/**
 * Support code for mutithreading.
 *
 * Copyright: Copyright Mikola Lysenko 2005 - 2012.
 * License:   $(WEB www.boost.org/LICENSE_1_0.txt, Boost License 1.0).
 * Authors:   Mikola Lysenko, Martin Nowak, Kai Nacke
 */

/*
 *          Copyright Mikola Lysenko 2005 - 2012.
 * Distributed under the Boost Software License, Version 1.0.
 *    (See accompanying file LICENSE_1_0.txt or copy at
 *          http://www.boost.org/LICENSE_1_0.txt)
 */

#if (defined(__linux__) || defined(__FreeBSD__) || defined(__NetBSD__)) && defined(__ELF__)
/*
 * Mark the resulting object file as not requiring execution permissions on
 * stack memory. The absence of this section would mark the whole resulting
 * library as requiring an executable stack, making it impossible to
 * dynamically load druntime on several Linux platforms where this is
 * forbidden due to security policies.
 */
.section .note.GNU-stack,"",%progbits
#endif

/* Let preprocessor tell us if C symbols have a prefix: __USER_LABEL_PREFIX__ */
#ifdef __USER_LABEL_PREFIX__
#define GLUE2(a, b) a ## b
#define GLUE(a, b) GLUE2(a, b)
#define CSYM(name) GLUE(__USER_LABEL_PREFIX__, name)
#else
#define CSYM(name) name
#endif

/************************************************************************************
 * POWER PC ASM BITS
 ************************************************************************************/
#if defined( __PPC64__ )

/**
 * Performs a context switch.
 * r3: location where to store current stack pointer
 * r4: new stack pointer
 *
 * The stack frame uses the standard layout except for floating point and
 * vector registers.
 *
 * ELFv2:
 * +------------------------+
 * | TOC Pointer Doubleword | SP+24
 * +------------------------+
 * | LR Save Doubleword     | SP+16
 * +------------------------+
 * | Reserved               | SP+12
 * +------------------------+
 * | CR Save Word           | SP+8
 * +------------------------+
 * | Back Chain             | SP+176 <-- Previous function
 * +------------------------+
 * | GPR Save Area (14-31)  | SP+32
 * +------------------------+
 * | TOC Pointer Doubleword | SP+24
 * +------------------------+
 * | LR Save Doubleword     | SP+16
 * +------------------------+
 * | Reserved               | SP+12
 * +------------------------+
 * | CR Save Word           | SP+8
 * +------------------------+
 * | Back Chain             | SP+0   <-- Stored stack pointer
 * +------------------------+
 * | VR Save Area (20-31)   | SP-16
 * +------------------------+
 * | FPR Save Area (14-31)  | SP-200
 * +------------------------+
 *
 * ELFv1:
 * +------------------------+
 * | Parameter Save Area    | SP+48
 * +------------------------+
 * | TOC Pointer Doubleword | SP+40
 * +------------------------+
 * | Link editor doubleword | SP+32
 * +------------------------+
 * | Compiler Doubleword    | SP+24
 * +------------------------+
 * | LR Save Doubleword     | SP+16
 * +------------------------+
 * | Reserved               | SP+12
 * +------------------------+
 * | CR Save Word           | SP+8
 * +------------------------+
 * | Back Chain             | SP+256 <-- Previous function
 * +------------------------+
 * | GPR Save Area (14-31)  | SP+112
 * +------------------------+
 * | Parameter Save Area    | SP+48
 * +------------------------+
 * | TOC Pointer Doubleword | SP+40
 * +------------------------+
 * | Link editor doubleword | SP+32
 * +------------------------+
 * | Compiler Doubleword    | SP+24
 * +------------------------+
 * | LR Save Doubleword     | SP+16
 * +------------------------+
 * | Reserved               | SP+12
 * +------------------------+
 * | CR Save Word           | SP+8
 * +------------------------+
 * | Back Chain             | SP+0   <-- Stored stack pointer
 * +------------------------+
 * | VR Save Area (20-31)   | SP-16
 * +------------------------+
 * | FPR Save Area (14-31)  | SP-200
 * +------------------------+
 */

