bz6436 backtraces from uprobes

This implements proper unwinding from uprobes in the presence of
uretprobe trampolines.

* runtime/stack.c (_stp_stack_print): Rework for uprobe context case
  and refactor a bit.
* runtime/uprobes2/uprobes.h (GET_PC_URETPROBE_NONE): new constant
* runtime/uprobes2/uprobes.c (uprobe_get_pc): Support translating the
  trampoline function from uprobe context in addition to uretprobe
  context.
* runtime/uprobes/uprobes.h (GET_PC_URETPROBE_NONE): ditto
* runtime/uprobes/uprobes.c (uprobe_get_pc): ditto
* tapsets.cxx (uprobe_derived_probe_group::emit_module_decls):
  Initialize ri in context to GET_PC_URETPROBE_NONE in generated
  enter_uprobe_probe.
* testsuite/systemtap.context/fib.stp: Add an option to do a backtrace
  on function entry.
* testsuite/systemtap.context/fib.exp: Test backtrace in function
  entry (uprobe) probes.

8 files changed, 117 insertions, 69 deletions

diff --git a/runtime/stack.c b/runtime/stack.c
index 50dde6e1..612fa010 100644
--- a/runtime/stack.c
+++ b/runtime/stack.c
@@ -132,25 +132,29 @@ static void _stp_stack_print(struct pt_regs *regs, int verbose, struct kretprobe
 				_stp_print("\nReturning to  : ");
 			}
 			_stp_symbol_print((unsigned long)_stp_ret_addr_r(pi));
-                } else if (ri) {
-#ifdef CONFIG_UTRACE /* as a proxy for presence of uprobes */
+			_stp_print_char('\n');
+#ifdef CONFIG_UTRACE /* as a proxy for presence of uprobes... */
+                } else if (ri && ri != GET_PC_URETPROBE_NONE) {
 			if (verbose == SYM_VERBOSE_FULL) {
 				_stp_print("Returning from: ");
-				_stp_usymbol_print(ri->rp->u.vaddr, tsk);  /* otherwise this dereference fails */
+				/* ... otherwise this dereference fails */
+				_stp_usymbol_print(ri->rp->u.vaddr, tsk);
 				_stp_print("\nReturning to  : ");
 				_stp_usymbol_print(ri->ret_addr, tsk);
+				_stp_print_char('\n');				
 			} else
 				_stp_func_print(ri->ret_addr, verbose, 0, tsk);
 #endif
+		} else if (verbose == SYM_VERBOSE_BRIEF) {
+			_stp_func_print(REG_IP(regs), verbose, 0, tsk);
 		} else {
 			_stp_print_char(' ');
 			if (tsk)
-			  _stp_usymbol_print(REG_IP(regs), tsk);
+				_stp_usymbol_print(REG_IP(regs), tsk);
 			else
-			  _stp_symbol_print(REG_IP(regs));
-		}
-		if (verbose != SYM_VERBOSE_BRIEF)
+				_stp_symbol_print(REG_IP(regs));
 			_stp_print_char('\n');
+		}
 	} else if (pi)
 		_stp_printf("%p %p ", (int64_t)(long)_stp_ret_addr_r(pi), (int64_t) REG_IP(regs));
 	else 
diff --git a/runtime/uprobes/uprobes.c b/runtime/uprobes/uprobes.c
index cdb98707..5ccc7102 100644
--- a/runtime/uprobes/uprobes.c
+++ b/runtime/uprobes/uprobes.c
@@ -2599,37 +2599,46 @@ static void uretprobe_set_trampoline(struct uprobe_process *uproc,
 unsigned long uprobe_get_pc(struct uretprobe_instance *ri, unsigned long pc,
 			unsigned long sp)
 {
-        struct uretprobe *rp;
-        struct uprobe_kimg *uk;
-        struct uprobe_process *uproc;
-        unsigned long trampoline_addr;
-        struct hlist_node *r;
-        struct uretprobe_instance *ret_inst;
-
-        if (!ri)
-                return 0;
-        rp = ri->rp;
-        uk = (struct uprobe_kimg *)rp->u.kdata;
-        if (!uk)
-                return 0;
-        uproc = uk->ppt->uproc;
-        if (IS_ERR(uproc->uretprobe_trampoline_addr))
-          return pc;
-        trampoline_addr = (unsigned long)uproc->uretprobe_trampoline_addr;
-        if (pc != trampoline_addr)
-                return pc;
-        r = &ri->hlist;
-        hlist_for_each_entry_from(ret_inst, r, hlist) {
-                if (ret_inst->ret_addr == trampoline_addr)
-                        continue;
-                /* First handler with a stack pointer lower than the
-                   address (or equal) must be the one. */
-                if (ret_inst->sp == sp || compare_stack_ptrs(ret_inst->sp, sp))
-                        return ret_inst->ret_addr;
-        }
-        printk(KERN_ERR "Original return address for trampoline not found at "
-               "0x%lx pid/tgid=%d/%d\n", sp, current->pid, current->tgid);
-        return 0;
+	struct uretprobe *rp;
+	struct uprobe_kimg *uk;
+	struct uprobe_task *utask;
+	struct uprobe_process *uproc;
+	unsigned long trampoline_addr;
+	struct hlist_node *r;
+	struct uretprobe_instance *ret_inst;
+
+	if (!ri)
+		return 0;
+	if (ri == GET_PC_URETPROBE_NONE) {
+		utask = uprobe_find_utask(current);
+		if (!utask)
+			return 0;
+		uproc = utask->uproc;
+		r = utask->uretprobe_instances.first;
+	} else {
+		rp = ri->rp;
+		uk = (struct uprobe_kimg *)rp->u.kdata;
+		if (!uk)
+			return 0;
+		uproc = uk->ppt->uproc;
+		r = &ri->hlist;		
+	}
+	if (IS_ERR(uproc->uretprobe_trampoline_addr))
+	  return pc;
+	trampoline_addr = (unsigned long)uproc->uretprobe_trampoline_addr;
+	if (pc != trampoline_addr)
+		return pc;
+	hlist_for_each_entry_from(ret_inst, r, hlist) {
+		if (ret_inst->ret_addr == trampoline_addr)
+			continue;
+		/* First handler with a stack pointer lower than the
+		   address (or equal) must be the one. */
+		if (ret_inst->sp == sp || compare_stack_ptrs(ret_inst->sp, sp))
+			return ret_inst->ret_addr;
+	}
+	printk(KERN_ERR "Original return address for trampoline not found at "
+	       "0x%lx pid/tgid=%d/%d\n", sp, current->pid, current->tgid);
+	return 0;
 }
 
