从源码的角度去学习 Go slice

发表于 3年以前 | 总阅读数：307 次

slice是golang开发中最常用到的内置类型之一。与数组相比，它具有长度不固定、可动态添加元素的特性。

# 版本说明

本文涉及到的源码解析部分来源于go官方的1.15.8版本。

# 定义

slice在golang的runtime层面定义如下：

type slice struct {
    array unsafe.Pointer // 数组元素
    len   int // 长度
    cap   int // 容量
}

slice包括3个字段：

array：表示当前slice存放的数组元素。
len：表示当前slice已经使用的长度。
cap：表示当前slice的总容量，即最大能够容纳的元素个数。

如图所示，slice的动态特性正是基于这样的数据结构：一方面，记录已经使用的元素个数；另一方面，元素存放在有容量上限的底层数组中。

# 创建slice

slice的创建需要借助golang builtin包中的make函数：

// The make built-in function allocates and initializes an object of type
// slice, map, or chan (only). Like new, the first argument is a type, not a
// value. Unlike new, make's return type is the same as the type of its
// argument, not a pointer to it. The specification of the result depends on
// the type:
//    Slice: The size specifies the length. The capacity of the slice is
//    equal to its length. A second integer argument may be provided to
//    specify a different capacity; it must be no smaller than the
//    length. For example, make([]int, 0, 10) allocates an underlying array
//    of size 10 and returns a slice of length 0 and capacity 10 that is
//    backed by this underlying array.
//    Map: An empty map is allocated with enough space to hold the
//    specified number of elements. The size may be omitted, in which case
//    a small starting size is allocated.
//    Channel: The channel's buffer is initialized with the specified
//    buffer capacity. If zero, or the size is omitted, the channel is
//    unbuffered.
func make(t Type, size ...IntegerType) Type

make在golang中是一个创建内置类型的通用函数，不仅仅是slice，包括chan、map都需要借助make函数来创建。slice的创建主要包括如下两种形式：

nums := make([]int, 10) // 创建长度和容量均为10的int slice
nums := make([]int, 0, 10) // 创建长度为0，容量为10的int slice

以下面的代码为例：

package main

import (
    "fmt"
)

func main() {
    nums := make([]int, 0, 10)
    nums = append(nums, 0)
    fmt.Println(nums)
}

让我们通过go的官方工具来查看汇编结果：

$ go tool compile -S main.go

"".main STEXT size=217 args=0x0 locals=0x58 funcid=0x0
    0x0000 00000 (main.go:7)    TEXT    "".main(SB), ABIInternal, $88-0
    0x0000 00000 (main.go:7)    MOVQ    (TLS), CX
    0x0009 00009 (main.go:7)    CMPQ    SP, 16(CX)
    0x000d 00013 (main.go:7)    PCDATA  $0, $-2
    0x000d 00013 (main.go:7)    JLS 207
    0x0013 00019 (main.go:7)    PCDATA  $0, $-1
    0x0013 00019 (main.go:7)    SUBQ    $88, SP
    0x0017 00023 (main.go:7)    MOVQ    BP, 80(SP)
    0x001c 00028 (main.go:7)    LEAQ    80(SP), BP
    0x0021 00033 (main.go:7)    FUNCDATA    $0, gclocals·33cdeccccebe80329f1fdbee7f5874cb(SB)
    0x0021 00033 (main.go:7)    FUNCDATA    $1, gclocals·f207267fbf96a0178e8758c6e3e0ce28(SB)
    0x0021 00033 (main.go:7)    FUNCDATA    $2, "".main.stkobj(SB)
    0x0021 00033 (main.go:8)    LEAQ    type.int(SB), AX
    0x0028 00040 (main.go:8)    MOVQ    AX, (SP)
    0x002c 00044 (main.go:8)    MOVQ    $0, 8(SP)
    0x0035 00053 (main.go:8)    MOVQ    $10, 16(SP)
    0x003e 00062 (main.go:8)    PCDATA  $1, $0
    0x003e 00062 (main.go:8)    NOP
    0x0040 00064 (main.go:8)    CALL    runtime.makeslice(SB) # 从这一行我们可以看出slice的创建最终底层实现是runtime.makeslice函数
    0x0045 00069 (main.go:8)    MOVQ    24(SP), AX
    0x004a 00074 (main.go:9)    MOVQ    $0, (AX)
    0x0051 00081 (main.go:10)   MOVQ    AX, (SP)
    0x0055 00085 (main.go:10)   MOVQ    $1, 8(SP)
    0x005e 00094 (main.go:10)   MOVQ    $10, 16(SP)
    0x0067 00103 (main.go:10)   CALL    runtime.convTslice(SB)
    0x006c 00108 (main.go:10)   MOVQ    24(SP), AX
    0x0071 00113 (main.go:10)   XORPS   X0, X0
    0x0074 00116 (main.go:10)   MOVUPS  X0, ""..autotmp_13+64(SP)
    0x0079 00121 (main.go:10)   LEAQ    type.[]int(SB), CX
    0x0080 00128 (main.go:10)   MOVQ    CX, ""..autotmp_13+64(SP)
    0x0085 00133 (main.go:10)   MOVQ    AX, ""..autotmp_13+72(SP)
    ... 省略不相关部分

