.intel_syntax noprefix

// void context_switch(UINT64* old_rsp, UINT64 new_rsp)
// rdi = &old_rsp  (pointer to save current RSP)
// rsi = new_rsp   (value of new stack pointer)
//
// Saves/restores callee-saved registers only.
// On first switch into a new task, ret lands on task_entry_trampoline.
.global context_switch
context_switch:
    push rbx
    push rbp
    push r12
    push r13
    push r14
    push r15

    mov [rdi], rsp      // save current RSP
    mov rsp, rsi        // switch to new stack

    pop r15
    pop r14
    pop r13
    pop r12
    pop rbp
    pop rbx

    ret

.section .note.GNU-stack,"",@progbits