至少對於Linux、FreeBSD、Solaris、AIX這四種作業系統，有一種辦法。不要安裝傳
統sa_handler訊號控制程式碼，而是安裝sa_sigaction訊號控制程式碼。細節請man sigaction並
參照標頭檔案加強理解。下面是一個可移植演示程式。
--------------------------------------------------------------------------
/*
* For x86/Linux RedHat_8 2.4.18-14
* For x86/FreeBSD 4.5-RELEASE
* For SPARC/Solaris 8
* For AIX 4.3.3.0
*
* gcc -Wall -pipe -O3 -s -o siginfo_test siginfo_test.c
*/
/************************************************************************
* *
* Head File *
* *
************************************************************************/
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <strings.h>
#include <signal.h>
#include <unistd.h>
#include <setjmp.h>
#include <sys/time.h>
/************************************************************************
* *
* Macro *
* *
************************************************************************/
/*
* for signal handlers
*/
typedef void Sigfunc ( int, siginfo_t *, void * );
#define PRIVATE_SIG_ERR ((Sigfunc *)-1)
/************************************************************************
* *
* Function Prototype *
* *
************************************************************************/
static void Atexit ( void ( * func ) ( void ) );
static void init_signal ( void );
static void init_timer ( unsigned int s );
static void on_alarm ( int signo, siginfo_t *si, void *unused );
static void on_segvbus ( int signo, siginfo_t *si, void *unused );
static void on_terminate ( int signo, siginfo_t *si, void *unused );
static Sigfunc * PrivateSignal ( int signo, Sigfunc *func );
static int Setitimer ( int which,
struct itimerval *value,
struct itimerval *ovalue );
static Sigfunc * Signal ( int signo, Sigfunc *func );
static void terminate ( void );
/************************************************************************
* *
* Static Global Var *
* *
************************************************************************/
static sigjmp_buf jmpbuf;
static volatile sig_atomic_t canjump = 0;
/************************************************************************/
static void Atexit ( void ( * func ) ( void ) )
{
if ( atexit( func ) != 0 )
{
exit( EXIT_FAILURE );
}
return;
} /* end of Atexit */
/*
* 初始化訊號控制程式碼
*/
static void init_signal ( void )
{
unsigned int i;
Atexit( terminate );
for ( i = 1; i < 9; i++ )
{
Signal( i, on_terminate );
}
Signal( SIGTERM, on_terminate );
Signal( SIGALRM, on_alarm );
Signal( SIGSEGV, on_segvbus );
Signal( SIGBUS , on_segvbus );
return;
} /* end of init_signal */
/*
* 我們的定時器精度只支援到秒
*/
static void init_timer ( unsigned int s )
{
struct itimerval value;
value.it_value.tv_sec = s;
value.it_value.tv_usec = 0;
/*
* 只生效一次
*/
value.it_interval.tv_sec = 0;
value.it_interval.tv_usec = 0;
Setitimer( ITIMER_REAL, &value, NULL );
return;
} /* end of init_timer */
static void on_alarm ( int signo, siginfo_t *si, void *unused )
{
fprintf
(
stderr,
"/n"
"signo = %d/n"
"si = 0x%08X/n"
"unused = 0x%08X/n",
signo,
( unsigned int )si,
( unsigned int )unused
);
if ( NULL != si )
{
fprintf
(
stderr,
"si->si_signo = %d/n"
"si->si_errno = %d/n"
"si->si_code = %d/n"
"si->si_pid = %u/n"
"si->si_uid = %u/n"
"si->si_status = %d/n"
"si->si_addr = 0x%08X/n",
