github.com/notti/nocgo@v0.0.0-20190619201224-fc443047424c/internal/fakecgo/trampoline_amd64.s (about)

     1  /*
     2      trampoline for emulating required C functions for cgo in go (see cgo.go)
     3      (we convert cdecl calling convention to go and vice-versa)
     4  
     5      Since we're called from go and call into C we can cheat a bit with the calling conventions:
     6       - in go all the registers are caller saved
     7       - in C we have a couple of callee saved registers
     8  
     9      => we can use BX, R12, R13, R14, R15 instead of the stack
    10  
    11      C Calling convention cdecl used here (we only need integer args):
    12      1. arg: DI
    13      2. arg: SI
    14      3. arg: DX
    15      4. arg: CX
    16      5. arg: R8
    17      6. arg: R9
    18      We don't need floats with these functions -> AX=0
    19      return value will be in AX
    20  */
    21  #include "textflag.h"
    22  
    23  TEXT x_cgo_init_trampoline(SB),NOSPLIT,$16
    24      MOVQ DI, 0(SP)
    25      MOVQ SI, 8(SP)
    26      CALL ·x_cgo_init(SB)
    27      RET
    28  
    29  TEXT x_cgo_thread_start_trampoline(SB),NOSPLIT,$8
    30      MOVQ DI, 0(SP)
    31      CALL ·x_cgo_thread_start(SB)
    32      RET
    33  
    34  TEXT ·threadentry_trampoline(SB),NOSPLIT,$16
    35      MOVQ DI, 0(SP)
    36      CALL ·threadentry(SB)
    37      MOVQ 8(SP), AX
    38      RET
    39  
    40  // func setg_trampoline(setg uintptr, g uintptr)
    41  TEXT ·setg_trampoline(SB),NOSPLIT,$0-16
    42      MOVQ g+8(FP), DI
    43      MOVQ setg+0(FP), AX
    44      CALL AX
    45      RET
    46  
    47  TEXT x_cgo_notify_runtime_init_done_trampoline(SB),NOSPLIT,$0
    48      CALL ·x_cgo_notify_runtime_init_done(SB)
    49      RET
    50  
    51  TEXT x_cgo_setenv_trampoline(SB),NOSPLIT,$8
    52      MOVQ DI, 0(SP)
    53      CALL ·x_cgo_setenv(SB)
    54      RET
    55  
    56  TEXT x_cgo_unsetenv_trampoline(SB),NOSPLIT,$8
    57      MOVQ DI, 0(SP)
    58      CALL ·x_cgo_unsetenv(SB)
    59      RET
    60  
    61  // func asmlibccall6(fn, n, args uintptr) uintptr
    62  TEXT ·asmlibccall6(SB),NOSPLIT,$0-32
    63      MOVQ n+8(FP), AX
    64  
    65      TESTQ AX, AX
    66      JZ skipargs
    67  
    68      MOVQ args+16(FP), AX
    69      MOVQ 0(AX), DI
    70      MOVQ 8(AX), SI
    71      MOVQ 16(AX), DX
    72      MOVQ 24(AX), CX
    73      MOVQ 32(AX), R8
    74      MOVQ 40(AX), R9
    75  
    76  skipargs:
    77  
    78      MOVQ fn+0(FP), BX
    79  
    80      MOVQ SP, R12
    81      ANDQ $~0xF, SP // 16 byte alignment for cdecl
    82  
    83      XORQ AX, AX // no fp arguments
    84      CALL BX
    85  
    86      MOVQ R12, SP
    87  
    88      MOVQ AX, ret+24(FP)
    89  
    90      RET