如何编写一个信号处理程序来捕捉 SIGSEGV？

我想写一个信号处理程序来捕捉 SIGSEGV。 我使用。保护一块内存用于读或写

char *buffer;
char *p;
char a;
int pagesize = 4096;


mprotect(buffer,pagesize,PROT_NONE)

这将保护从缓冲区开始的内存的页大小字节，防止任何读或写操作。

其次，我试着读出那段记忆:

p = buffer;
a = *p

这将生成一个 SIGSEGV，并调用我的处理程序。 目前为止还不错。我的问题是，一旦调用了处理程序，我希望通过执行

mprotect(buffer,pagesize,PROT_READ);

并继续正常运行我的代码。我不想退出函数。 在以后对同一内存的写操作中，我希望再次捕获信号并修改写权限，然后记录该事件。

以下是 密码:

#include <signal.h>
#include <stdio.h>
#include <malloc.h>
#include <stdlib.h>
#include <errno.h>
#include <sys/mman.h>


#define handle_error(msg) \
do { perror(msg); exit(EXIT_FAILURE); } while (0)


char *buffer;
int flag=0;


static void handler(int sig, siginfo_t *si, void *unused)
{
printf("Got SIGSEGV at address: 0x%lx\n",(long) si->si_addr);
printf("Implements the handler only\n");
flag=1;
//exit(EXIT_FAILURE);
}


int main(int argc, char *argv[])
{
char *p; char a;
int pagesize;
struct sigaction sa;


sa.sa_flags = SA_SIGINFO;
sigemptyset(&sa.sa_mask);
sa.sa_sigaction = handler;
if (sigaction(SIGSEGV, &sa, NULL) == -1)
handle_error("sigaction");


pagesize=4096;


/* Allocate a buffer aligned on a page boundary;
initial protection is PROT_READ | PROT_WRITE */


buffer = memalign(pagesize, 4 * pagesize);
if (buffer == NULL)
handle_error("memalign");


printf("Start of region:        0x%lx\n", (long) buffer);
printf("Start of region:        0x%lx\n", (long) buffer+pagesize);
printf("Start of region:        0x%lx\n", (long) buffer+2*pagesize);
printf("Start of region:        0x%lx\n", (long) buffer+3*pagesize);
//if (mprotect(buffer + pagesize * 0, pagesize,PROT_NONE) == -1)
if (mprotect(buffer + pagesize * 0, pagesize,PROT_NONE) == -1)
handle_error("mprotect");


//for (p = buffer ; ; )
if(flag==0)
{
p = buffer+pagesize/2;
printf("It comes here before reading memory\n");
a = *p; //trying to read the memory
printf("It comes here after reading memory\n");
}
else
{
if (mprotect(buffer + pagesize * 0, pagesize,PROT_READ) == -1)
handle_error("mprotect");
a = *p;
printf("Now i can read the memory\n");


}
/*  for (p = buffer;p<=buffer+4*pagesize ;p++ )
{
//a = *(p);
*(p) = 'a';
printf("Writing at address %p\n",p);


}*/


printf("Loop completed\n");     /* Should never happen */
exit(EXIT_SUCCESS);
}

问题是，只有信号处理程序运行，我不能返回到主函数后捕捉到的信号。