si->si_signo,
si->si_errno,
si->si_code,
( unsigned int )si->si_pid,
( unsigned int )si->si_uid,
( int )si->si_status,
( unsigned int )si->si_addr
);
}
return;
} /* end of on_alarm */
static void on_segvbus ( int signo, siginfo_t *si, void *unused )
{
fprintf
(
stderr,
"/n"
"signo = %d/n"
"si = 0x%08X/n"
"unused = 0x%08X/n",
signo,
( unsigned int )si,
( unsigned int )unused
);
if ( NULL != si )
{
fprintf
(
stderr,
"si->si_signo = %d/n"
"si->si_errno = %d/n"
"si->si_code = %d/n"
"si->si_pid = %u/n"
"si->si_uid = %u/n"
"si->si_status = %d/n"
"si->si_addr = 0x%08X/n",
si->si_signo,
si->si_errno,
si->si_code,
( unsigned int )si->si_pid,
( unsigned int )si->si_uid,
( int )si->si_status,
( unsigned int )si->si_addr
);
}
if ( 0 == canjump )
{
/*
* unexpected signal, ignore
*/
return;
}
canjump = 0;
/*
* jump back to main, don't return
*/
siglongjmp( jmpbuf, signo );
} /* end of on_segvbus */
/*
* 參如下標頭檔案瞭解siginfo_t定義
*
* Linux /usr/include/bits/siginfo.h
* FreeBSD /usr/include/sys/signal.h
* Solaris /usr/include/sys/siginfo.h
* AIX /usr/include/sys/signal.h
*
* 第三形參不推薦使用，context相關。
*/
static void on_terminate ( int signo, siginfo_t *si, void *unused )
{
/*
* 就上四種OS而言，測試Solaris，執行siginfo_test，按Ctrl-C進入該流程時
* si為NULL，其他三種系統則不同。
*/
if ( NULL != si )
{
/*
* 演示用，不推薦在訊號控制程式碼中使用fprintf()
*/
fprintf
(
stderr,
"/n"
"signo = %d/n"
"si = 0x%08X/n"
"unused = 0x%08X/n"
"si->si_signo = %d/n"
"si->si_errno = %d/n"
"si->si_code = %d/n",
signo,
( unsigned int )si,
( unsigned int )unused,
si->si_signo,
si->si_errno,
si->si_code
);
/*
* si_code為SI_USER時意味著"signal sent by another process with kill()"
*
* 就上四種OS而言，我所測試的FreeBSD反應與其他三種不同，kill程式時
* si_code始終為0，而FreeBSD有如下定義:
*
* #define SI_USER 0x10001
*
* 如果不判斷si_code，強行顯示si_pid、si_uid，對於FreeBSD而言總是0。
* 下面出於方便演示目的，沒有判斷si_code。正確作法應該判斷si_code，
* 然後顯示聯合的不同成員。
*/
fprintf
(
stderr,
"si->si_pid = %u/n"
"si->si_uid = %u/n"
"si->si_status = %d/n"
"si->si_addr = 0x%08X/n",
( unsigned int )si->si_pid,
( unsigned int )si->si_uid,
( int )si->si_status,
( unsigned int )si->si_addr
);
}
else
{
fprintf
(
stderr,
"/n"
"signo = %d/n"
"si = 0x%08X/n"
"unused = 0x%08X/n",
signo,
( unsigned int )si,
( unsigned int )unused
);
}
/*
* 這次我們使用atexit()函式
*/
exit( EXIT_SUCCESS );
} /* end of on_terminate */
/*
* 與以前版本不同之處在於使用sa_sigaction，而不是sa_handler。
*/
static Sigfunc * PrivateSignal ( int signo, Sigfunc *func )
{
#if 0
from Linux /usr/include/bits/sigaction.h
struct sigaction
{
union
{
/*
* Used if SA_SIGINFO is not set.
*/
__sighandler_t sa_handler;
/*
* Used if SA_SIGINFO is set.
*/
void ( *sa_sigaction ) ( int, siginfo_t *, void * );
} __sigaction_handler;
#define sa_handler __sigaction_handler.sa_handler
#define sa_sigaction __sigaction_handler.sa_sigaction
/*
* Additional set of signals to be blocked.
*/
__sigset_t sa_mask;
/*
* Special flags.
*/
int sa_flags;
/*
* The sa_restorer element is obsolete and should not be used.
* POSIX does not specify a sa_restorer element.
*
* Restore handler.
*/
void ( *sa_restorer ) ( void );
};
#endif
struct sigaction act, oact;
memset( &act, 0, sizeof( act ) );
sigemptyset( &act.sa_mask );
/*
* Invoke signal-catching function with three arguments instead of one.
