Re: [PATCH] kprobes for 2.5.30

From: Rusty Russell (rusty@rustcorp.com.au)
Date: Tue Aug 06 2002 - 19:55:04 EST


In message <20020806164242.B22164@in.ibm.com> you write:
> - move trap1 and trap3 interrupt gates only under CONFIG_KPROBES. Please
> note that if we don't do this, we need to call restore_interrupts()
> from the dummy (post_)kprobe_handler() in include/asm-i386/kprobes.h
> when CONFIG_KPROBES is off. I didn't like this subtle side effect. hence
> the #ifdef CONFIG_KPROBES around _set_trap_gate. Still, the calling
> conventions of do_debug and do_int3 remain independent of CONFIG_KPROBES.

Hmm, I thought about this but then decided against it. Your way is
pretty subtle too: I think I prefer the restore_interrupts()
explicitly after the (failed) call to kprobe_handler, ie (on top of
your patch, which looks excellent):

diff -urpN --exclude TAGS -X /home/rusty/devel/kernel/kernel-patches/current-dontdiff --minimal working-2.5.30-kprobes-vamsi/arch/i386/kernel/traps.c working-2.5.30-kprobes/arch/i386/kernel/traps.c
--- working-2.5.30-kprobes-vamsi/arch/i386/kernel/traps.c 2002-08-07 10:45:26.000000000 +1000
+++ working-2.5.30-kprobes/arch/i386/kernel/traps.c 2002-08-07 10:51:28.000000000 +1000
@@ -517,6 +517,9 @@ asmlinkage int do_int3(struct pt_regs *r
 {
         if (kprobe_handler(regs))
                 return 1;
+ /* This is an interrupt gate, because kprobes wants interrupts
+ disabled. Normal trap handlers don't. */
+ restore_interrupts(regs);
         do_trap(3, SIGTRAP, "int3", 1, regs, error_code, NULL);
         return 0;
 }
@@ -554,6 +557,9 @@ asmlinkage int do_debug(struct pt_regs *
         if (post_kprobe_handler(regs))
                 return 1;
 
+ /* Interrupts not disabled for normal trap handling. */
+ restore_interrupts(regs);
+
         /* Mask out spurious debug traps due to lazy DR7 setting */
         if (condition & (DR_TRAP0|DR_TRAP1|DR_TRAP2|DR_TRAP3)) {
                 if (!tsk->thread.debugreg[7])
@@ -961,14 +967,9 @@ void __init trap_init(void)
 #endif
 
         set_trap_gate(0,&divide_error);
+ _set_gate(idt_table+1,14,3,&debug); /* debug trap for kprobes */
         set_intr_gate(2,&nmi);
-#ifdef CONFIG_KPROBES
- _set_gate(idt_table+1,14,3,&debug);
- _set_gate(idt_table+3,14,3,&int3);
-#else
- set_trap_gate(1,&debug);
- set_system_gate(3,&int3); /* int3-5 can be called from all */
-#endif
+ _set_gate(idt_table+3,14,3,&int3); /* int3-5 can be called from all */
         set_system_gate(4,&overflow);
         set_system_gate(5,&bounds);
         set_trap_gate(6,&invalid_op);
diff -urpN --exclude TAGS -X /home/rusty/devel/kernel/kernel-patches/current-dontdiff --minimal working-2.5.30-kprobes-vamsi/arch/i386/kernel/kprobes.c working-2.5.30-kprobes/arch/i386/kernel/kprobes.c
--- working-2.5.30-kprobes-vamsi/arch/i386/kernel/kprobes.c 2002-08-07 10:45:25.000000000 +1000
+++ working-2.5.30-kprobes/arch/i386/kernel/kprobes.c 2002-08-07 10:52:15.000000000 +1000
@@ -102,7 +102,6 @@ int kprobe_handler(struct pt_regs *regs)
 
 no_kprobe:
         preempt_enable_no_resched();
- restore_interrupts(regs);
         return ret;
 }
 
@@ -119,7 +118,7 @@ static void rearm_kprobe(struct kprobe *
 int post_kprobe_handler(struct pt_regs *regs)
 {
         if (!kprobe_running())
- goto no_kprobe;
+ return 0;
 
         if (current_kprobe->post_handler)
                 current_kprobe->post_handler(current_kprobe, regs, 0);
@@ -145,13 +144,9 @@ int post_kprobe_handler(struct pt_regs *
          * of do_debug, as if this is not a probe hit.
          */
         if (regs->eflags & TF_MASK)
- goto no_kprobe;
+ return 0;
 
         return 1;
-
-no_kprobe:
- restore_interrupts(regs);
- return 0;
 }
 
 /* Interrupts disabled, kprobe_lock held. */

--
  Anyone who quotes me in their sig is an idiot. -- Rusty Russell.
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