c - 有符号整数的未定义行为和 Apple 安全编码指南

Question

Apple Secure Coding Guide说如下(第 27 页):

Also, any bits that overflow past the length of an integer variable (whether signed or unsigned) are dropped.

然而，关于有符号整数溢出C standard (89)说:

An example of undefined behavior is the behavior on integer overflow.

和

If an exception occurs during the evaluation of an expression (that is, if the result is not mathematically defined or not representable), the behavior is undefined.

编码指南错了吗？这里有什么我不明白的吗？我自己不相信 Apple Secure 编码指南会出错。

Answer 1

这是第二个意见，来自静态分析器described作为检测未定义的行为:

int x;

int main(){
  x = 0x7fffffff + 1;
}

分析器是这样运行的:

$ frama-c -val -machdep x86_32 t.c

它产生:

[kernel] preprocessing with "gcc -C -E -I.  t.c"
[value] Analyzing a complete application starting at main
...
t.c:4:[kernel] warning: signed overflow. assert 0x7fffffff+1 ≤ 2147483647;
...
[value] Values at end of function main:
  NON TERMINATING FUNCTION

这意味着程序 t.c 包含未定义的行为，并且它的执行不会在不导致未定义行为的情况下终止。