c - 如何从汇编代码中调用 C 函数 printf 获取整数

Question

我在从汇编代码调用 printf 时遇到问题。我的函数 end_power 旨在打印 power 的结果，但每当我调用 printf 时，我都会遇到段错误。 (我在 64 位 Linux 上运行该程序)唯一不工作的部分是 end_power 函数，更具体地说是调用 printf 所涉及的行

# PURPOSE: This function is used to compute
#       the value of a number raised to
#       a power.
#
# INPUT:   First argument - the base number
#       Second argument - the power to
#       raise it to
#
# OUTPUT:  Will give the result as a return value
#
# NOTES:   The power must be 1 or greater
#
# VARIABLES:
#
#       %rbx - holds the base number
#       %rcx - holds the power
#
#       -8(%rbp) - holds the current result
#
#       %rax is used for temporary storage
#

.type power, @function
power:

    pushq   %rbp              # save old base pointer
    movq    %rsp, %rbp        # make stack pointer the base pointer
    subq    $8, %rsp          # get room for our local storage

    movq    16(%rbp), %rbx    # put first argument in %rax
    movq    24(%rbp), %rcx    # put second argument in %rcx

    movq    %rbx, -8(%rbp)    # store current result

power_loop_start:

    cmpq    $1, %rcx          # if the power is 1, we are done
    je      end_power

    movq    -8(%rbp), %rax    # move the current result into %rax
    imulq   %rbx, %rax        # multiply the current result by
                          # the base number
    movq    %rax, -8(%rbp)    # store the current result
    decq    %rcx              # decrease the power
    jmp     power_loop_start    # run for the next power

end_power:

    movq    -8(%rbp), %rdi    # return value goes in %rdi

    pushq -8(%rbp)
    pushq $fmtdec
    call printf
    add $16, %rsp

    movq    %rbp, %rsp        # restore the stack pointer
    popq    %rbp              # restore the base pointer
    ret

Answer 1

64 位 Linux 的调用约定与 32 位 Linux 的调用约定有很大不同。看看:http://en.wikipedia.org/wiki/X86_calling_conventions#System_V_AMD64_ABI

改变

pushq -8(%rbp)
pushq $fmtdec
call printf
add $16, %rsp

至

mov $fmtdec,%rdi
mov -8(%rbp),%rsi
xor %eax, %eax
call printf

并考虑这会覆盖您以前在 RDI 中的“返回值”。