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SubjectRe: [PATCH 2/5] Kprobes: Temporary disarming of reentrant probe for i386

This patch includes i386 architecture specific changes to support temporary
disarming on reentrancy of probes.

Signed-of-by: Prasanna S Panchamukhi <prasanna@in.ibm.com>

---


---

linux-2.6.12-rc4-mm2-prasanna/arch/i386/kernel/kprobes.c | 62 +++++++++++----
1 files changed, 49 insertions(+), 13 deletions(-)

diff -puN arch/i386/kernel/kprobes.c~kprobes-temporary-disarming-on-reentrancy-i386 arch/i386/kernel/kprobes.c
--- linux-2.6.12-rc4-mm2/arch/i386/kernel/kprobes.c~kprobes-temporary-disarming-on-reentrancy-i386 2005-05-24 15:28:48.000000000 +0530
+++ linux-2.6.12-rc4-mm2-prasanna/arch/i386/kernel/kprobes.c 2005-05-24 15:28:48.000000000 +0530
@@ -37,12 +37,10 @@
#include <asm/kdebug.h>
#include <asm/desc.h>

-/* kprobe_status settings */
-#define KPROBE_HIT_ACTIVE 0x00000001
-#define KPROBE_HIT_SS 0x00000002
-
static struct kprobe *current_kprobe;
static unsigned long kprobe_status, kprobe_old_eflags, kprobe_saved_eflags;
+static struct kprobe *kprobe_prev;
+static unsigned long kprobe_status_prev, kprobe_old_eflags_prev, kprobe_saved_eflags_prev;
static struct pt_regs jprobe_saved_regs;
static long *jprobe_saved_esp;
/* copy of the kernel stack at the probe fire time */
@@ -93,6 +91,31 @@ void arch_remove_kprobe(struct kprobe *p
{
}

+static inline void save_previous_kprobe(void)
+{
+ kprobe_prev = current_kprobe;
+ kprobe_status_prev = kprobe_status;
+ kprobe_old_eflags_prev = kprobe_old_eflags;
+ kprobe_saved_eflags_prev = kprobe_saved_eflags;
+}
+
+static inline void restore_previous_kprobe(void)
+{
+ current_kprobe = kprobe_prev;
+ kprobe_status = kprobe_status_prev;
+ kprobe_old_eflags = kprobe_old_eflags_prev;
+ kprobe_saved_eflags = kprobe_saved_eflags_prev;
+}
+
+static inline void set_current_kprobe(struct kprobe *p, struct pt_regs *regs)
+{
+ current_kprobe = p;
+ kprobe_saved_eflags = kprobe_old_eflags
+ = (regs->eflags & (TF_MASK | IF_MASK));
+ if (is_IF_modifier(p->opcode))
+ kprobe_saved_eflags &= ~IF_MASK;
+}
+
static inline void prepare_singlestep(struct kprobe *p, struct pt_regs *regs)
{
regs->eflags |= TF_MASK;
@@ -184,9 +207,18 @@ static int kprobe_handler(struct pt_regs
unlock_kprobes();
goto no_kprobe;
}
- arch_disarm_kprobe(p);
- regs->eip = (unsigned long)p->addr;
- ret = 1;
+ /* We have reentered the kprobe_handler(), since
+ * another probe was hit while within the handler.
+ * We here save the original kprobes variables and
+ * just single step on the instruction of the new probe
+ * without calling any user handlers.
+ */
+ save_previous_kprobe();
+ set_current_kprobe(p, regs);
+ p->nmissed++;
+ prepare_singlestep(p, regs);
+ kprobe_status = KPROBE_REENTER;
+ return 1;
} else {
p = current_kprobe;
if (p->break_handler && p->break_handler(p, regs)) {
@@ -221,11 +253,7 @@ static int kprobe_handler(struct pt_regs
}

kprobe_status = KPROBE_HIT_ACTIVE;
- current_kprobe = p;
- kprobe_saved_eflags = kprobe_old_eflags
- = (regs->eflags & (TF_MASK | IF_MASK));
- if (is_IF_modifier(p->opcode))
- kprobe_saved_eflags &= ~IF_MASK;
+ set_current_kprobe(p, regs);

if (p->pre_handler && p->pre_handler(p, regs))
/* handler has already set things up, so skip ss setup */
@@ -370,14 +398,22 @@ static inline int post_kprobe_handler(st
if (!kprobe_running())
return 0;

- if (current_kprobe->post_handler)
+ if ((kprobe_status != KPROBE_REENTER) && current_kprobe->post_handler) {
+ kprobe_status = KPROBE_HIT_SSDONE;
current_kprobe->post_handler(current_kprobe, regs, 0);
+ }

if (current_kprobe->post_handler != trampoline_post_handler)
resume_execution(current_kprobe, regs);
regs->eflags |= kprobe_saved_eflags;

+ /*Restore back the original saved kprobes variables and continue. */
+ if (kprobe_status == KPROBE_REENTER) {
+ restore_previous_kprobe();
+ goto out;
+ }
unlock_kprobes();
+out:
preempt_enable_no_resched();

/*
_
--
Have a Nice Day!

Thanks & Regards
Prasanna S Panchamukhi
Linux Technology Center
India Software Labs, IBM Bangalore
Ph: 91-80-25044636
<prasanna@in.ibm.com>
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