source: libcfa/src/concurrency/CtxSwitch-arm64.S@ 70f8bcd2

// 
// Cforall Version 1.0.0 Copyright (C) 2016 University of Waterloo
// 
// CtxSwitch-arm64.S -- 
// 
// Author           : Peter A. Buhr
// Created On       : Sun Aug 16 07:50:13 2020
// Last Modified By : Peter A. Buhr
// Last Modified On : Wed Aug 26 16:24:59 2020
// Update Count     : 25
// 

// The context switch routine requires the initial the stack of a thread to
// look like the thread has saved its context in the normal manner.

// Offsets must synchronized with the __stack_context_t in invoke.h.

#define PTR_BYTE        8
#define SP_OFFSET       ( 0 * PTR_BYTE )
#define FP_OFFSET       ( 1 * PTR_BYTE )

// Context switch between coroutines/tasks.
//   void __cfactx_switch( struct __stack_context_t * from, struct __stack_context_t * to ) ;
// Arguments "from" in register x0, "to" in register x1.

#define SAVE            20 * 8

        .file "CtxSwitch-arm64.S"
        .text
        .align 2
        .global __cfactx_switch
        .type __cfactx_switch, %function
__cfactx_switch:

        sub  sp, sp, #SAVE                                      // push stack

        // Save volatile GP registers x19-x30 on the stack.

        stp  x19, x20, [sp, #0x00]
        stp  x21, x22, [sp, #0x10]
        stp  x23, x24, [sp, #0x20]
        stp  x25, x26, [sp, #0x30]
        stp  x27, x28, [sp, #0x40]
        stp  x29, x30, [sp, #0x50]                      // x29 => fp

        // Save volatile SIMD/FPU registers d8-d15 on the stack.

        stp  d8,  d9,  [sp, #0x60]
        stp  d10, d11, [sp, #0x70]
        stp  d12, d13, [sp, #0x80]
        stp  d14, d15, [sp, #0x90]

        // Save old context in the "from" area.

        mov  x4, sp                                                     // cannot store sp directly
        str  x4, [x0, #SP_OFFSET]
        str  fp, [x0, #FP_OFFSET]

        // Load new context from the "to" area.

        ldr  fp, [x1, #FP_OFFSET]
        ldr  x4, [x1, #SP_OFFSET]
        mov  sp, x4                                                     // cannot store sp directly

        // Load volatile GP registers x19-x30 from the stack.

        ldp  x19, x20, [sp, #0x00]
        ldp  x21, x22, [sp, #0x10]
        ldp  x23, x24, [sp, #0x20]
        ldp  x25, x26, [sp, #0x30]
        ldp  x27, x28, [sp, #0x40]
        ldp  x29, x30, [sp, #0x50]
        
        // Load volatile SIMD/FPU registers d8-d15 from the stack.

        ldp  d8,  d9,  [sp, #0x60]
        ldp  d10, d11, [sp, #0x70]
        ldp  d12, d13, [sp, #0x80]
        ldp  d14, d15, [sp, #0x90]

        add  sp, sp, #SAVE                                      // pop stack
        ret                                                                     // return to new thread (mov pc, x30)

        .size __cfactx_switch, .-__cfactx_switch
        .section .note.GNU-stack,"",%progbits // mark no executable stack needed

// Stub to create new stacks which can be context switched to
//   void __cfactx_invoke_stub( void );

        .text
        .align 2
        .global __cfactx_invoke_stub
        .type __cfactx_invoke_stub, %function
__cfactx_invoke_stub:
        mov x0, x19                                                     // load main as parameter 0
        mov x1, x20                                                     // load this as parameter 1
        mov x30, x21                                            // load coroutine invoke routine
        ret                                                                     //   and jmp to it (mov pc, x30)
        .size __cfactx_invoke_stub, .-__cfactx_invoke_stub

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