如何使用＆QUOT; SIGALTSTACK＆QUOT;在信号处理程序？ [英] how to use "sigaltstack" in signal handler program?

问题描述

做谁知道如何使用 SIGALTSTACK 在一个真实的信号处理程序，简单但完整的code可以对我帮助很大！
预先感谢您！

did anyone who knows how to use the sigaltstack in a real signal handler program,a simple but complete code may be great help to me! thank you in advance!

推荐答案

下面是一个使用 SIGALTSTACK 赶上无限递归最小的示例程序。如果您注释掉 SIGALTSTACK 来电或 SA_ONSTACK 标志，信号处理程序将无法运行，因为它没有栈左，程序会崩溃。

Here is a minimal sample program that uses sigaltstack to catch infinite recursion. If you comment out the sigaltstack call or SA_ONSTACK flag, the signal handler will not be able to run because it has no stack left and the program will just crash.

#define _XOPEN_SOURCE 700
#include <signal.h>
#include <unistd.h>
void handler(int sig)
{
    write(2, "stack overflow\n", 15);
    _exit(1);
}
unsigned infinite_recursion(unsigned x) {
    return infinite_recursion(x)+1;
}
int main()
{
    static char stack[SIGSTKSZ];
    stack_t ss = {
        .ss_size = SIGSTKSZ,
        .ss_sp = stack,
    };
    struct sigaction sa = {
        .sa_handler = handler,
        .sa_flags = SA_ONSTACK
    };
    sigaltstack(&ss, 0);
    sigfillset(&sa.sa_mask);
    sigaction(SIGSEGV, &sa, 0);
    infinite_recursion(0);
}

一个更复杂的使用可能会实际执行 siglongjmp 跳出信号处理和回哪里可避免无限递归的一个点。如果正在使用异步信号不安全库调用这是无效的，或者如果你的数据可能会在一个不安全/不可恢复的状态留，但如果你正在执行的纯算术计算，也可能是有效的。

A more sophisticated use might actually perform siglongjmp to jump out of the signal handler and back to a point where the infinite recursion can be avoided. This is not valid if async-signal-unsafe library calls are being used, or if your data might be left in an unsafe/unrecoverable state, but if you're performing pure arithmetic computations, it may be valid.

也许对于信号处理一个更好的任务将是执行，这不是已经保存到磁盘上任何有价值/关键数据的紧急转储。这可能是困难的，如果你不能叫异步信号不安全的功能，但如果你把一些精力它通常是可能的。

Perhaps a better task for the signal handler would be performing an emergency dump of any valuable/critical data that wasn't already saved to disk. This could be difficult if you can't call async-signal-unsafe functions, but it's usually possible if you put some effort into it.

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