Generate kernel panic with crash dump creating

blitzkrieg · #1 April 17th, 2012, 07:17

I try to get a little more experience in kernel debugging. How can I cause a kernel crash?
I put

Code:

dumpdev="AUTO"

and

Code:

dumpdir=/var/crash

into my rc.conf and set debug.kdb.panic to 1. There is no kernel dump in /var/crash. Then I try to use the panic() function:

Code:

#include <sys/types.h>
#include <sys/systm.h>
main() {
panic();
}

But it doesn't compile. What can I to do to crash kernel?

fluca1978 · #2 April 19th, 2012, 11:08

It does not compile because panic(9) wants a printf-like argument list.

**trasz@** · #3 April 21st, 2012, 22:11

Just do # sysctl debug.kdb.panic=1 as root.

blitzkrieg · #4 April 22nd, 2012, 06:10

Quote:

Originally Posted by trasz@

Just do # sysctl debug.kdb.panic=1 as root.

There is no crash dump in this case.

blitzkrieg · #5 April 22nd, 2012, 06:11

Quote:

Originally Posted by fluca1978

It does not compile because panic(9) wants a printf-like argument list.

I've tried with

Code:

panic("iam in panic");

It doesn't compile either.

fluca1978 · #6 April 26th, 2012, 13:19

Interesting,
I've tried to compile the same program too and I got the following:

Code:

~> uname -a
FreeBSD bsdmag 8.2-RELEASE FreeBSD 8.2-RELEASE #0: 
Fri Feb 18 02:24:46 UTC 2011     
root@almeida.cse.buffalo.edu:/usr/obj/usr/src/sys/GENERIC  i386


~> cat panic.c
#include <sys/types.h>
#include <sys/systm.h>

main() {
  panic("Hello World!");
}


~> gcc panic.c
In file included from panic.c:2:
/usr/include/sys/systm.h:239: error: expected declaration specifiers or '...' before 'uintfptr_t'
/usr/include/sys/systm.h:243: error: expected declaration specifiers or '...' before 'uintfptr_t'
In file included from panic.c:2:
/usr/include/sys/systm.h:300: error: expected '=', ',', ';', 'asm' or '__attribute__' before 'splbio'
/usr/include/sys/systm.h:301: error: expected '=', ',', ';', 'asm' or '__attribute__' before 'splcam'
/usr/include/sys/systm.h:302: error: expected '=', ',', ';', 'asm' or '__attribute__' before 'splclock'
/usr/include/sys/systm.h:303: error: expected '=', ',', ';', 'asm' or '__attribute__' before 'splhigh'
/usr/include/sys/systm.h:304: error: expected '=', ',', ';', 'asm' or '__attribute__' before 'splimp'
/usr/include/sys/systm.h:305: error: expected '=', ',', ';', 'asm' or '__attribute__' before 'splnet'
/usr/include/sys/systm.h:306: error: expected '=', ',', ';', 'asm' or '__attribute__' before 'splsoftcam'
/usr/include/sys/systm.h:307: error: expected '=', ',', ';', 'asm' or '__attribute__' before 'splsoftclock'
/usr/include/sys/systm.h:308: error: expected '=', ',', ';', 'asm' or '__attribute__' before 'splsofttty'
/usr/include/sys/systm.h:309: error: expected '=', ',', ';', 'asm' or '__attribute__' before 'splsoftvm'
/usr/include/sys/systm.h:310: error: expected '=', ',', ';', 'asm' or '__attribute__' before 'splsofttq'
/usr/include/sys/systm.h:311: error: expected '=', ',', ';', 'asm' or '__attribute__' before 'splstatclock'
/usr/include/sys/systm.h:312: error: expected '=', ',', ';', 'asm' or '__attribute__' before 'spltty'
/usr/include/sys/systm.h:313: error: expected '=', ',', ';', 'asm' or '__attribute__' before 'splvm'
/usr/include/sys/systm.h:314: error: expected ')' before 'ipl'

It seems the types defined in types.h are not processed right by the pre-processor. Is this the same error you get? Can anyone suggest a solution?

**trasz@** · #7 April 26th, 2012, 13:48

What you're trying to do - calling panic() - won't work, because panic() is a kernel routine, and you're trying to use it in a userland program. You would have to write a kernel module that calls it.

I have no idea why the panic syscall doesn't create crashdump.

fluca1978 · #8 April 26th, 2012, 15:51

Quote:

Originally Posted by trasz@

What you're trying to do - calling panic() - won't work, because panic() is a kernel routine, and you're trying to use it in a userland program. You would have to write a kernel module that calls it.

Right, the problem was that, and it was so simple.....sgrunt!

