The following is a patch provided by Ananth Mavinakayanahalli that implements the new PPC64 specific parts of the new function return probe design. Changes include: * Addition of kretprobe_trampoline to act as a dummy function for instrumented functions to return to, and for the return probe infrastructure to place a kprobe on on, gaining control so that the return probe handler can be called, and so that the instruction pointer can be moved back to the original return address. * Addition of arch_init(), allowing a kprobe to be registered on kretprobe_trampoline * Addition of trampoline_probe_handler() which is used as the pre_handler for the kprobe inserted on kretprobe_implementation. This is the function that handles the details for calling the return probe handler function and returning control back at the original return address * Addition of arch_prepare_kretprobe() which is setup as the pre_handler for a kprobe registered at the beginning of the target function by kernel/kprobes.c so that a return probe instance can be setup when a caller enters the target function. (A return probe instance contains all the needed information for trampoline_probe_handler to do it's job.) * Hooks added to the exit path of a task so that we can cleanup any left-over return probe instances (i.e. if a task dies while inside a targeted function then the return probe instance was reserved at the beginning of the function but the function never returns so we need to mark the instance as unused.) --rusty signed-off-by: Ananth N Mavinakayanahali signed-off-by: Rusty Lynch arch/ppc64/kernel/kprobes.c | 99 ++++++++++++++++++++++++++++++++++++++++++++ arch/ppc64/kernel/process.c | 4 + include/asm-ppc64/kprobes.h | 3 + 3 files changed, 106 insertions(+) Index: linux-2.6.12-mm1/arch/ppc64/kernel/kprobes.c =================================================================== --- linux-2.6.12-mm1.orig/arch/ppc64/kernel/kprobes.c +++ linux-2.6.12-mm1/arch/ppc64/kernel/kprobes.c @@ -105,6 +105,23 @@ static inline void restore_previous_kpro kprobe_saved_msr = kprobe_saved_msr_prev; } +void arch_prepare_kretprobe(struct kretprobe *rp, struct pt_regs *regs) +{ + struct kretprobe_instance *ri; + + if ((ri = get_free_rp_inst(rp)) != NULL) { + ri->rp = rp; + ri->task = current; + ri->ret_addr = (kprobe_opcode_t *)regs->link; + + /* Replace the return addr with trampoline addr */ + regs->link = (unsigned long)kretprobe_trampoline; + add_rp_inst(ri); + } else { + rp->nmissed++; + } +} + static inline int kprobe_handler(struct pt_regs *regs) { struct kprobe *p; @@ -195,6 +212,78 @@ no_kprobe: } /* + * Function return probe trampoline: + * - init_kprobes() establishes a probepoint here + * - When the probed function returns, this probe + * causes the handlers to fire + */ +void kretprobe_trampoline_holder(void) +{ + asm volatile(".global kretprobe_trampoline\n" + "kretprobe_trampoline:\n" + "nop\n"); +} + +/* + * Called when the probe at kretprobe trampoline is hit + */ +int trampoline_probe_handler(struct kprobe *p, struct pt_regs *regs) +{ + struct kretprobe_instance *ri = NULL; + struct hlist_head *head; + struct hlist_node *node, *tmp; + unsigned long orig_ret_address = 0; + unsigned long trampoline_address =(unsigned long)&kretprobe_trampoline; + + head = kretprobe_inst_table_head(current); + + /* + * It is possible to have multiple instances associated with a given + * task either because an multiple functions in the call path + * have a return probe installed on them, and/or more then one return + * return probe was registered for a target function. + * + * We can handle this because: + * - instances are always inserted at the head of the list + * - when multiple return probes are registered for the same + * function, the first instance's ret_addr will point to the + * real return address, and all the rest will point to + * kretprobe_trampoline + */ + hlist_for_each_entry_safe(ri, node, tmp, head, hlist) { + if (ri->task != current) + /* another task is sharing our hash bucket */ + continue; + + if (ri->rp && ri->rp->handler) + ri->rp->handler(ri, regs); + + orig_ret_address = (unsigned long)ri->ret_addr; + recycle_rp_inst(ri); + + if (orig_ret_address != trampoline_address) + /* + * This is the real return address. Any other + * instances associated with this task are for + * other calls deeper on the call stack + */ + break; + } + + BUG_ON(!orig_ret_address || (orig_ret_address == trampoline_address)); + regs->nip = orig_ret_address; + + unlock_kprobes(); + + /* + * By returning a non-zero value, we are telling + * kprobe_handler() that we have handled unlocking + * and re-enabling preemption. + */ + return 1; +} + +/* * Called after single-stepping. p->addr is the address of the * instruction whose first byte has been replaced by the "breakpoint" * instruction. To avoid the SMP problems that can occur when we @@ -331,3 +420,13 @@ int longjmp_break_handler(struct kprobe memcpy(regs, &jprobe_saved_regs, sizeof(struct pt_regs)); return 1; } + +static struct kprobe trampoline_p = { + .addr = (kprobe_opcode_t *) &kretprobe_trampoline, + .pre_handler = trampoline_probe_handler +}; + +int __init arch_init(void) +{ + return register_kprobe(&trampoline_p); +} Index: linux-2.6.12-mm1/arch/ppc64/kernel/process.c =================================================================== --- linux-2.6.12-mm1.orig/arch/ppc64/kernel/process.c +++ linux-2.6.12-mm1/arch/ppc64/kernel/process.c @@ -37,6 +37,7 @@ #include #include #include +#include #include #include @@ -310,6 +311,8 @@ void show_regs(struct pt_regs * regs) void exit_thread(void) { + kprobe_flush_task(current); + #ifndef CONFIG_SMP if (last_task_used_math == current) last_task_used_math = NULL; @@ -325,6 +328,7 @@ void flush_thread(void) { struct thread_info *t = current_thread_info(); + kprobe_flush_task(current); if (t->flags & _TIF_ABI_PENDING) t->flags ^= (_TIF_ABI_PENDING | _TIF_32BIT); Index: linux-2.6.12-mm1/include/asm-ppc64/kprobes.h =================================================================== --- linux-2.6.12-mm1.orig/include/asm-ppc64/kprobes.h +++ linux-2.6.12-mm1/include/asm-ppc64/kprobes.h @@ -42,6 +42,9 @@ typedef unsigned int kprobe_opcode_t; #define JPROBE_ENTRY(pentry) (kprobe_opcode_t *)((func_descr_t *)pentry) +#define ARCH_SUPPORTS_KRETPROBES +void kretprobe_trampoline(void); + /* Architecture specific copy of original instruction */ struct arch_specific_insn { /* copy of original instruction */ --