github.com/jwijenbergh/purego@v0.0.0-20240126093400-70ff3a61df13/internal/fakecgo/trampolines_amd64.s (about)

     1  // SPDX-License-Identifier: Apache-2.0
     2  // SPDX-FileCopyrightText: 2022 The Ebitengine Authors
     3  
     4  //go:build darwin || linux || freebsd
     5  
     6  /*
     7  trampoline for emulating required C functions for cgo in go (see cgo.go)
     8  (we convert cdecl calling convention to go and vice-versa)
     9  
    10  Since we're called from go and call into C we can cheat a bit with the calling conventions:
    11   - in go all the registers are caller saved
    12   - in C we have a couple of callee saved registers
    13  
    14  => we can use BX, R12, R13, R14, R15 instead of the stack
    15  
    16  C Calling convention cdecl used here (we only need integer args):
    17  1. arg: DI
    18  2. arg: SI
    19  3. arg: DX
    20  4. arg: CX
    21  5. arg: R8
    22  6. arg: R9
    23  We don't need floats with these functions -> AX=0
    24  return value will be in AX
    25  */
    26  #include "textflag.h"
    27  #include "go_asm.h"
    28  
    29  // these trampolines map the gcc ABI to Go ABI and then calls into the Go equivalent functions.
    30  
    31  TEXT x_cgo_init_trampoline(SB), NOSPLIT, $16
    32  	MOVQ DI, AX
    33  	MOVQ SI, BX
    34  	MOVQ ·x_cgo_init_call(SB), DX
    35  	MOVQ (DX), CX
    36  	CALL CX
    37  	RET
    38  
    39  TEXT x_cgo_thread_start_trampoline(SB), NOSPLIT, $8
    40  	MOVQ DI, AX
    41  	MOVQ ·x_cgo_thread_start_call(SB), DX
    42  	MOVQ (DX), CX
    43  	CALL CX
    44  	RET
    45  
    46  TEXT x_cgo_setenv_trampoline(SB), NOSPLIT, $8
    47  	MOVQ DI, AX
    48  	MOVQ ·x_cgo_setenv_call(SB), DX
    49  	MOVQ (DX), CX
    50  	CALL CX
    51  	RET
    52  
    53  TEXT x_cgo_unsetenv_trampoline(SB), NOSPLIT, $8
    54  	MOVQ DI, AX
    55  	MOVQ ·x_cgo_unsetenv_call(SB), DX
    56  	MOVQ (DX), CX
    57  	CALL CX
    58  	RET
    59  
    60  TEXT x_cgo_notify_runtime_init_done_trampoline(SB), NOSPLIT, $0
    61  	CALL ·x_cgo_notify_runtime_init_done(SB)
    62  	RET
    63  
    64  TEXT x_cgo_bindm_trampoline(SB), NOSPLIT, $0
    65  	CALL ·x_cgo_bindm(SB)
    66  	RET
    67  
    68  // func setg_trampoline(setg uintptr, g uintptr)
    69  TEXT ·setg_trampoline(SB), NOSPLIT, $0-16
    70  	MOVQ G+8(FP), DI
    71  	MOVQ setg+0(FP), BX
    72  	XORL AX, AX
    73  	CALL BX
    74  	RET
    75  
    76  TEXT threadentry_trampoline(SB), NOSPLIT, $16
    77  	MOVQ DI, AX
    78  	MOVQ ·threadentry_call(SB), DX
    79  	MOVQ (DX), CX
    80  	CALL CX
    81  	RET
    82  
    83  TEXT ·call5(SB), NOSPLIT, $0-56
    84  	MOVQ fn+0(FP), BX
    85  	MOVQ a1+8(FP), DI
    86  	MOVQ a2+16(FP), SI
    87  	MOVQ a3+24(FP), DX
    88  	MOVQ a4+32(FP), CX
    89  	MOVQ a5+40(FP), R8
    90  
    91  	XORL AX, AX // no floats
    92  
    93  	PUSHQ BP       // save BP
    94  	MOVQ  SP, BP   // save SP inside BP bc BP is callee-saved
    95  	SUBQ  $16, SP  // allocate space for alignment
    96  	ANDQ  $-16, SP // align on 16 bytes for SSE
    97  
    98  	CALL BX
    99  
   100  	MOVQ BP, SP // get SP back
   101  	POPQ BP     // restore BP
   102  
   103  	MOVQ AX, ret+48(FP)
   104  	RET