github.com/twelsh-aw/go/src@v0.0.0-20230516233729-a56fe86a7c81/runtime/time_linux_amd64.s (about)

     1  // Copyright 2021 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  //go:build !faketime
     6  
     7  #include "go_asm.h"
     8  #include "go_tls.h"
     9  #include "textflag.h"
    10  
    11  #define SYS_clock_gettime	228
    12  
    13  // func time.now() (sec int64, nsec int32, mono int64)
    14  TEXT time·now<ABIInternal>(SB),NOSPLIT,$16-24
    15  	MOVQ	SP, R12 // Save old SP; R12 unchanged by C code.
    16  
    17  	MOVQ	g_m(R14), BX // BX unchanged by C code.
    18  
    19  	// Set vdsoPC and vdsoSP for SIGPROF traceback.
    20  	// Save the old values on stack and restore them on exit,
    21  	// so this function is reentrant.
    22  	MOVQ	m_vdsoPC(BX), CX
    23  	MOVQ	m_vdsoSP(BX), DX
    24  	MOVQ	CX, 0(SP)
    25  	MOVQ	DX, 8(SP)
    26  
    27  	LEAQ	sec+0(FP), DX
    28  	MOVQ	-8(DX), CX	// Sets CX to function return address.
    29  	MOVQ	CX, m_vdsoPC(BX)
    30  	MOVQ	DX, m_vdsoSP(BX)
    31  
    32  	CMPQ	R14, m_curg(BX)	// Only switch if on curg.
    33  	JNE	noswitch
    34  
    35  	MOVQ	m_g0(BX), DX
    36  	MOVQ	(g_sched+gobuf_sp)(DX), SP	// Set SP to g0 stack
    37  
    38  noswitch:
    39  	SUBQ	$32, SP		// Space for two time results
    40  	ANDQ	$~15, SP	// Align for C code
    41  
    42  	MOVL	$0, DI // CLOCK_REALTIME
    43  	LEAQ	16(SP), SI
    44  	MOVQ	runtime·vdsoClockgettimeSym(SB), AX
    45  	CMPQ	AX, $0
    46  	JEQ	fallback
    47  	CALL	AX
    48  
    49  	MOVL	$1, DI // CLOCK_MONOTONIC
    50  	LEAQ	0(SP), SI
    51  	MOVQ	runtime·vdsoClockgettimeSym(SB), AX
    52  	CALL	AX
    53  
    54  ret:
    55  	MOVQ	16(SP), AX	// realtime sec
    56  	MOVQ	24(SP), DI	// realtime nsec (moved to BX below)
    57  	MOVQ	0(SP), CX	// monotonic sec
    58  	IMULQ	$1000000000, CX
    59  	MOVQ	8(SP), DX	// monotonic nsec
    60  
    61  	MOVQ	R12, SP		// Restore real SP
    62  
    63  	// Restore vdsoPC, vdsoSP
    64  	// We don't worry about being signaled between the two stores.
    65  	// If we are not in a signal handler, we'll restore vdsoSP to 0,
    66  	// and no one will care about vdsoPC. If we are in a signal handler,
    67  	// we cannot receive another signal.
    68  	MOVQ	8(SP), SI
    69  	MOVQ	SI, m_vdsoSP(BX)
    70  	MOVQ	0(SP), SI
    71  	MOVQ	SI, m_vdsoPC(BX)
    72  
    73  	// set result registers; AX is already correct
    74  	MOVQ	DI, BX
    75  	ADDQ	DX, CX
    76  	RET
    77  
    78  fallback:
    79  	MOVQ	$SYS_clock_gettime, AX
    80  	SYSCALL
    81  
    82  	MOVL	$1, DI // CLOCK_MONOTONIC
    83  	LEAQ	0(SP), SI
    84  	MOVQ	$SYS_clock_gettime, AX
    85  	SYSCALL
    86  
    87  	JMP	ret