source: bootcd/isolinux/syslinux-6.03/com32/lib/x86_64/setjmp.S

#
# arch/x86_64/setjmp.S
#
# setjmp/longjmp for the x86-64 architecture
#

#
# The jmp_buf is assumed to contain the following, in order:
#       %rbx
#       %rsp (post-return)
#       %rbp
#       %r12
#       %r13
#       %r14
#       %r15
#       <return address>
#

        .text
        .align 4
        .globl setjmp
        .type setjmp, @function
setjmp:
        pop  %rsi                       # Return address, and adjust the stack
        xorl %eax,%eax                  # Return value
        movq %rbx,(%rdi)
        movq %rsp,8(%rdi)               # Post-return %rsp!
        push %rsi                       # Make the call/return stack happy
        movq %rbp,16(%rdi)
        movq %r12,24(%rdi)
        movq %r13,32(%rdi)
        movq %r14,40(%rdi)
        movq %r15,48(%rdi)
        movq %rsi,56(%rdi)              # Return address
        ret

        .size setjmp,.-setjmp

        .text
        .align 4
        .globl longjmp
        .type longjmp, @function
longjmp:
        movl %esi,%eax                  # Return value (int)
        movq (%rdi),%rbx
        movq 8(%rdi),%rsp
        movq 16(%rdi),%rbp
        movq 24(%rdi),%r12
        movq 32(%rdi),%r13
        movq 40(%rdi),%r14
        movq 48(%rdi),%r15
        jmp *56(%rdi)

        .size longjmp,.-longjmp