Go 语言中的系统调用

64位 Linux 上的系统调用

printfgetsfopenreadwriteopenltrace

#include <stdio.h>
/* The well-known "Hello World" */
int main(void) {
    printf("Hello World!\n");
}

ltrace

name1e5s@asgard:~$ gcc test.c 
name1e5s@asgard:~$ ltrace -S ./a.out 
SYS_brk(0)                                                                                                           = 0x55eb2abba000
SYS_access("/etc/ld.so.nohwcap", 00) = -2
SYS_access("/etc/ld.so.preload", 04) = -2
SYS_openat(0xffffff9c, 0x7f2290c00428, 0x80000, 0) = 3
SYS_fstat(3, 0x7ffd2e03aa20) = 0
SYS_mmap(0, 0x21b06, 1, 2)  = 0x7f2290de4000
SYS_close(3) = 0
SYS_access("/etc/ld.so.nohwcap", 00) = -2
SYS_openat(0xffffff9c, 0x7f2290e08dd0, 0x80000, 0) = 3
SYS_read(3, "\177ELF\002\001\001\003", 832) = 832
SYS_fstat(3, 0x7ffd2e03aa80) = 0
SYS_mmap(0, 8192, 3, 34) = 0x7f2290de2000
SYS_mmap(0, 0x3f0ae0, 5, 2050) = 0x7f22907ee000
SYS_mprotect(0x7f22909d5000, 2097152, 0) = 0
SYS_mmap(0x7f2290bd5000, 0x6000, 3, 2066) = 0x7f2290bd5000
SYS_mmap(0x7f2290bdb000, 0x3ae0, 3, 50) = 0x7f2290bdb000
SYS_close(3) = 0
SYS_arch_prctl(4098, 0x7f2290de34c0, 0x7f2290de3e00, 0x7f2290de2988) = 0
SYS_mprotect(0x7f2290bd5000, 16384, 1) = 0
SYS_mprotect(0x55eb28ecf000, 4096, 1) = 0
SYS_mprotect(0x7f2290e06000, 4096, 1) = 0
SYS_munmap(0x7f2290de4000, 137990) = 0
puts("Hello World!" <unfinished ...>
SYS_fstat(1, 0x7ffd2e03b280) = 0
SYS_brk(0) = 0x55eb2abba000
SYS_brk(0x55eb2abdb000) = 0x55eb2abdb000
SYS_write(1, "Hello World!\n", 13Hello World!
) = 13
<... puts resumed> ) = 13
SYS_exit_group(0 <no return ...>
+++ exited (status 0) +++

SYS_amd64 Linux

x86(-64)int 80sysentersyscallint 80sysentersyscallsysenterx86_64syscallLinux2.6sysenterint 80syscall/sysenter

Go 语言中的系统调用

amd64

// In syscall_unix.go
func Syscall(trap, a1, a2, a3 uintptr) (r1, r2 uintptr, err Errno)
func Syscall6(trap, a1, a2, a3, a4, a5, a6 uintptr) (r1, r2 uintptr, err Errno)
func RawSyscall(trap, a1, a2, a3 uintptr) (r1, r2 uintptr, err Errno)
func RawSyscall6(trap, a1, a2, a3, a4, a5, a6 uintptr) (r1, r2 uintptr, err Errno)

SyscallSyscall6amd64asm_linux_amd64.s

// func Syscall(trap int64, a1, a2, a3 uintptr) (r1, r2, err uintptr);
// Trap # in AX, args in DI SI DX R10 R8 R9, return in AX DX
// Note that this differs from "standard" ABI convention, which
// would pass 4th arg in CX, not R10.