#if defined(_CALL_ELF) && _CALL_ELF == 2
#define USE_ABI_2
#define LINKAGE_SZ   32
#define CR_OFS       8
#define LR_OFS       16
#define TOC_OFS      24
#define GPR_OFS      32
#define STACK_SZ     (LINKAGE_SZ + 18*8)
#else
#define LINKAGE_SZ   48
#define CR_OFS       8
#define LR_OFS       16
#define TOC_OFS      40
#define GPR_OFS      112
#define STACK_SZ     (LINKAGE_SZ + 8*8 + 18*8)
#endif

    .text
#if defined( USE_ABI_2 )
    .abiversion 2
#endif
    .align 2
    .globl fiber_switchContext
    .type  fiber_switchContext,@function
#if defined( USE_ABI_2 )
    .section .text.fiber_switchContext,"a",@progbits
#else
    .section .opd,"aw",@progbits
#endif
fiber_switchContext:
#if !defined( USE_ABI_2 )
    .align  3
    .quad .L.fiber_switchContext
    .quad .TOC.@tocbase
    .quad 0
    .text
#endif
.L.fiber_switchContext:
    .cfi_startproc
#if defined( USE_ABI_2 )
    addis 2, 12, .TOC.-.L.fiber_switchContext@ha
    addi 2, 2, .TOC.-.L.fiber_switchContext@l
    .localentry fiber_switchContext, .-.L.fiber_switchContext
#endif
    mflr    0
    std     0, LR_OFS(1)
    stdu    1, -STACK_SZ(1)
    .cfi_def_cfa_offset STACK_SZ
    .cfi_offset lr, LR_OFS

    /* Update the old stack pointer */
    std     1, 0(3)

    /* Save CC and TOC */
    mfcr    0
    sth     0,  CR_OFS(1)
    std     2,  TOC_OFS(1)

    /* Save GPRs */
    std     14, (GPR_OFS +  0 * 8)(1)
    std     15, (GPR_OFS +  1 * 8)(1)
    std     16, (GPR_OFS +  2 * 8)(1)
    std     17, (GPR_OFS +  3 * 8)(1)
    std     18, (GPR_OFS +  4 * 8)(1)
    std     19, (GPR_OFS +  5 * 8)(1)
    std     20, (GPR_OFS +  6 * 8)(1)
    std     21, (GPR_OFS +  7 * 8)(1)
    std     22, (GPR_OFS +  8 * 8)(1)
    std     23, (GPR_OFS +  9 * 8)(1)
    std     24, (GPR_OFS + 10 * 8)(1)
    std     25, (GPR_OFS + 11 * 8)(1)
    std     26, (GPR_OFS + 12 * 8)(1)
    std     27, (GPR_OFS + 13 * 8)(1)
    std     28, (GPR_OFS + 14 * 8)(1)
    std     29, (GPR_OFS + 15 * 8)(1)
    std     30, (GPR_OFS + 16 * 8)(1)
    std     31, (GPR_OFS + 17 * 8)(1)

    /* Save VRs */
    addi    0, 1, (- 1 * 16)
    stvx    20, 0, 0
    addi    0, 1, (- 2 * 16)
    stvx    21, 0, 0
    addi    0, 1, (- 3 * 16)
    stvx    22, 0, 0
    addi    0, 1, (- 4 * 16)
    stvx    23, 0, 0
    addi    0, 1, (- 5 * 16)
    stvx    24, 0, 0
    addi    0, 1, (- 6 * 16)
    stvx    25, 0, 0
    addi    0, 1, (- 7 * 16)
    stvx    26, 0, 0
    addi    0, 1, (- 8 * 16)
    stvx    27, 0, 0
    addi    0, 1, (- 9 * 16)
    stvx    28, 0, 0
    addi    0, 1, (-10 * 16)
    stvx    29, 0, 0
    addi    0, 1, (-11 * 16)
    stvx    30, 0, 0
    addi    0, 1, (-12 * 16)
    stvx    31, 0, 0

    /* Save FPRs */
    stfd    14, ( -1 * 8 -12 * 16)(1)
    stfd    15, ( -2 * 8 -12 * 16)(1)
    stfd    16, ( -3 * 8 -12 * 16)(1)
    stfd    17, ( -4 * 8 -12 * 16)(1)
    stfd    18, ( -5 * 8 -12 * 16)(1)
    stfd    19, ( -6 * 8 -12 * 16)(1)
    stfd    20, ( -7 * 8 -12 * 16)(1)
    stfd    21, ( -8 * 8 -12 * 16)(1)
    stfd    22, ( -9 * 8 -12 * 16)(1)
    stfd    23, (-10 * 8 -12 * 16)(1)
    stfd    24, (-11 * 8 -12 * 16)(1)
    stfd    25, (-12 * 8 -12 * 16)(1)
    stfd    26, (-13 * 8 -12 * 16)(1)
    stfd    27, (-14 * 8 -12 * 16)(1)
    stfd    28, (-15 * 8 -12 * 16)(1)
    stfd    29, (-16 * 8 -12 * 16)(1)
    stfd    30, (-17 * 8 -12 * 16)(1)
    stfd    31, (-18 * 8 -12 * 16)(1)

