文章目錄
- 函數描述
- 函數使用
- 抓取發送信号的程序資訊
mark一次擷取核心信号,并作相應處理的手段
linux核心中斷機制的一個重要實作就是信号。信号使得核心和使用者态的互動更加便捷,這個便捷對開發者來說可以更好的利用系統原生核心來處理資訊。
《深入了解unix核心》中對信号作用的描述如下:
- 讓程序知道已經發生了一個特定事件
- 強迫程序執行它自己代碼中的信号處理程式
這裡主要描述一下借用sigaction系統調用,對信号進行注冊并做出相應的處理
函數描述
包含頭檔案:
#include <signal.h>
函數原型:
int sigaction(int signum, const struct sigaction *act,struct sigaction *oldact);
參數含義如下:
-
表示特例化信号代表的數字,其中signum
和SIGKILL
信号不能被注冊SIGSTOP
-
該資料結構如下struct sigaction
struct sigaction {
void (*sa_handler)(int); /*表示要執行操作的類型,它的值可以是指向信号處理程式的一個指針
,SIG_DFL(值為0,指定預設操作,
或者SIG_IBN(值為1,指定忽略信号)*/
void (*sa_sigaction)(int, siginfo_t *, void *);
sigset_t sa_mask; /*這是一個标志集,制定必須怎樣處理信号。*/
int sa_flags; /*這個是類型為sigset_t的變量,指定當運作信号處理程式時要屏蔽的信号,一般為SA_SIGINFO,來擷取處理程式的附件資訊*/
void (*sa_restorer)(void);
};
-
這裡一般是我們在程式中封裝該sigaction資料結構,将我們想要的參數封裝好傳入進去,再通過系統調用執行處理。
其中SA_SIGINFO資料結構包含如下參數,直接通過siginfo_t 的結構體變量來擷取
siginfo_t {
int si_signo; /* Signal number */
int si_errno; /* An errno value */
int si_code; /* Signal code */
int si_trapno; /* Trap number that caused
hardware-generated signal
(unused on most architectures) */
pid_t si_pid; /* Sending process ID */
uid_t si_uid; /* Real user ID of sending process */
int si_status; /* Exit value or signal */
clock_t si_utime; /* User time consumed */
clock_t si_stime; /* System time consumed */
sigval_t si_value; /* Signal value */
int si_int; /* POSIX.1b signal */
void *si_ptr; /* POSIX.1b signal */
int si_overrun; /* Timer overrun count; POSIX.1b timers */
int si_timerid; /* Timer ID; POSIX.1b timers */
void *si_addr; /* Memory location which caused fault */
long si_band; /* Band event (was int in
glibc 2.3.2 and earlier) */
int si_fd; /* File descriptor */
short si_addr_lsb; /* Least significant bit of address
(since Linux 2.6.32) */
}
-
該參數非空的,存儲最新的一個action的資訊的資料結構const struct sigaction *act
-
該參數也為空,同時存儲上一個action的資訊的資料結構struct sigaction *oldact
函數使用
檢視如下代碼
#include <sys/types.h>
#include <unistd.h>
#include <stdio.h>
#include <signal.h>
#include <sys/time.h>
#include <time.h>
void get_unlegal_memory()
{
char *a = NULL;
/*未配置設定空間,模拟非法通路記憶體*/
printf("get the unmalloc memmory %c!\n",a[0]);
}
void print_stacktrace()
{
int size = 16,i=0;
void * array[16];
int stack_num = backtrace(array, size);
char ** stacktrace = backtrace_symbols(array, stack_num);
for (; i < stack_num; ++i)
{
printf("%s\n", stacktrace[i]);
}
free(stacktrace);
}
void sig_op(int signo, siginfo_t* info, void* context)
{
print_stacktrace();
printf("get the kernel signal\n");
printf("sig signo is %d\n",info->si_signo);
exit(0);
}
