Re: [PATCH] Exception trace for i386, mark II

Re: [PATCH] Exception trace for i386, mark II

[Arnd Bergmann]

Andi Kleen wrote:

> 
> This is a new implementation of exception trace for i386.
> 
> It adds a new exception-trace sysctl (default to off), which when enabled
> triggers printk for unhandled fault signals (SIGSEGV etc.). 

Isn't this very similar to the KERN_S390_USER_DEBUG_LOGGING sysctl?
Maybe the code can be merged, or at least they can use the same
numeric value for the sysctl.

        Arnd <><

Re: [PATCH] Exception trace for i386, mark II

[Andi Kleen]

On Sat, May 31, 2003 at 04:39:37PM +0200, Arnd Bergmann wrote:
> Andi Kleen wrote:
> 
> > 
> > This is a new implementation of exception trace for i386.
> > 
> > It adds a new exception-trace sysctl (default to off), which when enabled
> > triggers printk for unhandled fault signals (SIGSEGV etc.). 
> 
> Isn't this very similar to the KERN_S390_USER_DEBUG_LOGGING sysctl?
> Maybe the code can be merged, or at least they can use the same
> numeric value for the sysctl.

No problem from my side, although it seems a bit pointless for just 
an sysctl.  I don't think anybody expects new sysctls binary values to be stable
anymore - all the distribution kernels vary them widely.

-Andi

[PATCH] Exception trace for i386, mark II

[Andi Kleen]

This is a new implementation of exception trace for i386.

It adds a new exception-trace sysctl (default to off), which when enabled
triggers printk for unhandled fault signals (SIGSEGV etc.).  This is 
very useful to catch silent segfaults, e.g. from programs who run 
in unwritable directories and cannot coredump. It's also very useful
for running LTP. In general it gives you an early warning when something
is wrong with your system.

It won't trigger on intentional signal users who catch the signal or
when an debugger is active.  This also makes the similar facility which
has been in amd64 for a long time switchable using the sysctl. The default 
behaviour does not change.

-Andi


Index: linux/arch/i386/kernel/traps.c
===================================================================
RCS file: /home/cvs/linux-2.5/arch/i386/kernel/traps.c,v
retrieving revision 1.62
diff -u -u -r1.62 traps.c
--- linux/arch/i386/kernel/traps.c	30 May 2003 20:11:26 -0000	1.62
+++ linux/arch/i386/kernel/traps.c	31 May 2003 10:24:21 -0000
@@ -53,6 +53,8 @@
 
 #include "mach_traps.h"
 
+extern int exception_trace;
+
 asmlinkage int system_call(void);
 asmlinkage void lcall7(void);
 asmlinkage void lcall27(void);
@@ -303,6 +305,13 @@
 
 	trap_signal: {
 		struct task_struct *tsk = current;
+
+		if (exception_trace && !(tsk->flags & PT_PTRACED) && 
+		    (tsk->sighand->action[signr-1].sa.sa_handler == SIG_IGN ||
+		     (tsk->sighand->action[signr-1].sa.sa_handler == SIG_DFL)))   
+			printk(KERN_INFO "%s[%d] trap %s at eip:%lx esp:%lx err:%lx\n",
+		       tsk->comm, tsk->pid, str, regs->eip, regs->esp, error_code);
+			
 		tsk->thread.error_code = error_code;
 		tsk->thread.trap_no = trapnr;
 		if (info)
@@ -372,15 +381,22 @@
 
 asmlinkage void do_general_protection(struct pt_regs * regs, long error_code)
 {
+	struct task_struct *tsk = current;
 	if (regs->eflags & VM_MASK)
 		goto gp_in_vm86;
 
 	if (!(regs->xcs & 3))
 		goto gp_in_kernel;
 