PS：请读者先不要迷失在汇编代码的细节中，目前我们只需要关注"(main.go:8)“对应底层实现是调用go的runtime.makeslice函数，了解这一点即可。

因此，我们进一步去翻阅相关的go源码：

func makeslice(et *_type, len, cap int) unsafe.Pointer { // _type是go所有类型在runtime层面的表示形式
    mem, overflow := math.MulUintptr(et.size, uintptr(cap)) // 预期内存开销是：元素类型长度x元素个数，同时判断是否算术溢出
    if overflow || mem > maxAlloc || len < 0 || len > cap {
        // NOTE: Produce a 'len out of range' error instead of a
        // 'cap out of range' error when someone does make([]T, bignumber).
        // 'cap out of range' is true too, but since the cap is only being
        // supplied implicitly, saying len is clearer.
        // See golang.org/issue/4085.
        mem, overflow := math.MulUintptr(et.size, uintptr(len))
        if overflow || mem > maxAlloc || len < 0 {
            panicmakeslicelen()
        }
        panicmakeslicecap()
    }

    return mallocgc(mem, et, true) // 申请内存块
}

makeslice函数计算出所需的内存开销之后，会检查是否算术溢出，紧接着通过mallocgc函数去申请内存块。PS：由于mallocgc涉及到比较多的go内存管理相关的知识点，因此不在本文展开。

至此，slice就完成了内存申请。

# 复制slice

slice的复制可以借助golang builtin包中的copy函数：

// The copy built-in function copies elements from a source slice into a
// destination slice. (As a special case, it also will copy bytes from a
// string to a slice of bytes.) The source and destination may overlap. Copy
// returns the number of elements copied, which will be the minimum of
// len(src) and len(dst).
func copy(dst, src []Type) int

以下面的代码为例：

package main

import (
    "fmt"
)

func main() {
    src := []int{ 1, 2, 3 }
    tar := make([]int, 2)
    copy(tar, src)
    fmt.Println(tar)
}

