ref: e281949b99fc3e5b9a9a49a7abaf95b36be88dde
dir: /libstd/syscall+plan9-x64.s/
.globl sys$syscall
sys$syscall:
/*
Ugly: Kernel is caller-save, Myrddin
is callee-save. We need to preserve
registers before entering the kernel.
However, we also need SP to point to the
start of the arguments.
Luckily, the kernel doesn't touch our stack,
and we have 256 bytes of gap if we get a note.
*/
MOVQ BX,-16(SP)
MOVQ CX,-24(SP)
MOVQ DX,-32(SP)
MOVQ SI,-40(SP)
MOVQ DI,-48(SP)
MOVQ BP,-56(SP)
MOVQ R8,-64(SP)
MOVQ R9,-72(SP)
MOVQ R10,-80(SP)
MOVQ R11,-88(SP)
MOVQ R12,-104(SP)
MOVQ R13,-112(SP)
MOVQ R14,-120(SP)
MOVQ R15,-128(SP)
ADDQ $8,SP
SYSCALL
SUBQ $8,SP
MOVQ -16(SP),BX
MOVQ -24(SP),CX
MOVQ -32(SP),DX
MOVQ -40(SP),SI
MOVQ -48(SP),DI
MOVQ -56(SP),BP
MOVQ -64(SP),R8
MOVQ -72(SP),R9
MOVQ -80(SP),R10
MOVQ -88(SP),R11
MOVQ -104(SP),R12
MOVQ -112(SP),R13
MOVQ -120(SP),R14
MOVQ -128(SP),R15
RET