 EXPORT_SYMBOL_GPL(uprobe_get_pc);
diff --git a/runtime/uprobes/uprobes.h b/runtime/uprobes/uprobes.h
index e888f9e8..80725f23 100644
--- a/runtime/uprobes/uprobes.h
+++ b/runtime/uprobes/uprobes.h
@@ -99,7 +99,11 @@ extern void unmap_uretprobe(struct uretprobe *rp);
  * Given a program counter, translate it back to the original address
  * if it is the address of the trampoline. sp is the stack pointer for
  * the frame that corresponds to the address.
+ *
+ * When not called from a uretprobe hander, pass GET_PC_URETPROBE_NONE
+ * instead of a uretprobe_instance.
  */
+#define GET_PC_URETPROBE_NONE ((struct uretprobe_instance *)-1L)
 extern unsigned long uprobe_get_pc(struct uretprobe_instance *ri,
                                    unsigned long pc,
                                    unsigned long sp);
diff --git a/runtime/uprobes2/uprobes.c b/runtime/uprobes2/uprobes.c
index 02941e26..623855ff 100644
--- a/runtime/uprobes2/uprobes.c
+++ b/runtime/uprobes2/uprobes.c
@@ -2840,37 +2840,46 @@ static void uretprobe_set_trampoline(struct uprobe_process *uproc,
 unsigned long uprobe_get_pc(struct uretprobe_instance *ri, unsigned long pc,
 			unsigned long sp)
 {
-        struct uretprobe *rp;
-        struct uprobe_kimg *uk;
-        struct uprobe_process *uproc;
-        unsigned long trampoline_addr;
-        struct hlist_node *r;
-        struct uretprobe_instance *ret_inst;
-
-        if (!ri)
-                return 0;
-        rp = ri->rp;
-        uk = (struct uprobe_kimg *)rp->u.kdata;
-        if (!uk)
-                return 0;
-        uproc = uk->ppt->uproc;
-        if (IS_ERR(uproc->uretprobe_trampoline_addr))
-          return pc;
-        trampoline_addr = (unsigned long)uproc->uretprobe_trampoline_addr;
-        if (pc != trampoline_addr)
-                return pc;
-        r = &ri->hlist;
-        hlist_for_each_entry_from(ret_inst, r, hlist) {
-                if (ret_inst->ret_addr == trampoline_addr)
-                        continue;
-                /* First handler with a stack pointer lower than the
-                   address (or equal) must be the one. */
-                if (ret_inst->sp == sp || compare_stack_ptrs(ret_inst->sp, sp))
-                        return ret_inst->ret_addr;
-        }
-        printk(KERN_ERR "Original return address for trampoline not found at "
-               "0x%lx pid/tgid=%d/%d\n", sp, current->pid, current->tgid);
-        return 0;
+	struct uretprobe *rp;
+	struct uprobe_kimg *uk;
+	struct uprobe_task *utask;
+	struct uprobe_process *uproc;
+	unsigned long trampoline_addr;
+	struct hlist_node *r;
+	struct uretprobe_instance *ret_inst;
+
+	if (!ri)
+		return 0;
+	if (ri == GET_PC_URETPROBE_NONE) {
+		utask = uprobe_find_utask(current);
+		if (!utask)
+			return 0;
+		uproc = utask->uproc;
+		r = utask->uretprobe_instances.first;
+	} else {
+		rp = ri->rp;
+		uk = (struct uprobe_kimg *)rp->u.kdata;
+		if (!uk)
+			return 0;
+		uproc = uk->ppt->uproc;
+		r = &ri->hlist;		
+	}
+	if (IS_ERR(uproc->uretprobe_trampoline_addr))
+	  return pc;
+	trampoline_addr = (unsigned long)uproc->uretprobe_trampoline_addr;
+	if (pc != trampoline_addr)
+		return pc;
+	hlist_for_each_entry_from(ret_inst, r, hlist) {
+		if (ret_inst->ret_addr == trampoline_addr)
+			continue;
+		/* First handler with a stack pointer lower than the
+		   address (or equal) must be the one. */
+		if (ret_inst->sp == sp || compare_stack_ptrs(ret_inst->sp, sp))
+			return ret_inst->ret_addr;
+	}
+	printk(KERN_ERR "Original return address for trampoline not found at "
+	       "0x%lx pid/tgid=%d/%d\n", sp, current->pid, current->tgid);
+	return 0;
 }
 
