golang 常见类型字节数

2022-06-06·2min·李岩

ebpf 分析golang程序时，离不开对参数大小的判断。这里列出来一些基本类型的大小，并通过汇编对应验证函数的方式来肯定判断结果。

信息

这里列出基本类型及其作为参数传递时，占用的空间大小如下表。

类型	长度	说明
指针	8B	64位机为 8Byte, 32位机位4Byte
context	16B	interface 类型。其中，前8B是类型信息，后8B是对象的指针信息
interface	16B	2 个指针，详见draveness-go-interface，或者 runtime/runtime2.go iface/eface 定义
int64	8B	-
int	8B	64位机为 8Byte, 32位机位4Byte
string	16B	8B 地址 + 8B string长度
slice	24B	8B地址 + 8B slice 成员数量 + 8B slice capability
func	8B	func 作为函数参数时，传递的是 func 的地址

需要注意的是，作为函数参数传递时，golang会对参数按照 8B 进行对齐。

验证示例

// main.go
package main

import "context"

type A struct {
	p1 int64
	a  byte
	b  int64
}

type FuncPt func(A)

type InterA interface {
	Echo(A)
}

func CheckPointer(a *A)            {}
func CheckCtx(ctx context.Context) {}
func CheckInterface(inter InterA)  {}
func CheckString(s string)         {}
func CheckSlice(arr []string)      {}
func CheckFunc(fn FuncPt)          {}
func CheckAlign(a byte)            {}
func CheckStruct(a A)              {}
func main()                        {}

对该代码进行汇编:
go build -gcflags "-S" . > main.s 可以得到汇编后的结果，并验证上述类型所占大小的描述。这里推荐下曹大的plan9 汇编入门，里面对golang汇编后的plan9进行了介绍。由其介绍可知，汇编后函数签名后的$x-y指代的是该函数的栈空间以及参数大小（入参+返回参数，go-1.17及之后的版本未验证）。