*/
act.sa_flags = SA_SIGINFO;
act.sa_sigaction = func;
if ( SIGALRM == signo )
{
#ifdef SA_INTERRUPT
/*
* SunOS 4.x
*/
act.sa_flags |= SA_INTERRUPT;
#endif
}
else
{
#ifdef SA_RESTART
/*
* SVR4, 4.4BSD
*/
act.sa_flags |= SA_RESTART;
#endif
}
if ( sigaction( signo, &act, &oact ) < 0 )
{
return( PRIVATE_SIG_ERR );
}
return( oact.sa_sigaction );
} /* end of PrivateSignal */
static int Setitimer ( int which, struct itimerval *value, struct itimerval *ovalue )
{
int ret;
if ( ( ret = setitimer( which, value, ovalue ) ) < 0 )
{
perror( "setitimer error" );
exit( EXIT_FAILURE );
}
return( ret );
} /* end of Setitimer */
static Sigfunc * Signal ( int signo, Sigfunc *func )
{
Sigfunc *sigfunc;
if ( PRIVATE_SIG_ERR == ( sigfunc = PrivateSignal( signo, func ) ) )
{
perror( "signal error" );
exit( EXIT_FAILURE );
}
return( sigfunc );
} /* end of Signal */
static void terminate ( void )
{
/*
* _exit( EXIT_SUCCESS );
*/
return;
} /* end of terminate */
int main ( int argc, char * argv[] )
{
/*
* for autovar, must be volatile
*/
volatile unsigned char *p;
init_signal();
p = ( unsigned char * )&p;
if ( 0 != sigsetjmp( jmpbuf, 1 ) )
{
printf
(
"p = 0x%08X/n",
( unsigned int )p
);
goto main_continue;
}
/*
* now sigsetjump() is OK
*/
canjump = 1;
while ( 1 )
{
/*
* 誘發SIGSEGV、SIGBUS
*/
*p = *p;
p++;
}
main_continue:
/*
* 啟動定時器
*/
init_timer( 1 );
while ( 1 )
{
/*
* 形成阻塞，降低CPU佔用率
*/
getchar();
}
return( EXIT_SUCCESS );
} /* end of main */
/************************************************************************/
--------------------------------------------------------------------------
這種技術是作業系統實現相關的。FreeBSD的si_code與標頭檔案不相符。除了FreeBSD，
其他三種OS的si_addr如願反映了棧底地址、si_pid/si_uid也能正確反映kill()訊號
源。而Solaris會出現si為NULL的情形。下面是Linux上執行示例:
[scz@ /home/scz/src]> ./siginfo_test
signo = 11
si = 0xBFFFF6B0
unused = 0xBFFFF730
si->si_signo = 11
si->si_errno = 0
si->si_code = 1
si->si_pid = 3221225472
si->si_uid = 1869479936
si->si_status = 2712942
si->si_addr = 0xC0000000 <= 棧底地址
p = 0xC0000000
signo = 14
si = 0xBFFFF5A8
unused = 0xBFFFF628
si->si_signo = 14
si->si_errno = 0
si->si_code = 128 <= SI_KERNEL 0x80 Send by kernel.
si->si_pid = 0
si->si_uid = 0
si->si_status = 896820224
si->si_addr = 0x00000000
^Z
[scz@ /home/scz/src]> bg %1
[scz@ /home/scz/src]> kill %1
signo = 15
si = 0xBFFFF5A8
unused = 0xBFFFF628
si->si_signo = 15
si->si_errno = 0
si->si_code = 0 <= SI_USER 0x00 Sent by kill, sigsend, raise.
si->si_pid = 27712 <= kill()訊號源
si->si_uid = 1000 <= kill()訊號源
si->si_status = 896820224
si->si_addr = 0x00006C40
[scz@ /home/scz/src]> echo $
27712
[scz@ /home/scz/src]> id
uid=1000(scz) gid=0(root) groups=0(root)
[scz@ /home/scz/src]>
最後結論，對於x86/FreeBSD 4.5-RELEASE，無法利用該技術分辨kill()訊號源。其
他三種作業系統可以利用該技術。
一個有趣的想法，程式分辨出kill()訊號源，反向kill訊號源。