让我们通过go的官方工具来查看汇编结果：

$ go tool compile -S main.go"".main STEXT size=261 args=0x0 locals=0x70 funcid=0x0    0x0000 00000 (main.go:7)    TEXT    "".main(SB), ABIInternal, $112-0   0x0000 00000 (main.go:7)    MOVQ    (TLS), CX   0x0009 00009 (main.go:7)    CMPQ    SP, 16(CX)  0x000d 00013 (main.go:7)    PCDATA  $0, $-2   0x000d 00013 (main.go:7)    JLS 249 0x0013 00019 (main.go:7)    PCDATA  $0, $-1   0x0013 00019 (main.go:7)    SUBQ    $112, SP   0x0017 00023 (main.go:7)    MOVQ    BP, 104(SP) 0x001c 00028 (main.go:7)    LEAQ    104(SP), BP 0x0021 00033 (main.go:7)    FUNCDATA    $0, gclocals·33cdeccccebe80329f1fdbee7f5874cb(SB)  0x0021 00033 (main.go:7)    FUNCDATA    $1, gclocals·f207267fbf96a0178e8758c6e3e0ce28(SB)  0x0021 00033 (main.go:7)    FUNCDATA    $2, "".main.stkobj(SB) 0x0021 00033 (main.go:8)    MOVQ    $0, ""..autotmp_12+64(SP)  0x002a 00042 (main.go:8)    XORPS   X0, X0  0x002d 00045 (main.go:8)    MOVUPS  X0, ""..autotmp_12+72(SP)   0x0032 00050 (main.go:8)    MOVQ    $1, ""..autotmp_12+64(SP)  0x003b 00059 (main.go:8)    MOVQ    $2, ""..autotmp_12+72(SP)  0x0044 00068 (main.go:8)    MOVQ    $3, ""..autotmp_12+80(SP)  0x004d 00077 (main.go:9)    LEAQ    type.int(SB), AX    0x0054 00084 (main.go:9)    MOVQ    AX, (SP)    0x0058 00088 (main.go:9)    MOVQ    $2, 8(SP)  0x0061 00097 (main.go:9)    MOVQ    $3, 16(SP) 0x006a 00106 (main.go:9)    LEAQ    ""..autotmp_12+64(SP), AX   0x006f 00111 (main.go:9)    MOVQ    AX, 24(SP)  0x0074 00116 (main.go:9)    PCDATA  $1, $0    0x0074 00116 (main.go:9)    CALL    runtime.makeslicecopy(SB) # 调用runtime的makeslicecopy函数   0x0079 00121 (main.go:9)    MOVQ    32(SP), AX  0x007e 00126 (main.go:11)   MOVQ    AX, (SP)    0x0082 00130 (main.go:11)   MOVQ    $2, 8(SP)  0x008b 00139 (main.go:11)   MOVQ    $2, 16(SP) 0x0094 00148 (main.go:11)   CALL    runtime.convTslice(SB)  0x0099 00153 (main.go:11)   MOVQ    24(SP), AX  0x009e 00158 (main.go:11)   XORPS   X0, X0  0x00a1 00161 (main.go:11)   MOVUPS  X0, ""..autotmp_17+88(SP)   0x00a6 00166 (main.go:11)   LEAQ    type.[]int(SB), CX  0x00ad 00173 (main.go:11)   MOVQ    CX, ""..autotmp_17+88(SP)   0x00b2 00178 (main.go:11)   MOVQ    AX, ""..autotmp_17+96(SP)   ... 省略不相关部分

通过汇编代码的结果可以看出，copy函数在go的runtime层面是调用了runtime.makeslicecopy函数。因此，我们进一步查看相关源码：

// makeslicecopy allocates a slice of "tolen" elements of type "et",
// then copies "fromlen" elements of type "et" into that new allocation from "from".
func makeslicecopy(et *_type, tolen int, fromlen int, from unsafe.Pointer) unsafe.Pointer { // 参数分别是：数据类型、目标长度、来源长度、来源元素数组
    /*
        计算需要复制的内存块大小：
        1. 目标slice长度 > 来源slice长度，以来源长度为准
        2. 目标slice长度 <= 来源slice长度，以目标长度为准
    */
    var tomem, copymem uintptr
    if uintptr(tolen) > uintptr(fromlen) {
        var overflow bool
        tomem, overflow = math.MulUintptr(et.size, uintptr(tolen))
        if overflow || tomem > maxAlloc || tolen < 0 {
            panicmakeslicelen()
        }
        copymem = et.size * uintptr(fromlen)
    } else {
        // fromlen is a known good length providing and equal or greater than tolen,
        // thereby making tolen a good slice length too as from and to slices have the
        // same element width.
        tomem = et.size * uintptr(tolen)
        copymem = tomem
    }

    /*
        申请内存块
    */ 
    var to unsafe.Pointer
    if et.ptrdata == 0 {
        to = mallocgc(tomem, nil, false)
        if copymem < tomem {
            memclrNoHeapPointers(add(to, copymem), tomem-copymem)
        }
    } else {
        // Note: can't use rawmem (which avoids zeroing of memory), because then GC can scan uninitialized memory.
        to = mallocgc(tomem, et, true)
        if copymem > 0 && writeBarrier.enabled {
            // Only shade the pointers in old.array since we know the destination slice to
            // only contains nil pointers because it has been cleared during alloc.
            bulkBarrierPreWriteSrcOnly(uintptr(to), uintptr(from), copymem)
        }
    }

    /*
        数据竞争检测和支持与内存清理程序的互操作
    */
    if raceenabled {
        callerpc := getcallerpc()
        pc := funcPC(makeslicecopy)
        racereadrangepc(from, copymem, callerpc, pc)
    }
    if msanenabled {
        msanread(from, copymem)
    }

