编程耻辱柱

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此文记录了 各种耐人寻味的BUG

此BUG的定位， 耗时5天

栈数值覆盖

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[root@localhost source]# cat main.c
#include "string.h"
#include "stdio.h"

int fun_B(int a, int b, void* context)
{
    char *str = (char*)context;

    const char *p = "World Hello World Hello";

    strncpy(str, p, strlen(p));

    return 0;
}

int fun_A(int a, int b, int (*callback)(int a, int b, void *context), void *context)
{

    callback(a, b , &context);

    printf("a=%u b=%u\n", a ,b);

    return 0;
}

int main(int size, char **list)
{
    char str[] = "Hello World";

    fun_A(1, 2,fun_B, str);

    return 0;
}

[root@localhost source]#

编译 & 运行

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[root@localhost source]# gcc main.c  &&  ./a.out
a=7302252 b=1699225700
[root@localhost source]#

符号位

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[root@localhost source]# cat main.c
#include <stdlib.h>
#include <stdio.h>

struct test {
    int x : 1;
    int y : 31;
};

int main()
{
    struct test t ;
    t.x   = 1;

    if(1 == t.x)
    {
        printf("1\n");
    }
    else
    {
        printf("0\n");
    }

    return t.x;
}


[root@localhost source]#
[root@localhost source]# gcc main.c && ./a.out ; echo $?
0
255
[root@localhost source]#
[root@localhost source]#

C++的函数重载

问题 找不到add符号

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[root@localhost ~]# cat a.c
extern "C" {
    int add(int *a, int *b);

}

int add(const int *a, int *b)
{
    return *a + *b;
}
[root@localhost ~]# g++ -c a.c ; nm -Aa a.o
a.o:0000000000000000 a a.c
a.o:0000000000000000 b .bss
a.o:0000000000000000 n .comment
a.o:0000000000000000 d .data
a.o:0000000000000000 r .eh_frame
a.o:0000000000000000 n .note.GNU-stack
a.o:0000000000000000 t .text
a.o:0000000000000000 T _Z3addPKiPi
[root@localhost ~]#

解决 函数的申明不一致

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[root@localhost ~]# cat a.c
extern "C" {
    int add(int *a, int *b);

}

int add(int *a, int *b)
{
    return *a + *b;
}
[root@localhost ~]# g++ -c a.c ; nm -Aa a.o
a.o:0000000000000000 a a.c
a.o:0000000000000000 T add
a.o:0000000000000000 b .bss
a.o:0000000000000000 n .comment
a.o:0000000000000000 d .data
a.o:0000000000000000 r .eh_frame
a.o:0000000000000000 n .note.GNU-stack
a.o:0000000000000000 t .text
[root@localhost ~]#