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Subject[patch] x86_64 specific function return probes
The following patch adds the x86_64 architecture specific implementation
for function return probes to the 2.6.12-rc5-mm2 kernel.

--rusty

arch/x86_64/kernel/kprobes.c | 98 ++++++++++++++++++++++++++++++++++++++++++-
arch/x86_64/kernel/process.c | 16 +++++++
include/asm-x86_64/kprobes.h | 3 +
3 files changed, 116 insertions(+), 1 deletion(-)

Index: linux-2.6.12-rc5-mm2/arch/x86_64/kernel/kprobes.c
===================================================================
--- linux-2.6.12-rc5-mm2.orig/arch/x86_64/kernel/kprobes.c
+++ linux-2.6.12-rc5-mm2/arch/x86_64/kernel/kprobes.c
@@ -27,6 +27,8 @@
* <prasanna@in.ibm.com> adapted for x86_64
* 2005-Mar Roland McGrath <roland@redhat.com>
* Fixed to handle %rip-relative addressing mode correctly.
+ * 2005-May Rusty Lynch <rusty.lynch@intel.com>
+ * Added function return probes functionality
*/

#include <linux/config.h>
@@ -272,6 +274,50 @@ static void prepare_singlestep(struct kp
regs->rip = (unsigned long)p->ainsn.insn;
}

+struct task_struct *arch_get_kprobe_task(void *ptr)
+{
+ return ((struct thread_info *) (((unsigned long) ptr) &
+ (~(THREAD_SIZE -1))))->task;
+}
+
+void arch_prepare_kretprobe(struct kretprobe *rp, struct pt_regs *regs)
+{
+ unsigned long *sara = (unsigned long *)regs->rsp;
+ struct kretprobe_instance *ri;
+ static void *orig_ret_addr;
+
+ /*
+ * Save the return address when the return probe hits
+ * the first time, and use it to populate the (krprobe
+ * instance)->ret_addr for subsequent return probes at
+ * the same addrress since stack address would have
+ * the kretprobe_trampoline by then.
+ */
+ if (((void*) *sara) != kretprobe_trampoline)
+ orig_ret_addr = (void*) *sara;
+
+ if ((ri = get_free_rp_inst(rp)) != NULL) {
+ ri->rp = rp;
+ ri->stack_addr = sara;
+ ri->ret_addr = orig_ret_addr;
+ add_rp_inst(ri);
+ /* Replace the return addr with trampoline addr */
+ *sara = (unsigned long) &kretprobe_trampoline;
+ } else {
+ rp->nmissed++;
+ }
+}
+
+void arch_kprobe_flush_task(struct task_struct *tk)
+{
+ struct kretprobe_instance *ri;
+ while ((ri = get_rp_inst_tsk(tk)) != NULL) {
+ *((unsigned long *)(ri->stack_addr)) =
+ (unsigned long) ri->ret_addr;
+ recycle_rp_inst(ri);
+ }
+}
+
/*
* Interrupts are disabled on entry as trap3 is an interrupt gate and they
* remain disabled thorough out this function.
@@ -366,6 +412,55 @@ no_kprobe:
}

/*
+ * For function-return probes, init_kprobes() establishes a probepoint
+ * here. When a retprobed function returns, this probe is hit and
+ * trampoline_probe_handler() runs, calling the kretprobe's handler.
+ */
+ void kretprobe_trampoline_holder(void)
+ {
+ asm volatile ( ".global kretprobe_trampoline\n"
+ "kretprobe_trampoline: \n"
+ "nop\n");
+ }
+
+/*
+ * Called when we hit the probe point at kretprobe_trampoline
+ */
+int trampoline_probe_handler(struct kprobe *p, struct pt_regs *regs)
+{
+ struct task_struct *tsk;
+ struct kretprobe_instance *ri;
+ struct hlist_head *head;
+ struct hlist_node *node;
+ unsigned long *sara = (unsigned long *)regs->rsp - 1;
+
+ tsk = arch_get_kprobe_task(sara);
+ head = kretprobe_inst_table_head(tsk);
+
+ hlist_for_each_entry(ri, node, head, hlist) {
+ if (ri->stack_addr == sara && ri->rp) {
+ if (ri->rp->handler)
+ ri->rp->handler(ri, regs);
+ }
+ }
+ return 0;
+}
+
+void trampoline_post_handler(struct kprobe *p, struct pt_regs *regs,
+ unsigned long flags)
+{
+ struct kretprobe_instance *ri;
+ /* RA already popped */
+ unsigned long *sara = ((unsigned long *)regs->rsp) - 1;
+
+ while ((ri = get_rp_inst(sara))) {
+ regs->rip = (unsigned long)ri->ret_addr;
+ recycle_rp_inst(ri);
+ }
+ regs->eflags &= ~TF_MASK;
+}
+
+/*
* Called after single-stepping. p->addr is the address of the
* instruction whose first byte has been replaced by the "int 3"
* instruction. To avoid the SMP problems that can occur when we
@@ -455,7 +550,8 @@ int post_kprobe_handler(struct pt_regs *
current_kprobe->post_handler(current_kprobe, regs, 0);
}

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

/*Restore back the original saved kprobes variables and continue. */
Index: linux-2.6.12-rc5-mm2/include/asm-x86_64/kprobes.h
===================================================================
--- linux-2.6.12-rc5-mm2.orig/include/asm-x86_64/kprobes.h
+++ linux-2.6.12-rc5-mm2/include/asm-x86_64/kprobes.h
@@ -38,6 +38,9 @@ typedef u8 kprobe_opcode_t;
: (((unsigned long)current_thread_info()) + THREAD_SIZE - (ADDR)))

#define JPROBE_ENTRY(pentry) (kprobe_opcode_t *)pentry
+#define ARCH_SUPPORTS_KRETPROBES
+
+void kretprobe_trampoline(void);

/* Architecture specific copy of original instruction*/
struct arch_specific_insn {
Index: linux-2.6.12-rc5-mm2/arch/x86_64/kernel/process.c
===================================================================
--- linux-2.6.12-rc5-mm2.orig/arch/x86_64/kernel/process.c
+++ linux-2.6.12-rc5-mm2/arch/x86_64/kernel/process.c
@@ -35,6 +35,7 @@
#include <linux/utsname.h>
#include <linux/perfctr.h>
#include <linux/random.h>
+#include <linux/kprobes.h>

#include <asm/uaccess.h>
#include <asm/pgtable.h>
@@ -294,6 +295,14 @@ void exit_thread(void)
{
struct task_struct *me = current;
struct thread_struct *t = &me->thread;
+
+ /*
+ * Remove function-return probe instances associated with this task
+ * and put them back on the free list. Do not insert an exit probe for
+ * this function, it will be disabled by kprobe_flush_task if you do.
+ */
+ kprobe_flush_task(me);
+
if (me->thread.io_bitmap_ptr) {
struct tss_struct *tss = &per_cpu(init_tss, get_cpu());

@@ -314,6 +323,13 @@ void flush_thread(void)
struct task_struct *tsk = current;
struct thread_info *t = current_thread_info();

+ /*
+ * Remove function-return probe instances associated with this task
+ * and put them back on the free list. Do not insert an exit probe for
+ * this function, it will be disabled by kprobe_flush_task if you do.
+ */
+ kprobe_flush_task(tsk);
+
if (t->flags & _TIF_ABI_PENDING)
t->flags ^= (_TIF_ABI_PENDING | _TIF_IA32);

-
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