github.com/twelsh-aw/go/src@v0.0.0-20230516233729-a56fe86a7c81/runtime/internal/syscall/asm_linux_amd64.s (about)

     1  // Copyright 2022 The Go Authors. All rights reserved.
     2  // Use of this source code is governed by a BSD-style
     3  // license that can be found in the LICENSE file.
     4  
     5  #include "textflag.h"
     6  
     7  // func Syscall6(num, a1, a2, a3, a4, a5, a6 uintptr) (r1, r2, errno uintptr)
     8  //
     9  // We need to convert to the syscall ABI.
    10  //
    11  // arg | ABIInternal | Syscall
    12  // ---------------------------
    13  // num | AX          | AX
    14  // a1  | BX          | DI
    15  // a2  | CX          | SI
    16  // a3  | DI          | DX
    17  // a4  | SI          | R10
    18  // a5  | R8          | R8
    19  // a6  | R9          | R9
    20  //
    21  // r1  | AX          | AX
    22  // r2  | BX          | DX
    23  // err | CX          | part of AX
    24  //
    25  // Note that this differs from "standard" ABI convention, which would pass 4th
    26  // arg in CX, not R10.
    27  TEXT ·Syscall6<ABIInternal>(SB),NOSPLIT,$0
    28  	// a6 already in R9.
    29  	// a5 already in R8.
    30  	MOVQ	SI, R10 // a4
    31  	MOVQ	DI, DX  // a3
    32  	MOVQ	CX, SI  // a2
    33  	MOVQ	BX, DI  // a1
    34  	// num already in AX.
    35  	SYSCALL
    36  	CMPQ	AX, $0xfffffffffffff001
    37  	JLS	ok
    38  	NEGQ	AX
    39  	MOVQ	AX, CX  // errno
    40  	MOVQ	$-1, AX // r1
    41  	MOVQ	$0, BX  // r2
    42  	RET
    43  ok:
    44  	// r1 already in AX.
    45  	MOVQ	DX, BX // r2
    46  	MOVQ	$0, CX // errno
    47  	RET