    /* Set new stack pointer */
    mr      1, 4

    /* Restore GPRs */
    ld     14, (GPR_OFS +  0 * 8)(1)
    ld     15, (GPR_OFS +  1 * 8)(1)
    ld     16, (GPR_OFS +  2 * 8)(1)
    ld     17, (GPR_OFS +  3 * 8)(1)
    ld     18, (GPR_OFS +  4 * 8)(1)
    ld     19, (GPR_OFS +  5 * 8)(1)
    ld     20, (GPR_OFS +  6 * 8)(1)
    ld     21, (GPR_OFS +  7 * 8)(1)
    ld     22, (GPR_OFS +  8 * 8)(1)
    ld     23, (GPR_OFS +  9 * 8)(1)
    ld     24, (GPR_OFS + 10 * 8)(1)
    ld     25, (GPR_OFS + 11 * 8)(1)
    ld     26, (GPR_OFS + 12 * 8)(1)
    ld     27, (GPR_OFS + 13 * 8)(1)
    ld     28, (GPR_OFS + 14 * 8)(1)
    ld     29, (GPR_OFS + 15 * 8)(1)
    ld     30, (GPR_OFS + 16 * 8)(1)
    ld     31, (GPR_OFS + 17 * 8)(1)

    /* Load VRs */
    addi    0, 1, (- 1 * 16)
    lvx     20, 0, 0
    addi    0, 1, (- 2 * 16)
    lvx     21, 0, 0
    addi    0, 1, (- 3 * 16)
    lvx     22, 0, 0
    addi    0, 1, (- 4 * 16)
    lvx     23, 0, 0
    addi    0, 1, (- 5 * 16)
    lvx     24, 0, 0
    addi    0, 1, (- 6 * 16)
    lvx     25, 0, 0
    addi    0, 1, (- 7 * 16)
    lvx     26, 0, 0
    addi    0, 1, (- 8 * 16)
    lvx     27, 0, 0
    addi    0, 1, (- 9 * 16)
    lvx     28, 0, 0
    addi    0, 1, (-10 * 16)
    lvx     29, 0, 0
    addi    0, 1, (-11 * 16)
    lvx     30, 0, 0
    addi    0, 1, (-12 * 16)
    lvx     31, 0, 0

    /* Restore FPRs */
    lfd     14, ( -1 * 8 -12 * 16)(1)
    lfd     15, ( -2 * 8 -12 * 16)(1)
    lfd     16, ( -3 * 8 -12 * 16)(1)
    lfd     17, ( -4 * 8 -12 * 16)(1)
    lfd     18, ( -5 * 8 -12 * 16)(1)
    lfd     19, ( -6 * 8 -12 * 16)(1)
    lfd     20, ( -7 * 8 -12 * 16)(1)
    lfd     21, ( -8 * 8 -12 * 16)(1)
    lfd     22, ( -9 * 8 -12 * 16)(1)
    lfd     23, (-10 * 8 -12 * 16)(1)
    lfd     24, (-11 * 8 -12 * 16)(1)
    lfd     25, (-12 * 8 -12 * 16)(1)
    lfd     26, (-13 * 8 -12 * 16)(1)
    lfd     27, (-14 * 8 -12 * 16)(1)
    lfd     28, (-15 * 8 -12 * 16)(1)
    lfd     29, (-16 * 8 -12 * 16)(1)
    lfd     30, (-17 * 8 -12 * 16)(1)
    lfd     31, (-18 * 8 -12 * 16)(1)

    /* Set condition and TOC register */
    lhz     0, CR_OFS(1)
    mtcr    0
    ld      2, TOC_OFS(1)

    /* Return and switch context */
    addi    1, 1, STACK_SZ
    ld      0, LR_OFS(1)
    mtlr    0
    blr
    .long 0
    .quad 0
    .size  fiber_switchContext,.-.L.fiber_switchContext
    .cfi_endproc

