golang interface分析

golang interface

1. 结构定义

示例图

iface define

type iface struct {
    tab  *itab
    data unsafe.Pointer
}

itab define

// layout of Itab known to compilers
// allocated in non-garbage-collected memory
// Needs to be in sync with
// ../cmd/compile/internal/gc/reflect.go:/^func.dumptypestructs.
type itab struct {
    inter  *interfacetype
    _type  *_type
    link   *itab
    bad    int32
    inhash int32      // has this itab been added to hash?
    fun    [1]uintptr // variable sized
}

interfacetype

type interfacetype struct {
    typ     _type
    pkgpath name
    mhdr    []imethod
}

_type define

// Needs to be in sync with ../cmd/compile/internal/ld/decodesym.go:/^func.commonsize,
// ../cmd/compile/internal/gc/reflect.go:/^func.dcommontype and
// ../reflect/type.go:/^type.rtype.
type _type struct {
    size       uintptr
    ptrdata    uintptr // size of memory prefix holding all pointers
    hash       uint32
    tflag      tflag
    align      uint8
    fieldalign uint8
    kind       uint8
    alg        *typeAlg

    // gcdata stores the GC type data for the garbage collector.
    // If the KindGCProg bit is set in kind, gcdata is a GC program.
    // Otherwise it is a ptrmask bitmap. See mbitmap.go for details.

    gcdata    *byte
    str       nameOff
    ptrToThis typeOff
}

2. 测试源码

main.go

3. gdb 调测

(gdb) info locals
b = 200
s = {tab = 0x7ffff7e0f1c0, data = 0xc82000a3b0}
nothing = {_type = 0x4c1360, data = 0xc82000a430}
face = {tab = 0x0, data = 0x0}
any = {_type = 0x4e4a80, data = 0xc82000a3c0}


(gdb) p  *s.tab
$24 = {inter = 0x4dffa0, _type = 0x4e4a80, link = 0x0, bad = 0, unused = 0, fun = {4200784}}

(gdb) p  *s.tab.inter
$26 = {typ = {size = 16, ptrdata = 16, hash = 3958674519, _unused = 0 '\000', align = 8 '\b', fieldalign = 8 '\b', kind = 20 '\024', alg = 0x592770 <runtime.algarray+240>,
    gcdata = 0x537142 "\003\004\005\006\a\b\t\n\r\016\017\020\021\022\025\026\031\032\033\037,568>?Ur\236\237\325\365\377", _string = 0x5161d0, x = 0x4e0018, ptrto = 0x4b6e80,
    zero = 0x539c40 <runtime.zerovalue> ""}, mhdr = {array = 0x4e0000, len = 1, cap = 1}}


(gdb) p  *s.tab._type
$27 = {size = 8, ptrdata = 0, hash = 1148337467, _unused = 0 '\000', align = 8 '\b', fieldalign = 8 '\b', kind = 139 '\213', alg = 0x5926d0 <runtime.algarray+80>,
  gcdata = 0x537140 "\001\002\003\004\005\006\a\b\t\n\r\016\017\020\021\022\025\026\031\032\033\037,568>?Ur\236\237\325\365\377", _string = 0x5161c0, x = 0x4e4ac8, ptrto = 0x4e4d20,
  zero = 0x539c40 <runtime.zerovalue> ""}


(gdb) p  *s.tab.inter.typ._string
$28 = 0x50b930 "main.Stringer"


(gdb) p  *s.tab._type._string
$29 = 0x50b920 "main.Binary"

see

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