/*
 * Copyright 2019, Jérôme Duval, jerome.duval@gmail.com.
 * Copyright 2008, Ingo Weinhold, ingo_weinhold@gmx.de.
 * Distributed under the terms of the MIT License.
 */

#include <asm_defs.h>


call_stub:
        // push arguments on the stack
        push    %r9
        push    %r8
        push    %rcx
        push    %rdx
        push    %rsi
        push    %rdi
        // pointer to ourself
        lea             call_stub(%rip), %rdi
        // pointer to first argument
        mov             %rsp, %rsi

        // call the wrapper function
        movq    (call_stub_callback_address - call_stub)(%rdi), %rax
        call    *%rax
                                // returns a pointer to the actual function
        // restore arguments before calling
        pop             %rdi
        pop             %rsi
        pop             %rdx
        pop             %rcx
        pop             %r8
        pop             %r9
        jmp             *%rax

.align 8
call_stub_callback_address:
        .long   0
call_stub_end:


// size_t arch_call_stub_size();
FUNCTION(arch_call_stub_size):
        movq    $(call_stub_end - call_stub), %rax
        ret
FUNCTION_END(arch_call_stub_size)


// void arch_init_call_stub(void* stub,
//              void* (*callback)(const void* stub, const void* args),
//              void* function);
FUNCTION(arch_init_call_stub):
        push    %rbp
        movq    %rsp, %rbp

        push    %rsi
        push    %rdi

        // copy the stub
        movq    $(call_stub_end - call_stub), %rdx
        lea             call_stub(%rip), %rsi
        call    memcpy@plt

        // set the callback address in the stub
        pop             %rdi
        pop             %rsi
        movq    %rsi, (call_stub_callback_address - call_stub)(%rdi)

        movq    %rbp, %rsp
        pop             %rbp
        ret
FUNCTION_END(arch_init_call_stub)