#elif defined( __ppc__ ) || defined( __PPC__ ) || defined( __powerpc__ )

    .section  ".text"

/**
 * Performs a context switch.
 *
 * r3 - old context pointer
 * r4 - new context pointer
 *
 */
    .align 2
    .globl fiber_switchContext
    .type   fiber_switchContext, @function
fiber_switchContext:
    /* Save linkage area */
    mflr        0
    mfcr        5
    stw     0, 8(1)
    stw     5, 4(1)

    /* Save GPRs */
    stw     11, (-1 * 4)(1)
    stw     13, (-2 * 4)(1)
    stw     14, (-3 * 4)(1)
    stw     15, (-4 * 4)(1)
    stw     16, (-5 * 4)(1)
    stw     17, (-6 * 4)(1)
    stw     18, (-7 * 4)(1)
    stw     19, (-8 * 4)(1)
    stw     20, (-9 * 4)(1)
    stw     21, (-10 * 4)(1)
    stw     22, (-11 * 4)(1)
    stw     23, (-12 * 4)(1)
    stw     24, (-13 * 4)(1)
    stw     25, (-14 * 4)(1)
    stw     26, (-15 * 4)(1)
    stw     27, (-16 * 4)(1)
    stw     28, (-17 * 4)(1)
    stw     29, (-18 * 4)(1)
    stw     30, (-19 * 4)(1)
    stwu    31, (-20 * 4)(1)

    /* We update the stack pointer here, since we do not want the GC to
       scan the floating point registers. */

    /* Save FPRs */
    stfd    14, (-1 * 8)(1)
    stfd    15, (-2 * 8)(1)
    stfd    16, (-3 * 8)(1)
    stfd    17, (-4 * 8)(1)
    stfd    18, (-5 * 8)(1)
    stfd    19, (-6 * 8)(1)
    stfd    20, (-7 * 8)(1)
    stfd    21, (-8 * 8)(1)
    stfd    22, (-9 * 8)(1)
    stfd    23, (-10 * 8)(1)
    stfd    24, (-11 * 8)(1)
    stfd    25, (-12 * 8)(1)
    stfd    26, (-13 * 8)(1)
    stfd    27, (-14 * 8)(1)
    stfd    28, (-15 * 8)(1)
    stfd    29, (-16 * 8)(1)
    stfd    30, (-17 * 8)(1)
    stfd    31, (-18 * 8)(1)

    /* Update the old stack pointer */
    stw     1, 0(3)

    /* Set new stack pointer */
    addi        1, 4, 20 * 4

    /* Restore linkage area */
    lwz     0, 8(1)
    lwz     5, 4(1)

    /* Restore GPRs */
    lwz     11, (-1 * 4)(1)
    lwz     13, (-2 * 4)(1)
    lwz     14, (-3 * 4)(1)
    lwz     15, (-4 * 4)(1)
    lwz     16, (-5 * 4)(1)
    lwz     17, (-6 * 4)(1)
    lwz     18, (-7 * 4)(1)
    lwz     19, (-8 * 4)(1)
    lwz     20, (-9 * 4)(1)
    lwz     21, (-10 * 4)(1)
    lwz     22, (-11 * 4)(1)
    lwz     23, (-12 * 4)(1)
    lwz     24, (-13 * 4)(1)
    lwz     25, (-14 * 4)(1)
    lwz     26, (-15 * 4)(1)
    lwz     27, (-16 * 4)(1)
    lwz     28, (-17 * 4)(1)
    lwz     29, (-18 * 4)(1)
    lwz     30, (-19 * 4)(1)
    lwz     31, (-20 * 4)(1)


    /* Restore FPRs */
    lfd     14, (-1 * 8)(4)
    lfd     15, (-2 * 8)(4)
    lfd     16, (-3 * 8)(4)
    lfd     17, (-4 * 8)(4)
    lfd     18, (-5 * 8)(4)
    lfd     19, (-6 * 8)(4)
    lfd     20, (-7 * 8)(4)
    lfd     21, (-8 * 8)(4)
    lfd     22, (-9 * 8)(4)
    lfd     23, (-10 * 8)(4)
    lfd     24, (-11 * 8)(4)
    lfd     25, (-12 * 8)(4)
    lfd     26, (-13 * 8)(4)
    lfd     27, (-14 * 8)(4)
    lfd     28, (-15 * 8)(4)
    lfd     29, (-16 * 8)(4)
    lfd     30, (-17 * 8)(4)
    lfd     31, (-18 * 8)(4)

