ref: ba9f79ecd79a5d24b74f714cc8c70204d5bc26c5
dir: /libstd/syscall+plan9-x64.s/
/*
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.
*/
TEXT sys$syscall+0(SB),1,$0
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