int main(int argc,char** argv)
{
struct sigaction act;
struct sigaction oact;
pid_t pid;
pid=getpid();
sigemptyset(&act.sa_mask);
/*注冊信号處理函數如下,sig_op,用來列印函數調用棧以及信号集中發出該信号的程序詳細資訊*/
act.sa_handler=sig_op;
act.sa_flags=SA_SIGINFO;
/*注冊了信号SIGSEGV用來擷取非法記憶體通路*/
if(sigaction(SIGSEGV,&act,&oact)== -1)
printf("%d","install error~!\n",SIGSEGV);
printf("the pid is %d\n",pid);
get_unlegal_memory();
return 0;
}
編譯方式如下
gcc test.c -rdynamic -g -o test
這裡增加了列印函數調用棧,需要将所有符号連接配接到二進制檔案,是以需要
-rdynamic
參數,這裡想要進一步了解列印函數調用棧,可以參考關于ceph源碼 backtrace 列印函數調用棧
執行結果如下可以看到函數調用棧如下,sig_op函數是由系統c庫發出
./test
the pid is 7754
./test_memory(print_stacktrace+0x32) [0x400b2b]
./test_memory(sig_op+0x1d) [0x400ba5]
/lib64/libc.so.6(+0x35a00) [0x7f470de32a00]
./test_memory(get_unlegal_memory+0x20) [0x400ae0]
./test_memory(main+0x9c) [0x400c6c]
/lib64/libc.so.6(__libc_start_main+0xf5) [0x7f470de1eaf5]
./test_memory() [0x4009f9]
get the kernel signal
sig signo is 11
抓取發送信号的程序資訊
#include <sys/types.h>
#include <unistd.h>
#include <stdio.h>
#include <signal.h>
#include <sys/time.h>
#include <time.h>
/*列印目前時間*/
void printDatetime()
{
time_t now;
struct tm *tm_now;
time(&now);
tm_now = localtime(&now);
printf("now datetime: %d-%d-%d %d:%d:%d\n", tm_now->tm_year, tm_now->tm_mon, tm_now->tm_mday, tm_now->tm_hour, tm_now->tm_min, tm_now->tm_sec);
fflush(stdout);
}
#define BUF_SIZE 1024
/*列印發送信号程序的詳細資訊,即從/proc/p_id/status 檔案目錄下擷取*/
void printTaskStatusByPid(int pid) {
char proc_pid_path[BUF_SIZE]={0};
char buf[BUF_SIZE]={0};
sprintf(proc_pid_path, "/proc/%d/status", pid);
FILE* fp = fopen(proc_pid_path, "r");
if(NULL != fp){
while(fgets(buf, BUF_SIZE-1, fp)!= NULL){
printf("%s\n",buf);
}
fclose(fp);
}
else
{
printf("NULL\n");
}
}
/*列印函數調用棧*/
void print_stacktrace()
{
int size = 16,i=0;
void * array[16];
int stack_num = backtrace(array, size);
char ** stacktrace = backtrace_symbols(array, stack_num);
for (; i < stack_num; ++i)
{
printf("%s\n", stacktrace[i]);
}
free(stacktrace);
}
/*核心信号處理函數,列印發送該信号的程序資訊*/
void sig_op(int signo, siginfo_t* info, void* context)
{
print_stacktrace();
printf("the signo is %d\n",signo);
printf("sig pid is %d\n", (int)(info->si_pid));
printf("sig uid is %d\n", (int)(info->si_uid));
printf("sig signo is %d\n",info->si_signo);
printTaskStatusByPid((int)(info->si_pid));
fflush(stdout);
}
int main(int argc,char** argv)
{
struct sigaction act;
struct sigaction oact;
pid_t pid;
pid=getpid();
printDatetime();
printf("the pid is %d\n",pid);
fflush(stdout);
/*初始化sigset_t變量中的位*/
sigemptyset(&act.sa_mask);
act.sa_handler=sig_op;