    // 复制内存块
    memmove(to, from, copymem)

    return to
}

小结一下，通过copy函数的底层实现，我们能够知道：

slice的复制是基于复制内存块来完成的。
slice的复制会考虑目标slice的长度，仅会复制不大于目标slice长度的元素。

# 新增元素

给slice新增元素需要借助golang builtin包中的append函数：

// The append built-in function appends elements to the end of a slice. If// it has sufficient capacity, the destination is resliced to accommodate the// new elements. If it does not, a new underlying array will be allocated.// Append returns the updated slice. It is therefore necessary to store the// result of append, often in the variable holding the slice itself://    slice = append(slice, elem1, elem2)//   slice = append(slice, anotherSlice...)// As a special case, it is legal to append a string to a byte slice, like this://    slice = append([]byte("hello "), "world"...)func append(slice []Type, elems ...Type) []Type

日常使用示例如下：

nums := make([]int, 0, 10)
nums = append(nums, 1)
nums = append(nums, 5)
nums = append(nums, 6)

# 删除元素

不同于新增元素，golang中并未内置删除slice指定元素的函数，需要开发者自己去实现。就笔者所了解的删除元素方法主要有如下几种方式：

方法一：创建新的slice切片

func removeElem(src []int, toDel int) []int {
    tar := make([]int, 0, len(src))
    for _, num := range src {
        if num != toDel {
            tar = append(tar, num)
        }
    }

    return tar
}

方法二：复用原有的slice切片

func removeElem(src []int, toDel int) []int {
    tar := src[:0]
    for _, num := range src {
        if num != toDel {
            tar = append(tar, num)
        }
    }

    return tar
}

方法三：复用原有的slice切片，平移剩下的元素

func removeElem(src []int, toDel int) []int {
    for i := 0; i < len(src); i++ {
        if src[i] == toDel {
            src = append(src[:i], src[i+1:]...)
            i--
        }
    }

    return src
}

小结一下，方法一的主要优点是不修改原有slice的数据，仅当不允许修改源slice数据的前提下推荐方法一。其它情况下，请使用方法二或者方法三，性能方面和开销方面都比较优秀。

# 扩容slice

动态扩容是slice最大的特点。我们日常使用slice的过程中，并不会感受到slice的真实容量变化情况，golang底层会帮助我们完成对应的slice扩容。

以下面的代码为例：

package main

import (
    "fmt"
)

func main() {
    nums := make([]int, 0, 2) // 初始设置为2
    nums = append(nums, 1)
    nums = append(nums, 2)
    nums = append(nums, 3) // 触发扩容
    nums = append(nums, 4)
    nums = append(nums, 5)
    fmt.Println(nums)
}

