RE: Kprobes might be stealing int3

["Mao, Bibo" <bibo.mao@intel.com>]

Anil,
I search the x86 assembly manual, about INT instruction there are three kinds:
	CC 		INT 3 		Interrupt 3―trap to debugger
	CD ib 	INT imm8 		Interrupt vector number specified by immediate byte
	CE 		INTO 		Interrupt 4―if overflow flag is 1
So like this test program, the instruction encoding will be 0x03cd, it has the same effect with 0xcc encoding. 
And currently in kprobe BREAK_INSTRUCTION is only defined as 0xcc. Maybe another encoding also need be judged.

Thanks
bibo,mao

>-----Original Message-----
>From: systemtap-owner@sourceware.org [mailto:systemtap-owner@sourceware.org]
>On Behalf Of Keshavamurthy, Anil S
>Sent: 2006年2月24日 7:34
>To: systemtap@sources.redhat.com
>Subject: FW: Kprobes might be stealing int3
>
>I went little further and found why the application is segmentation
>fault'ing.
>
>In the kprobes_handler() code, we are checking
>If (*addr != BREAK_INSTRUCTION)  and this is where the
>app is crashing since we are trying to dereference this address
>which is not a linear address.
>
>I would be happy to tryout any fix that any one provides.
>
>Thanks,
>Anil
>-----Original Message-----
>From: Keshavamurthy Anil S [mailto:anil.s.keshavamurthy@intel.com]
>Sent: Thursday, February 23, 2006 12:11 PM
>To: Systemtap
>Cc: Keshavamurthy, Anil S
>Subject: Kprobes might be stealing int3
>
>Hi,
>	I tried running the below program on both
>x86_64 and i386 and on both architecture,
>if the kernel is compiled with CONFIG_KPROBES,
>my below application segmentation faults.
>
>On kernel where CONFIG_KPROBES set to N, the
>same test program passes.
>
>Here goes the test program...
>-------------------------
>#include <stdlib.h>
>#include <signal.h>
>
>void my_trap(int sig)
>{
> printf("Test passed, all OK\n");
> exit(0);
>}
>
>int main()
>{
> signal(SIGTRAP, my_trap);
> asm volatile (".byte 0xcd,3");
> printf("Stolen interrupt, very bad!\n");
>}
>----------------------------------
>
>
>
>
>
>