What is coredump
How to analyse coredump
Why program coredump
- memory overload
- using thread-unsafe functions on multi-thread
- not using lock when read-write data in multi-thread
- invalid point
- stack overload
How to use core file
- allow to generate core file
ulimit –c unlimitedecho /tmp/core.%e.%p > /proc/sys/kernel/core_patterngcc –g core_dump_test.c -o core_dump_test, must used -g to build.
- get core file
- debug
gdb ./test /tmp/corebtf 3p buffer
Signal of core
Examples
write data to protected memory
#include <stdio.h>
int main(){
int i=0;
scanf("%d",i);
printf("%d\n",i);
return 0;
}
#include <stdio.h>
int main(){
char *p;
p = NULL;
*p = 'x';
printf("%c", *p);
return 0;
}
memory overflow (array overflow, variable type different and so on)
#include <stdio.h>
int main(){
char test[1];
printf("%c", test[1000000000]);
return 0;
}
Access to a not exist address
#include <stdio.h>
int main(){
int b = 10;
printf("%s\n", b);
return 0;
}
#include <stdio.h>
#include <string.h>
int main(){
char c='c';
int i=10;
char buf[100];
printf("%s", c); //试图把char型按照字符串格式输出，这里的字符会解释成整数，
//再解释成地址，所以原因同上面那个例子
printf("%s", i); //试图把int型按照字符串输出
memset(buf, 0, 100);
sprintf(buf, "%s", c); 试图把char型按照字符串格式转换
memset(buf, 0, 100);
sprintf(buf, "%s", i);//试图把int型按照字符串转换
}
- Other, likes:
- Initialization when defined point, check point before using.
- Careful array index
- check if success when do
pthread_create, if fail and do pthread_join for
this thread will occur segment fault
Auto start gdb when core occur
#include <stdio.h>
#include <stdlib.h>
#include <signal.h>
#include <string.h>
#include <sys/types.h>
#include <unistd.h>
void dump(int signo)
{
char buf[1024];
char cmd[1024];
FILE *fh;
snprintf(buf, sizeof(buf), "/proc/%d/cmdline", getpid());
if(!(fh = fopen(buf, "r")))
exit(0);
if(!fgets(buf, sizeof(buf), fh))
exit(0);
fclose(fh);
if(buf[strlen(buf) - 1] == '\n')
buf[strlen(buf) - 1] = '\0';
snprintf(cmd, sizeof(cmd), "gdb %s %d", buf, getpid());
system(cmd);
exit(0);
}
void dummy_function (void)
{
unsigned char *ptr = 0x00;
*ptr = 0x00;
}
int main (void)
{
signal(SIGSEGV, &dump);
dummy_function ();
return 0;
}
Reference