让我们通过go的官方工具来查看汇编结果：

$ go tool compile -S main.go

"".main STEXT size=490 args=0x0 locals=0x60 funcid=0x0
    0x0000 00000 (main.go:7)    TEXT    "".main(SB), ABIInternal, $96-0
    0x0000 00000 (main.go:7)    MOVQ    (TLS), CX
    0x0009 00009 (main.go:7)    CMPQ    SP, 16(CX)
    0x000d 00013 (main.go:7)    PCDATA  $0, $-2
    0x000d 00013 (main.go:7)    JLS 480
    0x0013 00019 (main.go:7)    PCDATA  $0, $-1
    0x0013 00019 (main.go:7)    SUBQ    $96, SP
    0x0017 00023 (main.go:7)    MOVQ    BP, 88(SP)
    0x001c 00028 (main.go:7)    LEAQ    88(SP), BP
    0x0021 00033 (main.go:7)    FUNCDATA    $0, gclocals·33cdeccccebe80329f1fdbee7f5874cb(SB)
    0x0021 00033 (main.go:7)    FUNCDATA    $1, gclocals·f207267fbf96a0178e8758c6e3e0ce28(SB)
    0x0021 00033 (main.go:7)    FUNCDATA    $2, "".main.stkobj(SB)
    0x0021 00033 (main.go:8)    LEAQ    type.int(SB), AX
    0x0028 00040 (main.go:8)    MOVQ    AX, (SP)
    0x002c 00044 (main.go:8)    MOVQ    $0, 8(SP)
    0x0035 00053 (main.go:8)    MOVQ    $2, 16(SP)
    0x003e 00062 (main.go:8)    PCDATA  $1, $0
    0x003e 00062 (main.go:8)    NOP
    0x0040 00064 (main.go:8)    CALL    runtime.makeslice(SB)
    0x0045 00069 (main.go:8)    MOVQ    24(SP), AX
    0x004a 00074 (main.go:9)    MOVQ    $1, (AX)
    0x0051 00081 (main.go:10)   MOVQ    $2, 8(AX)
    0x0059 00089 (main.go:11)   LEAQ    type.int(SB), CX
    0x0060 00096 (main.go:11)   MOVQ    CX, (SP)
    0x0064 00100 (main.go:11)   MOVQ    AX, 8(SP)
    0x0069 00105 (main.go:11)   MOVQ    $2, 16(SP)
    0x0072 00114 (main.go:11)   MOVQ    $2, 24(SP)
    0x007b 00123 (main.go:11)   MOVQ    $3, 32(SP)
    0x0084 00132 (main.go:11)   CALL    runtime.growslice(SB) # 调用runtime的growslice函数
    0x0089 00137 (main.go:11)   MOVQ    40(SP), AX
    0x008e 00142 (main.go:11)   MOVQ    56(SP), CX
    0x0093 00147 (main.go:11)   MOVQ    48(SP), DX
    0x0098 00152 (main.go:11)   MOVQ    $3, 16(AX)
    0x00a0 00160 (main.go:11)   INCQ    DX
    0x00a3 00163 (main.go:12)   LEAQ    1(DX), BX
    0x00a7 00167 (main.go:12)   CMPQ    CX, BX
    0x00aa 00170 (main.go:12)   JCS 403
    0x00b0 00176 (main.go:12)   MOVQ    $4, (AX)(DX*8)
    0x00b8 00184 (main.go:13)   LEAQ    1(BX), DX
    0x00bc 00188 (main.go:13)   NOP
    0x00c0 00192 (main.go:13)   CMPQ    CX, DX
    0x00c3 00195 (main.go:13)   JCS 325
    0x00c9 00201 (main.go:13)   MOVQ    $5, (AX)(BX*8)
    0x00d1 00209 (main.go:14)   MOVQ    AX, (SP)
    0x00d5 00213 (main.go:14)   MOVQ    DX, 8(SP)
    0x00da 00218 (main.go:14)   MOVQ    CX, 16(SP)
    0x00df 00223 (main.go:14)   NOP
    0x00e0 00224 (main.go:14)   CALL    runtime.convTslice(SB)
    0x00e5 00229 (main.go:14)   MOVQ    24(SP), AX
    ... 省略不相关部分

因此，我们进一步查看相关源码：

func growslice(et *_type, old slice, cap int) slice {
    if raceenabled {
        callerpc := getcallerpc()
        racereadrangepc(old.array, uintptr(old.len*int(et.size)), callerpc, funcPC(growslice))
    }
    if msanenabled {
        msanread(old.array, uintptr(old.len*int(et.size)))
    }

    if cap < old.cap {
        panic(errorString("growslice: cap out of range"))
    }

    if et.size == 0 {
        // append should not create a slice with nil pointer but non-zero len.
        // We assume that append doesn't need to preserve old.array in this case.
        return slice{unsafe.Pointer(&zerobase), old.len, cap}
    }

    /*
        扩容规则：
        1. 长度 < 1024的情况下，扩容2倍
        2. 长度 > 1024的情况下，扩容1.25倍
    */ 

    newcap := old.cap
    doublecap := newcap + newcap
    if cap > doublecap {
        newcap = cap
    } else {
        if old.len < 1024 {
            newcap = doublecap
        } else {
            // Check 0 < newcap to detect overflow
            // and prevent an infinite loop.
            for 0 < newcap && newcap < cap {
                newcap += newcap / 4
            }
            // Set newcap to the requested cap when
            // the newcap calculation overflowed.
            if newcap <= 0 {
                newcap = cap
            }
        }
    }

