help".
Type "apropos word" to search for commands related to "word"...
Reading symbols from main...
Loading Go Runtime support.
(gdb)
  1. 設定斷點（在第25行），然後執行
(gdb) b main.go:25

Loading Go Runtime support.
(gdb) b main.go:25
Breakpoint 1 at 0x1054d98: file /Users/didi/GolandProjects/goLarnNote/Chapter7/Iface/debugGDB/main.go, line 25.
(gdb) run
Starting program: /Users/didi/GolandProjects/goLarnNote/Chapter7/Iface/debugGDB/main 
[New Thread 0x2603 of process 72590]
[New Thread 0x1a03 of process 72590]
warning: unhandled dyld version (17)
[New Thread 0x2403 of process 72590]
[New Thread 0x2507 of process 72590]
[New Thread 0x2203 of process 72590]

Thread 2 hit Breakpoint 1, main.main () at /Users/didi/GolandProjects/goLarnNote/Chapter7/Iface/debugGDB/main.go:25
25              t.a()
  1. 檢視資訊並列印
(gdb) info locals
t = {tab = 0x1076b60 <N,main.Ner>, data = 0xc00003c748}
n = 0
(gdb) set print pretty on
(gdb) p *t.tab.inter
$10 = {
  typ = {
    size = 16,
    ptrdata = 16,
    hash = 1801897693,
    tflag = 7 '\a',
    align = 8 '\b',
    fieldAlign = 8 '\b',
    kind = 20 '\024',
    equal = {void (void *, void *, bool *)} 0x105b818 <type.*+26936>,
    gcdata = 0x1065b18 <func.*+254> "\002",
    str = 2790,
    ptrToThis = 9664
  },
  pkgpath = {
    bytes = 0x105500a <type.*+298> ""
  },
  mhdr = []runtime.imethod = {{
      name = 8,
      ityp = 15552
    }, {
      name = 11,
--Type <RET> for more, q to quit, c to continue without paging--

(gdb) ptype t
type = struct runtime.iface {
    runtime.itab *tab;
    void *data;
}
(gdb) p t
$2 = {tab = 0x1076b60 <N,main.Ner>, data = 0xc00003c748}

(gdb) ptype t.tab._type
type = struct runtime._type {
    uintptr size;
    uintptr ptrdata;
    uint32 hash;
    runtime.tflag tflag;
    uint8 align;
    uint8 fieldAlign;
    uint8 kind;
    func(unsafe.Pointer, unsafe.Pointer) bool equal;
    uint8 *gcdata;
--Type <RET> for more, q to quit, c to continue without paging--

後續todo

結合iface，eface的結構來剖析介面判等 等系列問題

參考資料

gdb-debugger-with-go

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