-	current->thread.error_code = error_code;
-	current->thread.trap_no = 13;
-	force_sig(SIGSEGV, current);
+	if (exception_trace && !(tsk->flags & PT_PTRACED) && 
+	    (tsk->sighand->action[SIGSEGV-1].sa.sa_handler == SIG_IGN ||
+	     (tsk->sighand->action[SIGSEGV-1].sa.sa_handler == SIG_DFL)))
+		printk(KERN_INFO "%s[%d] gpf at eip:%lx esp:%lx err:%lx\n",
+		       tsk->comm, tsk->pid, regs->eip, regs->esp, error_code);
+	
+	tsk->thread.error_code = error_code;
+	tsk->thread.trap_no = 13;
+	force_sig(SIGSEGV, tsk);
 	return;
 
 gp_in_vm86:
Index: linux/arch/i386/mm/fault.c
===================================================================
RCS file: /home/cvs/linux-2.5/arch/i386/mm/fault.c,v
retrieving revision 1.35
diff -u -u -r1.35 fault.c
--- linux/arch/i386/mm/fault.c	30 May 2003 20:10:34 -0000	1.35
+++ linux/arch/i386/mm/fault.c	31 May 2003 10:24:21 -0000
@@ -57,6 +57,8 @@
 
 asmlinkage void do_invalid_op(struct pt_regs *, unsigned long);
 
+int exception_trace;
+
 /*
  * This routine handles page faults.  It determines the address,
  * and the problem, and then passes it off to one of the appropriate
@@ -200,6 +202,15 @@
 
 	/* User mode accesses just cause a SIGSEGV */
 	if (error_code & 4) {
+
+		if (exception_trace && !(tsk->flags & PT_PTRACED) && 
+		    (tsk->sighand->action[SIGSEGV-1].sa.sa_handler == SIG_IGN ||
+		    (tsk->sighand->action[SIGSEGV-1].sa.sa_handler == SIG_DFL)))
+			printk(KERN_INFO 
+		       "%s[%d] segfault at eip:%lx esp:%lx adr:%lx err:%lx\n",
+		       tsk->comm, tsk->pid, regs->eip, regs->esp, address, 
+		       error_code);
+
 		tsk->thread.cr2 = address;
 		tsk->thread.error_code = error_code;
 		tsk->thread.trap_no = 14;
Index: linux/include/linux/sysctl.h
===================================================================
RCS file: /home/cvs/linux-2.5/include/linux/sysctl.h,v
retrieving revision 1.52
diff -u -u -r1.52 sysctl.h
--- linux/include/linux/sysctl.h	30 May 2003 20:12:50 -0000	1.52
+++ linux/include/linux/sysctl.h	31 May 2003 10:24:25 -0000
@@ -130,6 +130,7 @@
 	KERN_PIDMAX=55,		/* int: PID # limit */
   	KERN_CORE_PATTERN=56,	/* string: pattern for core-file names */
 	KERN_PANIC_ON_OOPS=57,  /* int: whether we will panic on an oops */
+	KERN_EXCEPTION_TRACE=58, /* int: log user traps in kernel log */
 };
 
 
Index: linux/kernel/sysctl.c
===================================================================
RCS file: /home/cvs/linux-2.5/kernel/sysctl.c,v
retrieving revision 1.50
diff -u -u -r1.50 sysctl.c
--- linux/kernel/sysctl.c	30 May 2003 20:11:11 -0000	1.50
+++ linux/kernel/sysctl.c	31 May 2003 10:24:26 -0000
@@ -57,6 +57,7 @@
 extern int cad_pid;
 extern int pid_max;
 extern int sysctl_lower_zone_protection;
+extern int exception_trace;
 
 /* this is needed for the proc_dointvec_minmax for [fs_]overflow UID and GID */
 static int maxolduid = 65535;
@@ -265,6 +266,10 @@
 	 0600, NULL, &proc_dointvec},
 	{KERN_PANIC_ON_OOPS,"panic_on_oops",
 	 &panic_on_oops,sizeof(int),0644,NULL,&proc_dointvec},
+#ifdef CONFIG_X86
+	{KERN_EXCEPTION_TRACE,"exception_trace",
+	 &exception_trace,sizeof(int),0644,NULL,&proc_dointvec},
+#endif
 	{0}
 };