act.sa_flags=SA_SIGINFO;
/*注冊信号*/
if(sigaction(SIGINT,&act,&oact)==-1)
printf("%s","install error~!\n");
if(sigaction(SIGTERM,&act,&oact)==-1)
printf("%s","install error~!\n");
if(sigaction(SIGSEGV,&act,&oact)== -1)
printf("%d","install error~!\n",SIGSEGV);
/*死循環來列印時間,當遇到注冊的核心資訊,此時列印出程序詳細資訊*/
while(1)
{
sleep(1);
printDatetime();
fflush(stdout);
}
return 0;
}
now datetime: 119-6-13 19:44:29
now datetime: 119-6-13 19:44:30
#執行了killall操作,擷取到了SIGTERM信号,列印出來的資訊
./test(print_stacktrace+0x32) [0x400e86]
./test(sig_op+0x1d) [0x400f00]
/lib64/libc.so.6(+0x35a00) [0x7f18223b9a00]
/lib64/libc.so.6(nanosleep+0x10) [0x7f1822441890]
/lib64/libc.so.6(sleep+0xd4) [0x7f1822441744]
./test(main+0x109) [0x401083]
/lib64/libc.so.6(__libc_start_main+0xf5) [0x7f18223a5af5]
./test() [0x400c49]
the signo is 15
sig pid is 20863
sig uid is 0
sig signo is 15
#可以看到發送SIGTERM信号的程序名稱如下
Name: killall
State: R (running)
Tgid: 20863
Ngid: 0
Pid: 20863
PPid: 15099
TracerPid: 0
Uid: 0 0 0 0
Gid: 0 0 0 0
FDSize: 256
Groups: 0
VmPeak: 116760 kB
VmSize: 116760 kB
VmLck: 0 kB
VmPin: 0 kB
VmHWM: 924 kB
VmRSS: 924 kB
VmData: 212 kB
VmStk: 136 kB
VmExe: 20 kB
VmLib: 2508 kB
VmPTE: 64 kB
VmSwap: 0 kB
Threads: 1
SigQ: 1/125771
SigPnd: 0000000000000000
ShdPnd: 0000000000000000
SigBlk: 0000000000000000
SigIgn: 0000000000000000
SigCgt: 0000000180000000
CapInh: 0000000000000000
CapPrm: 0000001fffffffff
CapEff: 0000001fffffffff
CapBnd: 0000001fffffffff
Seccomp: 0
Cpus_allowed: ff
Cpus_allowed_list: 0-7
Mems_allowed: 00000000,00000000,00000000,00000000,00000000,00000000,00000000,00000000,00000000,00000000,00000000,00000000,00000000,00000000,00000000,00000000,00000000,00000000,00000000,00000000,00000000,00000000,00000000,00000000,00000000,00000000,00000000,00000000,00000000,00000000,00000000,00000001
Mems_allowed_list: 0
voluntary_ctxt_switches: 1
nonvoluntary_ctxt_switches: 1
now datetime: 119-6-13 19:44:30
now datetime: 119-6-13 19:46:45
now datetime: 119-6-13 19:46:46
#執行鍵盤中斷擷取到信号資訊,但是該執行并不是一個程序,是以并不會列印調用棧
^C./test(print_stacktrace+0x32) [0x400e86]
./test(sig_op+0x1d) [0x400f00]
/lib64/libc.so.6(+0x35a00) [0x7f18223b9a00]
/lib64/libc.so.6(nanosleep+0x10) [0x7f1822441890]
/lib64/libc.so.6(sleep+0xd4) [0x7f1822441744]
./test(main+0x109) [0x401083]
/lib64/libc.so.6(__libc_start_main+0xf5) [0x7f18223a5af5]
./test() [0x400c49]
the signo is 2
sig pid is 0
sig uid is 0
sig signo is 2
NULL
now datetime: 119-6-13 19:46:47
now datetime: 119-6-13 19:48:10
now datetime: 119-6-13 19:48:11
#當執行了kill -9 指令時,即發送SIGKILL信号,會徹底終止目前程序。(SIGKILL信号不允許被注冊,抓取)
Killed