c - 带有 C 段错误的汇编函数

Question

我正在尝试制作使用 SSE 和 FPU 进行并行计算的汇编函数。不幸的是，我收到了 segmentation fault(core dumped) 错误(调试时它没有显示在汇编函数中)。我也无法退出汇编功能。 gdb 显示:

Warning:
Cannot insert breakpoint 0.
Cannot access memory at address 0x2bffff

在 ret 语句之后。我不知道是什么导致了这种行为。也许你们中有些人看到了我没有看到的东西？干杯。

积分.s

#float intgr_vert(float x)
#{
#   return pow(x, 2) - 4*x + 6;
#}

s_precision = 0x007f

.bss
    .lcomm holder, 4
    .lcomm  rect_size_vec, 16
    .lcomm  x_vec, 16
    .lcomm  result, 16

.data
four:
    .float 4.0, 4.0, 4.0, 4.0
six:
    .float 6.0, 6.0, 6.0, 6.0

.globl four_intgr_strips

.type four_intgr_strips, @function
four_intgr_strips:

pushl %eax
pushl %ecx
pushl %edx
pushl %ebp
movl  %esp, %ebp

subl $2, %esp  

movl $0, %edi
movl 20(%ebp),  %eax    #x position
movl 24(%ebp), %ebx #rectangle size
movw $s_precision, -2(%ebp)

finit

fldcw -2(%ebp)

pool:
movl %eax, x_vec(, %edi, 4)
movl %ebx, rect_size_vec(, %edi, 4)

movl %eax, holder
flds holder
movl %ebx, holder
flds holder     #adding size of rectangle to calculate different x
fadd %st(1), %st(0)
fstps holder
movl holder, %eax

inc %edi
cmp $4, %edi
je pool_dne
jmp pool

pool_dne:


ret ###########################can't go further

.type sumAreas, @function
sumAreas:
movl $0, %edi

flds result(, %edi, 4)
inc %edi

loop:
flds result(, %edi, 4)
fadd %st(1), %st(0)
inc %edi
cmp $4, %edi
je end_loop
jmp loop

end_loop:


ret

.type calcAreas, @function
calcAreas:

movaps rect_size_vec, %xmm1
mulps %xmm1, %xmm0
movaps %xmm0, result

ret

.type calcVertical, @function
calcVertical:

movaps x_vec, %xmm0
mulps %xmm0, %xmm0
movaps x_vec, %xmm1
movups four, %xmm2
mulps %xmm1, %xmm2
subps %xmm2, %xmm0
movups six, %xmm1
addps %xmm1, %xmm0

ret

主.c

#include <stdio.h>
#include <math.h>

// x^2 - 4x + 6 integral

float four_intgr_strips(float, float);


float calc_intgr_in_as(int a, int n, float rect_size)
{
    float sum = 0;
    float four_rect_area;
    float last_rect_l_corner = a;

for(int i = 0; i != n/4; i++)
{
        four_rect_area = four_intgr_strips(last_rect_l_corner, rect_size);
        sum = sum + four_rect_area;
        last_rect_l_corner = last_rect_l_corner + 4*rect_size;
    }


return sum;
}

int main()
{
    int a, b, n;
    float rect_size;
    float sum;

    printf("\nType integral lower bound:");
    scanf("%d", &a);
    printf("\nType integral upper bound:");

 scanf("%d", &b);
    do
    {
        printf("\nType rectangles number(must be multiple of 4):");
        scanf("%d", &n);
    }
    while(n % 4 != 0);

    rect_size = (float)(b - a)/n;

    sum = calc_intgr_in_as(a, n, rect_size);
    printf("\nArea under function is: %f with SSE", sum);
}

Answer 1

您忘记清理堆栈。在序言中你有:

pushl %eax
pushl %ecx
pushl %edx
pushl %ebp
movl  %esp, %ebp

您显然需要在ret 之前撤消它，例如:

movl %ebp, %esp
popl %ebp
popl %edx
popl %ecx
popl %eax
ret

PS:我已经告诉过你，不对齐堆栈是个坏主意，迟早会害了你。此外，下次您提问时，请提及您使用的输入以及您期望的输出。