    /* Set condition and link register */
    mtcr        5
    mtlr        0

    /* Return and switch context */
    blr
    .size  fiber_switchContext,.-fiber_switchContext

#elif defined(__mips__) && _MIPS_SIM == _ABIO32
/************************************************************************************
 * MIPS ASM BITS
 ************************************************************************************/

/**
 * Performs a context switch.
 *
 * $a0 - void** - ptr to old stack pointer
 * $a1 - void*  - new stack pointer
 *
 */
.text
.globl fiber_switchContext
fiber_switchContext:
    addiu $sp, $sp, -(10 * 4)

    // fp regs and return address are stored below the stack
    // because we don't want the GC to scan them.

#ifdef __mips_hard_float
#define ALIGN8(val) (val + (-val & 7))
#define BELOW (ALIGN8(6 * 8 + 4))
    sdcl $f20, (0 * 8 - BELOW)($sp)
    sdcl $f22, (1 * 8 - BELOW)($sp)
    sdcl $f24, (2 * 8 - BELOW)($sp)
    sdcl $f26, (3 * 8 - BELOW)($sp)
    sdcl $f28, (4 * 8 - BELOW)($sp)
    sdcl $f30, (5 * 8 - BELOW)($sp)
#endif
    sw $ra, -4($sp)

    sw $s0, (0 * 4)($sp)
    sw $s1, (1 * 4)($sp)
    sw $s2, (2 * 4)($sp)
    sw $s3, (3 * 4)($sp)
    sw $s4, (4 * 4)($sp)
    sw $s5, (5 * 4)($sp)
    sw $s6, (6 * 4)($sp)
    sw $s7, (7 * 4)($sp)
    sw $s8, (8 * 4)($sp)
    sw $gp, (9 * 4)($sp)

    // swap stack pointer
    sw $sp, 0($a0)
    move $sp, $a1

#ifdef __mips_hard_float
    ldcl $f20, (0 * 8 - BELOW)($sp)
    ldcl $f22, (1 * 8 - BELOW)($sp)
    ldcl $f24, (2 * 8 - BELOW)($sp)
    ldcl $f26, (3 * 8 - BELOW)($sp)
    ldcl $f28, (4 * 8 - BELOW)($sp)
    ldcl $f30, (5 * 8 - BELOW)($sp)
#endif
    lw $ra, -4($sp)

    lw $s0, (0 * 4)($sp)
    lw $s1, (1 * 4)($sp)
    lw $s2, (2 * 4)($sp)
    lw $s3, (3 * 4)($sp)
    lw $s4, (4 * 4)($sp)
    lw $s5, (5 * 4)($sp)
    lw $s6, (6 * 4)($sp)
    lw $s7, (7 * 4)($sp)
    lw $s8, (8 * 4)($sp)
    lw $gp, (9 * 4)($sp)

    addiu $sp, $sp, (10 * 4)

    jr $ra // return

#elif defined(__arm__) && defined(__ARM_EABI__)
/************************************************************************************
 * ARM ASM BITS
 ************************************************************************************/

/**
 * Performs a context switch.
 *
 * Parameters:
 * r0 - void** - ptr to old stack pointer
 * r1 - void*  - new stack pointer
 *
 * ARM EABI registers:
 * r0-r3   : argument/scratch registers
 * r4-r10  : callee-save registers
 * r11     : frame pointer (or a callee save register if fp isn't needed)
 * r12 =ip : inter procedure register. We can treat it like any other scratch register
 * r13 =sp : stack pointer
 * r14 =lr : link register, it contains the return address (belonging to the function which called us)
 * r15 =pc : program counter
 *
 * For floating point registers:
 * According to AAPCS (version 2.09, section 5.1.2) only the d8-d15 registers need to be preserved
 * across method calls. This applies to all ARM FPU variants, whether they have 16 or 32 double registers
 * NEON support or not, half-float support or not and so on does not matter.
 *
 * Note: If this file was compiled with -mfloat-abi=soft but the code runs on a softfp system with fpu the d8-d15
 * registers won't be saved (we do not know that the system has got a fpu in that case) but the registers might actually
 * be used by other code if it was compiled with -mfloat-abi=softfp.
 *
 * Interworking is only supported on ARMv5+, not on ARM v4T as ARM v4t requires special stubs when changing
 * from thumb to arm mode or the other way round.
 */