# command-line-arguments
"".CheckPointer STEXT size=16 args=0x8 locals=0x0 funcid=0x0 leaf
	0x0000 00000 (/Users/liyan/zone/go_learn/param/main.go:17)	TEXT	"".CheckPointer(SB), LEAF|NOFRAME|ABIInternal, $0-8
	0x0000 00000 (/Users/liyan/zone/go_learn/param/main.go:17)	FUNCDATA	ZR, gclocals·2a5305abe05176240e61b8620e19a815(SB)
	0x0000 00000 (/Users/liyan/zone/go_learn/param/main.go:17)	FUNCDATA	$1, gclocals·33cdeccccebe80329f1fdbee7f5874cb(SB)
	0x0000 00000 (/Users/liyan/zone/go_learn/param/main.go:17)	RET	(R30)
	0x0000 c0 03 5f d6 00 00 00 00 00 00 00 00 00 00 00 00  .._.............
"".CheckCtx STEXT size=16 args=0x10 locals=0x0 funcid=0x0 leaf
	0x0000 00000 (/Users/liyan/zone/go_learn/param/main.go:18)	TEXT	"".CheckCtx(SB), LEAF|NOFRAME|ABIInternal, $0-16
	0x0000 00000 (/Users/liyan/zone/go_learn/param/main.go:18)	FUNCDATA	ZR, gclocals·f207267fbf96a0178e8758c6e3e0ce28(SB)
	0x0000 00000 (/Users/liyan/zone/go_learn/param/main.go:18)	FUNCDATA	$1, gclocals·33cdeccccebe80329f1fdbee7f5874cb(SB)
	0x0000 00000 (/Users/liyan/zone/go_learn/param/main.go:18)	RET	(R30)
	0x0000 c0 03 5f d6 00 00 00 00 00 00 00 00 00 00 00 00  .._.............
"".CheckInterface STEXT size=16 args=0x10 locals=0x0 funcid=0x0 leaf
	0x0000 00000 (/Users/liyan/zone/go_learn/param/main.go:19)	TEXT	"".CheckInterface(SB), LEAF|NOFRAME|ABIInternal, $0-16
	0x0000 00000 (/Users/liyan/zone/go_learn/param/main.go:19)	FUNCDATA	ZR, gclocals·f207267fbf96a0178e8758c6e3e0ce28(SB)
	0x0000 00000 (/Users/liyan/zone/go_learn/param/main.go:19)	FUNCDATA	$1, gclocals·33cdeccccebe80329f1fdbee7f5874cb(SB)
	0x0000 00000 (/Users/liyan/zone/go_learn/param/main.go:19)	RET	(R30)
	0x0000 c0 03 5f d6 00 00 00 00 00 00 00 00 00 00 00 00  .._.............
"".CheckString STEXT size=16 args=0x10 locals=0x0 funcid=0x0 leaf
	0x0000 00000 (/Users/liyan/zone/go_learn/param/main.go:20)	TEXT	"".CheckString(SB), LEAF|NOFRAME|ABIInternal, $0-16
	0x0000 00000 (/Users/liyan/zone/go_learn/param/main.go:20)	FUNCDATA	ZR, gclocals·2a5305abe05176240e61b8620e19a815(SB)
	0x0000 00000 (/Users/liyan/zone/go_learn/param/main.go:20)	FUNCDATA	$1, gclocals·33cdeccccebe80329f1fdbee7f5874cb(SB)
	0x0000 00000 (/Users/liyan/zone/go_learn/param/main.go:20)	RET	(R30)
	0x0000 c0 03 5f d6 00 00 00 00 00 00 00 00 00 00 00 00  .._.............
"".CheckSlice STEXT size=16 args=0x18 locals=0x0 funcid=0x0 leaf
	0x0000 00000 (/Users/liyan/zone/go_learn/param/main.go:21)	TEXT	"".CheckSlice(SB), LEAF|NOFRAME|ABIInternal, $0-24
	0x0000 00000 (/Users/liyan/zone/go_learn/param/main.go:21)	FUNCDATA	ZR, gclocals·2a5305abe05176240e61b8620e19a815(SB)
	0x0000 00000 (/Users/liyan/zone/go_learn/param/main.go:21)	FUNCDATA	$1, gclocals·33cdeccccebe80329f1fdbee7f5874cb(SB)
	0x0000 00000 (/Users/liyan/zone/go_learn/param/main.go:21)	RET	(R30)
	0x0000 c0 03 5f d6 00 00 00 00 00 00 00 00 00 00 00 00  .._.............
"".CheckFunc STEXT size=16 args=0x8 locals=0x0 funcid=0x0 leaf
	0x0000 00000 (/Users/liyan/zone/go_learn/param/main.go:22)	TEXT	"".CheckFunc(SB), LEAF|NOFRAME|ABIInternal, $0-8
	0x0000 00000 (/Users/liyan/zone/go_learn/param/main.go:22)	FUNCDATA	ZR, gclocals·2a5305abe05176240e61b8620e19a815(SB)
	0x0000 00000 (/Users/liyan/zone/go_learn/param/main.go:22)	FUNCDATA	$1, gclocals·33cdeccccebe80329f1fdbee7f5874cb(SB)
	0x0000 00000 (/Users/liyan/zone/go_learn/param/main.go:22)	RET	(R30)
	0x0000 c0 03 5f d6 00 00 00 00 00 00 00 00 00 00 00 00  .._.............
"".CheckAlign STEXT size=16 args=0x8 locals=0x0 funcid=0x0 leaf
	0x0000 00000 (/Users/liyan/zone/go_learn/param/main.go:23)	TEXT	"".CheckAlign(SB), LEAF|NOFRAME|ABIInternal, $0-8
	0x0000 00000 (/Users/liyan/zone/go_learn/param/main.go:23)	FUNCDATA	ZR, gclocals·33cdeccccebe80329f1fdbee7f5874cb(SB)
	0x0000 00000 (/Users/liyan/zone/go_learn/param/main.go:23)	FUNCDATA	$1, gclocals·33cdeccccebe80329f1fdbee7f5874cb(SB)
	0x0000 00000 (/Users/liyan/zone/go_learn/param/main.go:23)	RET	(R30)
	0x0000 c0 03 5f d6 00 00 00 00 00 00 00 00 00 00 00 00  .._.............
"".CheckStruct STEXT size=16 args=0x18 locals=0x0 funcid=0x0 leaf
	0x0000 00000 (/Users/liyan/zone/go_learn/param/main.go:24)	TEXT	"".CheckStruct(SB), LEAF|NOFRAME|ABIInternal, $0-24
	0x0000 00000 (/Users/liyan/zone/go_learn/param/main.go:24)	FUNCDATA	ZR, gclocals·33cdeccccebe80329f1fdbee7f5874cb(SB)
	0x0000 00000 (/Users/liyan/zone/go_learn/param/main.go:24)	FUNCDATA	$1, gclocals·33cdeccccebe80329f1fdbee7f5874cb(SB)
	0x0000 00000 (/Users/liyan/zone/go_learn/param/main.go:24)	RET	(R30)
	0x0000 c0 03 5f d6 00 00 00 00 00 00 00 00 00 00 00 00  .._.............
"".main STEXT size=16 args=0x0 locals=0x0 funcid=0x0 leaf
	0x0000 00000 (/Users/liyan/zone/go_learn/param/main.go:26)	TEXT	"".main(SB), LEAF|NOFRAME|ABIInternal, $0-0
	0x0000 00000 (/Users/liyan/zone/go_learn/param/main.go:26)	FUNCDATA	ZR, gclocals·33cdeccccebe80329f1fdbee7f5874cb(SB)
	0x0000 00000 (/Users/liyan/zone/go_learn/param/main.go:26)	FUNCDATA	$1, gclocals·33cdeccccebe80329f1fdbee7f5874cb(SB)
	0x0000 00000 (/Users/liyan/zone/go_learn/param/main.go:28)	RET	(R30)
	0x0000 c0 03 5f d6 00 00 00 00 00 00 00 00 00 00 00 00  .._.............