c - 检测传递指向未初始化变量的指针

Question

有些函数有一个指针参数，指向结果来自哪里应存储调用函数，但函数还要求调用函数时，此指针指向用作输入值的某个值(例如输入/输出参数)。

我想检测调用此类函数并指向未初始化变量的情况。 Coccinelle应该能够做到这一点，但是我为实现这一目标而努力了一点。

示例目标代码:

#include <string.h>
#include <stdio.h>

static void cartoon_random_generator(int *n)
{
    switch (*n) {
    case 4:
        *n = 4; /* http://xkcd.com/221/ */
        break;
    case 9:
        *n = 9; /* http://dilbert.com/strips/comic/2001-10-25/ */
        break;
    default:
        fprintf(stderr, "*n was not initialized before calling this function\n");
        break;
    }
}
/* alternative links http://i.stack.imgur.com/VvTef.png and http://i.stack.imgur.com/u0iJ7.gif */

static void test(const char *cartoon)
{
    // not ok, missing
    {
        int n1;

        cartoon_random_generator(&n1);
        printf("Random number = %d\n", n1);
    }

    // ok, declaration
    {
        int n2 = 4;

        cartoon_random_generator(&n2);
        printf("Random number = %d\n", n2);
    }

    // ok, statement
    {
        int n3;

        n3 = 9;
        cartoon_random_generator(&n3);
        printf("Random number = %d\n", n3);
    }

    // both ok and not ok
    {
        int n4, n9;

        n9 = 9;
        //strcmp(cartoon, "XKCD") == 0 ? cartoon_random_generator(&n4) : cartoon_random_generator(&n9);
        if (strcmp(cartoon, "XKCD") == 0)
            cartoon_random_generator(&n4);
        else
            cartoon_random_generator(&n9);
        printf("Random numbers = %d, %d\n", n4, n9);
    }
}

我写了下面的七星脚本

/* It is an error to call cartoon_random_generator with an uninitialized
   variable. Detect this. */


/*
 * This rule matches an OK case where the in variable is initialized when
 * declared. No action is performed for this rule other than giving p1 a value.
 */
@rule1@
position p1;
expression init_expression;
identifier n;
@@

int n = init_expression;
...
cartoon_random_generator@p1(&n)


/*
 * This rule matches an OK case where the in variable is initialized in a
 * separate statement. No action is performed for this rule other than
 * giving p2 a value.
 */
@rule2@
position p2;
expression init_expression;
identifier n;
@@

int n;
...
n = init_expression;
...
cartoon_random_generator@p2(&n)


/* If neither rule1 or rule2 have matched so far,
 * we have a variable that is uninitialized. */

@rule3@
position p3 != rule1.p1, rule2.p2;
identifier n;
@@

int n;
...
* cartoon_random_generator@p3(&n)

但是没有考虑规则 2，我不明白为什么。运行它给出:

$ /opt/coccinelle/bin/spatch -sp_file cartoon_random.cocci cartoon_random.c
init_defs_builtins: /opt/coccinelle/share/coccinelle/standard.h
warning: rule3: inherited metavariable p2 not used in the -, +, or context code
HANDLING: cartoon_random.c
diff =
--- cartoon_random.c
+++ /tmp/cocci-output-7916-8df75b-cartoon_random.c
@@ -23,7 +23,6 @@ static void test(const char *cartoon)
        {
                int n1;

-               cartoon_random_generator(&n1);
                printf("Random number = %d\n", n1);
        }

@@ -40,7 +39,6 @@ static void test(const char *cartoon)
                int n3;

                n3 = 9;
-               cartoon_random_generator(&n3);
                printf("Random number = %d\n", n3);
        }

@@ -51,9 +49,7 @@ static void test(const char *cartoon)
                n9 = 9;
                //strcmp(cartoon, "XKCD") == 0 ? cartoon_random_generator(&n4) : cartoon_random_generator(&n9);
                if (strcmp(cartoon, "XKCD") == 0)
-                       cartoon_random_generator(&n4);
                else
-                       cartoon_random_generator(&n9);
                printf("Random numbers = %d, %d\n", n4, n9);
        }
 }

Answer 1

我完全是 Coccinelle 用法的初学者，一直想了解它。您提出的问题是检测未初始化变量的一个相当好的要求，这让我进行了一些研究。在做了一些研究之后(& 从 warning: rule3: inherited metavariable p2 not used in the -, +, or context code 中得到线索)其中一种方法(可能有其他/更好的方法) 使你的 coccinelle 脚本工作是结合规则 1 和 2 & 在最终规则中仅对元变量使用单一继承。这些线路上的东西:

@rule1@
position p1;
expression init_expression;
identifier n;
@@

(
int n = init_expression;
|
int n;
...
n = init_expression;
)
...
cartoon_random_generator@p1(&n)

@rule2@
position p2 != rule1.p1;
identifier n;
@@

int n;
...
* cartoon_random_generator@p2(&n)  

在这种情况下看到的输出是:

$spatch -sp_file cartoon_random.cocci cartoon_random.c
init_defs_builtins: /usr/share/coccinelle/standard.h
HANDLING: cartoon_random.c
diff =
--- cartoon_random.c
+++ /tmp/cocci-output-7916-8df75b-cartoon_random.c
@@ -23,7 +23,6 @@ static void test(const char *cartoon)
        {
                int n1;

-               cartoon_random_generator(&n1);
                printf("Random number = %d\n", n1);
        }

@@ -51,9 +50,6 @@ static void test(const char *cartoon)
                n9 = 9;
                //strcmp(cartoon, "XKCD") == 0 ? cartoon_random_generator(&n4) : cartoon_random_generator(&n9);
                if (strcmp(cartoon, "XKCD") == 0)
-                       cartoon_random_generator(&n4);
                else
                        cartoon_random_generator(&n9);
                printf("Random numbers = %d, %d\n", n4, n9);

这是在 FC15 上运行的，使用从 Fedora 存储库安装的 coccinelle 软件包。
希望这对您有所帮助!