    /*
        内存对齐操作，对齐之后的容量相比于上述规则来说会有所偏差！
    */
    var overflow bool
    var lenmem, newlenmem, capmem uintptr
    // Specialize for common values of et.size.
    // For 1 we don't need any division/multiplication.
    // For sys.PtrSize, compiler will optimize division/multiplication into a shift by a constant.
    // For powers of 2, use a variable shift.
    switch {
    case et.size == 1:
        lenmem = uintptr(old.len)
        newlenmem = uintptr(cap)
        capmem = roundupsize(uintptr(newcap))
        overflow = uintptr(newcap) > maxAlloc
        newcap = int(capmem)
    case et.size == sys.PtrSize:
        lenmem = uintptr(old.len) * sys.PtrSize
        newlenmem = uintptr(cap) * sys.PtrSize
        capmem = roundupsize(uintptr(newcap) * sys.PtrSize)
        overflow = uintptr(newcap) > maxAlloc/sys.PtrSize
        newcap = int(capmem / sys.PtrSize)
    case isPowerOfTwo(et.size):
        var shift uintptr
        if sys.PtrSize == 8 {
            // Mask shift for better code generation.
            shift = uintptr(sys.Ctz64(uint64(et.size))) & 63
        } else {
            shift = uintptr(sys.Ctz32(uint32(et.size))) & 31
        }
        lenmem = uintptr(old.len) << shift
        newlenmem = uintptr(cap) << shift
        capmem = roundupsize(uintptr(newcap) << shift)
        overflow = uintptr(newcap) > (maxAlloc >> shift)
        newcap = int(capmem >> shift)
    default:
        lenmem = uintptr(old.len) * et.size
        newlenmem = uintptr(cap) * et.size
        capmem, overflow = math.MulUintptr(et.size, uintptr(newcap))
        capmem = roundupsize(capmem)
        newcap = int(capmem / et.size)
    }

    // The check of overflow in addition to capmem > maxAlloc is needed
    // to prevent an overflow which can be used to trigger a segfault
    // on 32bit architectures with this example program:
    //
    // type T [1<<27 + 1]int64
    //
    // var d T
    // var s []T
    //
    // func main() {
    //   s = append(s, d, d, d, d)
    //   print(len(s), "\n")
    // }
    if overflow || capmem > maxAlloc {
        panic(errorString("growslice: cap out of range"))
    }

    /*
        分配内存块
    */
    var p unsafe.Pointer
    if et.ptrdata == 0 {
        p = mallocgc(capmem, nil, false)
        // The append() that calls growslice is going to overwrite from old.len to cap (which will be the new length).
        // Only clear the part that will not be overwritten.
        memclrNoHeapPointers(add(p, newlenmem), capmem-newlenmem)
    } else {
        // Note: can't use rawmem (which avoids zeroing of memory), because then GC can scan uninitialized memory.
        p = mallocgc(capmem, et, true)
        if lenmem > 0 && writeBarrier.enabled {
            // Only shade the pointers in old.array since we know the destination slice p
            // only contains nil pointers because it has been cleared during alloc.
            bulkBarrierPreWriteSrcOnly(uintptr(p), uintptr(old.array), lenmem-et.size+et.ptrdata)
        }
    }

    /*
        把旧slice的内容复制到新slice中
    */
    memmove(p, old.array, lenmem)

    return slice{p, old.len, newcap}
}

小结一下，通过growslice函数的底层实现，我们能够知道：

append操作在golang编译结果中会转化成runtime.growslice函数，对上层透明，因而开发者无需关心slice底层容量大小的问题。
slice触发扩容操作会创建新的容量数组，将旧的slice内容复制过去，开发者需要关注有多个变量引用同一个slice且发生扩容的情况。
slice的扩容原则是：对于长度 < 1024的情况下，2倍增长；对于长度 > 1024的情况下，1.25倍增长。但由于存在内存对齐，slice的容量在扩容结束后会有所偏差！

# 总结

本文详细介绍了Go的内置类型slice，以常见的代码为例，通过go官方工具的汇编结果解析了底层实现。另一方面，本文从源码角度得出一些开发者较为容易迷惑的语法问题，例如slice的复制长度问题、slice扩容之后的底层数组更替问题、slice扩容容量大小问题等等。

总的来说，源码学习是一条漫漫长路。笔者认为开发者既不应该无视源码而只靠背诵一些结论来学习语言，也不应该过分关注源码细节导致无从入手。本文从slice的源码中，也牵扯出一些未能深入解析的概念：Go的runtime、Plan 9汇编、内存对齐等，关于这些概念的进一步解析则会随着笔者的深入学习而逐步完善，在此也希望能与读者共勉！