x86-64 had printks for user level faults for a long time. This
proved to be very useful to trace otherwise hidden faults, e.g.
on a normal kernel there is no way to see a segfault in a process
that runs in a write protected directory, even when core dumps
are enabled. Also it's useful as an early warning that something
is wrong with your system.
There was a request to port this to i386. Done with this patch.
It is turned off by default because some programs do deliberate
segfaults (e.g. lmbench), but can be enabled with a sysctl.
int 3s are not logged because they are used gdb and debugging
becomes too noisy otherwise.
As a intended side effect this also exposes the hidden exception_trace
variable that already exists in arch/x86_64 as sysctl.
Patch for 2.5.69-CVS
-Andi
Index: linux/arch/i386/kernel/traps.c
===================================================================
RCS file: /home/cvs/linux-2.5/arch/i386/kernel/traps.c,v
retrieving revision 1.54
diff -u -u -r1.54 traps.c
--- linux/arch/i386/kernel/traps.c 13 May 2003 02:56:54 -0000 1.54
+++ linux/arch/i386/kernel/traps.c 19 May 2003 18:19:33 -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 +305,11 @@
trap_signal: {
struct task_struct *tsk = current;
+
+ if (exception_trace && trapnr != 3)
+ 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 +379,20 @@
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)
+ 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 1.27
diff -u -u -r1.27 fault.c
--- linux/arch/i386/mm/fault.c 8 May 2003 05:19:20 -0000 1.27
+++ linux/arch/i386/mm/fault.c 19 May 2003 18:19:33 -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 +202,13 @@
/* User mode accesses just cause a SIGSEGV */
if (error_code & 4) {
+
+ if (exception_trace)
+ 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 1.43
diff -u -u -r1.43 sysctl.h
--- linux/include/linux/sysctl.h 12 May 2003 18:25:53 -0000 1.43
+++ linux/include/linux/sysctl.h 19 May 2003 18:19:38 -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 1.42
diff -u -u -r1.42 sysctl.c
--- linux/kernel/sysctl.c 12 May 2003 18:25:53 -0000 1.42
+++ linux/kernel/sysctl.c 19 May 2003 18:19:39 -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}
};
-
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/
This archive was generated by hypermail 2b29 : Fri May 23 2003 - 22:00:35 EST