如何警告超出范围的局部变量的指针 [英] How to be warned about pointers to out-of-scope local variables

问题描述

考虑以下代码:

#include <stdio.h>

void badidea(int**);

int main(void) {
        int* p;
        badidea(&p);
        printf("%d\n", *p); /* undefined behavior happens here: p points to x from badidea, which is now out of scope */
        return 0;
}

void badidea(int** p) {
        int x = 5;
        *p = &x;
}

其意图似乎是将打印5，但是由于取消引用main中范围外的局部变量的指针，因此它实际上会调用未定义的行为.如何在代码库中找到此问题的实例?到目前为止，这是我尝试过的:

The intent seems to be that it will print 5, but it actually invokes undefined behavior, due to dereferencing a pointer to an out-of-scope local variable in main. How can I find instances of this problem in a codebase? Here's what I've tried so far:

• 使用gcc -Wall -Wextra -pedantic
进行编译
• 使用clang -Weverything
进行编译
• 运行时已使用clang -fsanitize=undefined
进行了编译
• 在valgrind
下运行

• Compiling with gcc -Wall -Wextra -pedantic
• Compiling with clang -Weverything
• Running having compiled with clang -fsanitize=undefined
• Running under valgrind

以上均未产生任何警告.

None of the above produced any warnings.

推荐答案

首先使用GCC 7.2和在没有 -fsanitize=address 和的情况下进行编译，然后在Valgrind下运行会产生以下结果:

Compiling first with GCC 7.2 and without -fsanitize=address and then running under Valgrind produces the following:

==25751== Conditional jump or move depends on uninitialised value(s)
==25751==    at 0x4E988DA: vfprintf (vfprintf.c:1642)
==25751==    by 0x4EA0F25: printf (printf.c:33)
==25751==    by 0x1086E5: main (in ./a.out)

其次是其他警告.

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