TEXT ·Syscall(SB),NOSPLIT,$0-56
	CALL	runtime·entersyscall(SB)
	MOVQ	a1+8(FP), DI
	MOVQ	a2+16(FP), SI
	MOVQ	a3+24(FP), DX
	MOVQ	$0, R10
	MOVQ	$0, R8
	MOVQ	$0, R9
	MOVQ	trap+0(FP), AX	// syscall entry
	SYSCALL
	CMPQ	AX, $0xfffffffffffff001
	JLS	ok
	MOVQ	$-1, r1+32(FP)
	MOVQ	$0, r2+40(FP)
	NEGQ	AX
	MOVQ	AX, err+48(FP)
	CALL	runtime·exitsyscall(SB)
	RET
ok:
	MOVQ	AX, r1+32(FP)
	MOVQ	DX, r2+40(FP)
	MOVQ	$0, err+48(FP)
	CALL	runtime·exitsyscall(SB)
	RET

// func Syscall6(trap, a1, a2, a3, a4, a5, a6 uintptr) (r1, r2, err uintptr)
TEXT ·Syscall6(SB),NOSPLIT,$0-80
	CALL	runtime·entersyscall(SB)
	MOVQ	a1+8(FP), DI
	MOVQ	a2+16(FP), SI
	MOVQ	a3+24(FP), DX
	MOVQ	a4+32(FP), R10
	MOVQ	a5+40(FP), R8
	MOVQ	a6+48(FP), R9
	MOVQ	trap+0(FP), AX	// syscall entry
	SYSCALL
	CMPQ	AX, $0xfffffffffffff001
	JLS	ok6
	MOVQ	$-1, r1+56(FP)
	MOVQ	$0, r2+64(FP)
	NEGQ	AX
	MOVQ	AX, err+72(FP)
	CALL	runtime·exitsyscall(SB)
	RET
ok6:
	MOVQ	AX, r1+56(FP)
	MOVQ	DX, r2+64(FP)
	MOVQ	$0, err+72(FP)
	CALL	runtime·exitsyscall(SB)
	RET

// func RawSyscall(trap, a1, a2, a3 uintptr) (r1, r2, err uintptr)
TEXT ·RawSyscall(SB),NOSPLIT,$0-56
	MOVQ	a1+8(FP), DI
	MOVQ	a2+16(FP), SI
	MOVQ	a3+24(FP), DX
	MOVQ	$0, R10
	MOVQ	$0, R8
	MOVQ	$0, R9
	MOVQ	trap+0(FP), AX	// syscall entry
	SYSCALL
	CMPQ	AX, $0xfffffffffffff001
	JLS	ok1
	MOVQ	$-1, r1+32(FP)
	MOVQ	$0, r2+40(FP)
	NEGQ	AX
	MOVQ	AX, err+48(FP)
	RET
ok1:
	MOVQ	AX, r1+32(FP)
	MOVQ	DX, r2+40(FP)
	MOVQ	$0, err+48(FP)
	RET

// func RawSyscall6(trap, a1, a2, a3, a4, a5, a6 uintptr) (r1, r2, err uintptr)
TEXT ·RawSyscall6(SB),NOSPLIT,$0-80
	MOVQ	a1+8(FP), DI
	MOVQ	a2+16(FP), SI
	MOVQ	a3+24(FP), DX
	MOVQ	a4+32(FP), R10
	MOVQ	a5+40(FP), R8
	MOVQ	a6+48(FP), R9
	MOVQ	trap+0(FP), AX	// syscall entry
	SYSCALL
	CMPQ	AX, $0xfffffffffffff001
	JLS	ok2
	MOVQ	$-1, r1+56(FP)
	MOVQ	$0, r2+64(FP)
	NEGQ	AX
	MOVQ	AX, err+72(FP)
	RET
ok2:
	MOVQ	AX, r1+56(FP)
	MOVQ	DX, r2+64(FP)
	MOVQ	$0, err+72(FP)
	RET

SyscallRawSyscallruntimeSyscall

自己封装系统调用

PerlSyscall

package main

import (
    "fmt"
    "syscall"
)

func main() {
    pid, _, _ := syscall.Syscall(39, 0, 0, 0) // 用不到的就补上 0
    fmt.Println("Process id: ", pid)
}

输出如下：

name1e5s@asgard:~$ go run test.go 
Process id:  19184