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#============================================================================
# Keep a pointer to the main scheduler context.  This variable should be
# initialized to %rsp, which is done in the __sthread_start routine.
#
        .data
        .align 8
scheduler_context:      .quad   0


#============================================================================
# __sthread_switch is the main entry point for the thread scheduler.
# It has three parts:
#
#    1. Save the context of the current thread on the stack.
#       The context includes all of the integer registers and RFLAGS.
#
#    2. Call __sthread_scheduler (the C scheduler function), passing the
#       context as an argument.  The scheduler stack *must* be restored by
#       setting %rsp to the scheduler_context before __sthread_scheduler is
#       called.
#
#    3. __sthread_scheduler will return the context of a new thread.
#       Restore the context, and return to the thread.
#
        .text
        .align 8
        .globl __sthread_switch
__sthread_switch:

        # Save the process state onto its stack
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        pushq   %rax
        pushq   %rbx
        pushq   %rcx
        pushq   %rdx
        pushq   %rsi
        pushq   %rdi
        pushq   %rbp

        pushq   %r8
        pushq   %r9
        pushq   %r10
        pushq   %r11
        pushq   %r12
        pushq   %r13
        pushq   %r14
        pushq   %r15

        pushf
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        # Call the high-level scheduler with the current context as an argument
        movq    %rsp, %rdi
        movq    scheduler_context(%rip), %rsp
        call    __sthread_scheduler

        # The scheduler will return a context to start.
        # Restore the context to resume the thread.
__sthread_restore:
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        # returned context is new stack
        movq %rax, %rsp

        popf 

        popq   %r15
        popq   %r14
        popq   %r13
        popq   %r12
        popq   %r11
        popq   %r10
        popq   %r9
        popq   %r8

        popq   %rbp
        popq   %rdi
        popq   %rsi
        popq   %rdx
        popq   %rcx
        popq   %rbx
        popq   %rax
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        ret


#============================================================================
# Initialize a process context, given:
#    1. the stack for the process
#    2. the function to start
#    3. its argument
# The context should be consistent with that saved in the __sthread_switch
# routine.
#
# A pointer to the newly initialized context is returned to the caller.
# (This is the thread's stack-pointer after its context has been set up.)
#
# This function is described in more detail in sthread.c.
#
#
        .align 8
        .globl __sthread_initialize_context
__sthread_initialize_context:
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        # %rdi - stackp, %rsi - f, %rdx - arg
        # return value in %rax is the stack pointer,
        # leave 144 bytes for thread context details and return address.
        movq    %rdi, %rax
        subq    $144, %rax

        leaq    __sthread_finish(%rip), %rdi      
        movq    %rdi,  136(%rax)          # kill thread when done with f
        movq    %rsi,  128(%rax)          # address of f to come back to
        movq    $0,    120(%rax)          # rax = 0
        movq    $0,    112(%rax)          # rcx = 0
        movq    $0,    96(%rax)           # rdx = 0
        movq    $0,    88(%rax)           # rsi = 0
        movq    %rdx,  80(%rax)           # rdi = arg
        movq    $0,    72(%rax)           # rbp = 0
        movq    $0,    64(%rax)           # r9  = 0
        movq    $0,    48(%rax)           # r10 = 0
        movq    $0,    40(%rax)           # r11 = 0
        movq    $0,    32(%rax)           # r12 = 0
        movq    $0,    24(%rax)           # r13 = 0
        movq    $0,    16(%rax)           # r14 = 0
        movq    $0,    8(%rax)            # r15 = 0
        movq    $0,    (%rax)             # rflags = 0
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        ret


#============================================================================
# The start routine initializes the scheduler_context variable, and calls
# the __sthread_scheduler with a NULL context.
#
# The scheduler will return a context to resume.
#
        .align 8
        .globl __sthread_start
__sthread_start:
        # Remember the context
        movq    %rsp, scheduler_context(%rip)

        # Call the scheduler with no context
        movl    $0, %edi  # Also clears upper 4 bytes of %rdi
        call    __sthread_scheduler

        # Restore the context returned by the scheduler
        jmp     __sthread_restore