Now, for the sake of experimentation, I have written a very very simple module to test the panic system call: each time the panicBin module is unloaded the system panics.
Please do not run the module on a production system, and at least make your file systems read only!
In my system it generates correctly the crash dump, but please note that if you don't have the dumpdev option in /etc/rc.conf you will need to run savecore(8) to manually extract and store the crash out of the swap.

This is my little module code: load and the unload it to crash your system.

Code:

// panic.c

#include <sys/param.h>
#include <sys/module.h>
#include <sys/kernel.h>
#include <sys/types.h>
#include <sys/systm.h>

static int 
panicEventHandler(   
        struct module *st_module, 
        int event,                      
        void* argv                      
    )
{

        int error = 0;

        switch( event ){
                case MOD_LOAD:  
                  uprintf("\nLoading the panic module: unload to panic the system!\n");
                        break;

                case MOD_UNLOAD:  
                  uprintf("\nPanic-ing the system!!!!\n");
                  panic("Panic Module!");
                  break;

                default:
                        error = EOPNOTSUPP;     
                        break;
        }

        return error;

}



static moduledata_t panic_module = {
        "panicModule",          
        panicEventHandler,      
        NULL                    
};


DECLARE_MODULE( panicModuleBin,         
                panic_module,           
                SI_SUB_DRIVERS,
                SI_ORDER_MIDDLE
);




// Makefile
KMOD= panicBin
SRCS= panic.c

.include <bsd.kmod.mk>

blitzkrieg · #9 April 27th, 2012, 07:31

Thanks for answer.
I tried to compile your module but it doesn't compile with the following errors.

Code:

In file included from panic.c:5:
/usr/include/sys/kernel.h:373: error: expected specifier-qualifier-list before 'TAILQ_ENTRY'
In file included from panic.c:7:
/usr/include/sys/systm.h:240: error: expected declaration specifiers or '...' before 'uintfptr_t'
/usr/include/sys/systm.h:246: error: expected declaration specifiers or '...' before 'uintfptr_t'
In file included from panic.c:7:
/usr/include/sys/systm.h:312: error: expected '=', ',', ';', 'asm' or '__attribute__' before 'splbio'
/usr/include/sys/systm.h:313: error: expected '=', ',', ';', 'asm' or '__attribute__' before 'splcam'
/usr/include/sys/systm.h:314: error: expected '=', ',', ';', 'asm' or '__attribute__' before 'splclock'
/usr/include/sys/systm.h:315: error: expected '=', ',', ';', 'asm' or '__attribute__' before 'splhigh'
/usr/include/sys/systm.h:316: error: expected '=', ',', ';', 'asm' or '__attribute__' before 'splimp'
/usr/include/sys/systm.h:317: error: expected '=', ',', ';', 'asm' or '__attribute__' before 'splnet'
/usr/include/sys/systm.h:318: error: expected '=', ',', ';', 'asm' or '__attribute__' before 'splsoftcam'
/usr/include/sys/systm.h:319: error: expected '=', ',', ';', 'asm' or '__attribute__' before 'splsoftclock'
/usr/include/sys/systm.h:320: error: expected '=', ',', ';', 'asm' or '__attribute__' before 'splsofttty'
/usr/include/sys/systm.h:321: error: expected '=', ',', ';', 'asm' or '__attribute__' before 'splsoftvm'
/usr/include/sys/systm.h:322: error: expected '=', ',', ';', 'asm' or '__attribute__' before 'splsofttq'
/usr/include/sys/systm.h:323: error: expected '=', ',', ';', 'asm' or '__attribute__' before 'splstatclock'
/usr/include/sys/systm.h:324: error: expected '=', ',', ';', 'asm' or '__attribute__' before 'spltty'
/usr/include/sys/systm.h:325: error: expected '=', ',', ';', 'asm' or '__attribute__' before 'splvm'
/usr/include/sys/systm.h:326: error: expected ')' before 'ipl'
panic.c: In function 'panicEventHandler':
panic.c:30: error: 'EOPNOTSUPP' undeclared (first use in this function)
panic.c:30: error: (Each undeclared identifier is reported only once
panic.c:30: error: for each function it appears in.)
panic.c: At top level:
panic.c:51: warning: data definition has no type or storage class
panic.c:51: warning: parameter names (without types) in function declaration
panic.c:57: warning: data definition has no type or storage class
panic.c:57: error: 'panicBin' undeclared here (not in a function)
panic.c:58: error: expected ',' or ';' before 'SRCS'

fluca1978 · #10 May 3rd, 2012, 07:04

How are you compiling the module? It requires the Makefile I wrote to compile.

blitzkrieg · #11 May 4th, 2012, 06:43

Thanks for the answer. I'am newbie in compiling so I can't detect that your last post has a Makefile in it. I compiled your module and it works great.

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