.text
.align  2
.global fiber_switchContext
#if defined(__ARM_PCS_VFP) || (defined(__ARM_PCS) && !defined(__SOFTFP__)) // ARM_HardFloat  || ARM_SoftFP
  .fpu vfp
#endif
.type   fiber_switchContext, %function
fiber_switchContext:
    .fnstart
    push {r4-r11}
    // update the oldp pointer. Link register and floating point registers stored later to prevent the GC from
    // scanning them.
    str sp, [r0]
    // push r0 (or any other register) as well to keep stack 8byte aligned
    push {r0, lr}

    #if defined(__ARM_PCS_VFP) || (defined(__ARM_PCS) && !defined(__SOFTFP__)) // ARM_HardFloat  || ARM_SoftFP
      vpush {d8-d15}
      // now switch over to the new stack. Need to subtract (8*8[d8-d15]+2*4[r0, lr]) to position stack pointer
      // below the last saved register. Remember we saved the SP before pushing [r0, lr, d8-d15]
      sub sp, r1, #72
      vpop {d8-d15}
    #else
      sub sp, r1, #8
    #endif

    // we don't really care about r0, we only used that for padding.
    // r1 is now what used to be in the link register when saving.
    pop {r0, r1, r4-r11}
    /**
     * The link register for the initial jump to fiber_entryPoint must be zero: The jump actually
     * looks like a normal method call as we jump to the start of the fiber_entryPoint function.
     * Although fiber_entryPoint never returns and therefore never accesses lr, it saves lr to the stack.
     * ARM unwinding will then look at the stack, find lr and think that fiber_entryPoint was called by
     * the function in lr! So if we have some address in lr the unwinder will try to continue stack unwinding,
     * although it's already at the stack base and crash.
     * In all other cases the content of lr doesn't matter.
     * Note: If we simply loaded into lr above and then moved lr into pc, the initial method call
     * to fiber_entryPoint would look as if it was called from fiber_entryPoint itself, as the fiber_entryPoint
     * address is in lr on the initial context switch.
     */
    mov lr, #0
    // return by writing lr into pc
    mov pc, r1
    .fnend

#elif defined(__aarch64__)
/************************************************************************************
 * AArch64 (arm64) ASM BITS
 ************************************************************************************/
/**
 * preserve/restore AAPCS64 registers
 *   x19-x28 5.1.1 64-bit callee saved
 *   x29 fp, or possibly callee saved reg - depends on platform choice 5.2.3)
 *   x30 lr
 *   d8-d15  5.1.2 says callee only must save bottom 64-bits (the "d" regs)
 *
 * saved regs on stack will look like:
 *   19: x19
 *   18: x20
 *   ...
 *   10: x28
 *    9: x29 (fp)  <-- oldp / *newp save stack top
 *    8: x30 (lr)
 *    7: d8
 *   ...
 *    0: d15       <-- sp
 */
        .text
        .global CSYM(fiber_switchContext)
        .p2align  2
CSYM(fiber_switchContext):
        stp     d15, d14, [sp, #-20*8]!
        stp     d13, d12, [sp, #2*8]
        stp     d11, d10, [sp, #4*8]
        stp     d9, d8,   [sp, #6*8]
        stp     x30, x29, [sp, #8*8] // lr, fp
        stp     x28, x27, [sp, #10*8]
        stp     x26, x25, [sp, #12*8]
        stp     x24, x23, [sp, #14*8]
        stp     x22, x21, [sp, #16*8]
        stp     x20, x19, [sp, #18*8]

        // oldp is set above saved lr (x30) to hide it and float regs
        // from GC
        add     x19, sp, #9*8
        str     x19, [x0]       // *oldp tstack
        sub     sp, x1, #9*8    // switch to newp sp

        ldp     x20, x19, [sp, #18*8]
        ldp     x22, x21, [sp, #16*8]
        ldp     x24, x23, [sp, #14*8]
        ldp     x26, x25, [sp, #12*8]
        ldp     x28, x27, [sp, #10*8]
        ldp     x30, x29, [sp, #8*8] // lr, fp
        ldp     d9, d8,   [sp, #6*8]
        ldp     d11, d10, [sp, #4*8]
        ldp     d13, d12, [sp, #2*8]
        ldp     d15, d14, [sp], #20*8
        ret
#endif