 EXPORT_SYMBOL_GPL(uprobe_get_pc);
diff --git a/runtime/uprobes2/uprobes.h b/runtime/uprobes2/uprobes.h
index 5d2a826e..c4e1f59c 100644
--- a/runtime/uprobes2/uprobes.h
+++ b/runtime/uprobes2/uprobes.h
@@ -92,7 +92,11 @@ extern void unmap_uretprobe(struct uretprobe *rp);
  * Given a program counter, translate it back to the original address
  * if it is the address of the trampoline. sp is the stack pointer for
  * the frame that corresponds to the address.
+ *
+ * When not called from a uretprobe hander, pass GET_PC_URETPROBE_NONE
+ * instead of a uretprobe_instance.
  */
+#define GET_PC_URETPROBE_NONE ((struct uretprobe_instance *)-1L)
 extern unsigned long uprobe_get_pc(struct uretprobe_instance *ri,
                                    unsigned long pc,
                                    unsigned long sp);
diff --git a/tapsets.cxx b/tapsets.cxx
index bac47761..0936eacd 100644
--- a/tapsets.cxx
+++ b/tapsets.cxx
@@ -4735,6 +4735,7 @@ uprobe_derived_probe_group::emit_module_decls (systemtap_session& s)
   s.op->newline() << "if (sup->spec_index < 0 ||"
                   << "sup->spec_index >= " << probes.size() << ") return;"; // XXX: should not happen
   s.op->newline() << "c->regs = regs;";
+  s.op->newline() << "c->ri = GET_PC_URETPROBE_NONE;";
 
   // Make it look like the IP is set as it would in the actual user
   // task when calling real probe handler. Reset IP regs on return, so
diff --git a/testsuite/systemtap.context/fib.exp b/testsuite/systemtap.context/fib.exp
index cc4d75a1..5026e5d0 100644
--- a/testsuite/systemtap.context/fib.exp
+++ b/testsuite/systemtap.context/fib.exp
@@ -35,3 +35,17 @@ expect {
 }
 wait
 if {$fibcalls == 18 && $maincalls == 2} { pass "$test ($fibcalls $maincalls)" } { fail "$test ($fibcalls $maincalls)" }
+
+spawn stap -c "$testexe 10" -- $teststp --entry
+set fibcalls 0
+set maincalls 0
+expect {
+    -timeout 120
+    -re {^fib[^\r\n]*[\r\n]} { incr fibcalls; exp_continue }
+    -re {^main[^\r\n]*[\r\n]} { incr maincalls; exp_continue }
+    -re {^[^\r\n]*[\r\n]} {exp_continue}
+    timeout { fail "$test (timeout)" }
+    eof { }
+}
+wait
+if {$fibcalls == 55 && $maincalls == 10} { pass "$test ($fibcalls $maincalls)" } { fail "$test ($fibcalls $maincalls)" }
diff --git a/testsuite/systemtap.context/fib.stp b/testsuite/systemtap.context/fib.stp
index 85c2fc1d..fe2415f5 100644
--- a/testsuite/systemtap.context/fib.stp
+++ b/testsuite/systemtap.context/fib.stp
@@ -5,13 +5,16 @@ probe process("fib").function("fib").call {
     depth++
     if (depth > max_depth) {
             max_depth = depth
+            %( $# > 0 %? print_ubacktrace_brief(); printf("\n") %)
     }
 }
 
 probe process("fib").function("fib").return {
+    %( $# == 0 %?
     if (depth == max_depth) {
             print_ubacktrace_brief()
             printf("\n")
     }
+    %)
     depth--
 }