From 8f54c55ea44f1906c23b5f01aea92b548b1e8839 Mon Sep 17 00:00:00 2001
From: Gregory LEOCADIE <gregory.leocadie@datadoghq.com>
Date: Thu, 8 Dec 2022 11:54:29 +0100
Subject: Fix bug + add test

---
 src/mi/backtrace.c          | 20 ++++++++++++---
 tests/Gtest-trace.c         | 59 +++++++++++++++++++++++++++++++++++++++++++++
 tests/check-namespace.sh.in |  1 +
 3 files changed, 77 insertions(+), 3 deletions(-)

diff --git a/src/mi/backtrace.c b/src/mi/backtrace.c
index 00e4de8d..8fea3444 100644
--- a/src/mi/backtrace.c
+++ b/src/mi/backtrace.c
@@ -92,14 +92,28 @@ unw_backtrace2 (void **buffer, int size, unw_context_t* uc2)
   if (unlikely (unw_init_local2 (&cursor, &uc, UNW_INIT_SIGNAL_FRAME) < 0))
     return 0;
 
-  int n = size;
+  // get the first ip from the context
+  unw_word_t ip;
+
+  if (unw_get_reg (&cursor, UNW_REG_IP, &ip) < 0)
+    return 0;
 
+  buffer[0] =  (void *) (uintptr_t)ip;
+
+  // update buffer info to collect the rest of the IPs
+  buffer = buffer+1;
+  int remaining_size = size-1;
+
+  int n = remaining_size;
+
+  // returns the number of frames collected by tdep_trace or slow_backtrace
+  // and add 1 to it (the one we retrieved above)
   if (unlikely (tdep_trace (&cursor, buffer, &n) < 0))
     {
-      return slow_backtrace (buffer, size, &uc, UNW_INIT_SIGNAL_FRAME);
+      return slow_backtrace (buffer, remaining_size, &uc, UNW_INIT_SIGNAL_FRAME) + 1;
     }
 
-  return n;
+  return n + 1;
 }
 
 #ifdef CONFIG_WEAK_BACKTRACE
diff --git a/tests/Gtest-trace.c b/tests/Gtest-trace.c
index fa207fca..e0a5d64d 100644
--- a/tests/Gtest-trace.c
+++ b/tests/Gtest-trace.c
@@ -139,6 +139,64 @@ do_backtrace (void)
 	}
 }
 
+void
+do_backtrace_with_context(void *context)
+{
+  unw_word_t ip;
+  int ret = -UNW_ENOINFO;
+  int depth = 0;
+  int i, m;
+
+  if (verbose)
+    printf ("\tnormal trace:\n");
+
+  if (unw_init_local2 (&cursor, (unw_context_t*)context, UNW_INIT_SIGNAL_FRAME) < 0)
+    panic ("unw_init_local2 failed!\n");
+
+  do
+    {
+      unw_get_reg (&cursor, UNW_REG_IP, &ip);
+      addresses[0][depth] = (void *) ip;
+    }
+  while ((ret = unw_step (&cursor)) > 0 && ++depth < 128);
+
+  if (ret < 0)
+    {
+      unw_get_reg (&cursor, UNW_REG_IP, &ip);
+      printf ("FAILURE: unw_step() returned %d for ip=%lx\n", ret, (long) ip);
+      ++num_errors;
+    }
+
+  if (verbose)
+    for (i = 0; i < depth; ++i)
+      printf ("\t #%-3d ip=%p\n", i, addresses[0][i]);
+
+  if (verbose)
+    printf ("\n\tvia unw_backtrace2():\n");
+
+  m = unw_backtrace2 (addresses[1], 128, (unw_context_t*)context);
+
+  if (verbose)
+    for (i = 0; i < m; ++i)
+	printf ("\t #%-3d ip=%p\n", i, addresses[1][i]);
+
+  if (m != depth+1)
+    {
+      printf ("FAILURE: unw_step() loop and unw_backtrace2() depths differ: %d vs. %d\n", depth, m);
+      ++num_errors;
+    }
+
+  if (m == depth + 1)
+    for (i = 0; i < depth; ++i)
+      /* Allow one in difference in comparison, trace returns adjusted addresses. */
+      if (labs((unw_word_t) addresses[0][i] - (unw_word_t) addresses[1][i]) > 1)
+	{
+          printf ("FAILURE: unw_step() loop and uwn_backtrace2() addresses differ at %d: %p vs. %p\n",
+                  i, addresses[0][i], addresses[1][i]);
+          ++num_errors;
+	}
+}
+
 void
 foo (long val UNUSED)
 {
@@ -222,6 +280,7 @@ sighandler (int signal, void *siginfo UNUSED, void *context)
       printf ("\n");
     }
   do_backtrace();
+  do_backtrace_with_context(context);
 }
 
 int
diff --git a/tests/check-namespace.sh.in b/tests/check-namespace.sh.in
index 656e3818..a1b28a7b 100644
--- a/tests/check-namespace.sh.in
+++ b/tests/check-namespace.sh.in
@@ -137,6 +137,7 @@ check_local_unw_abi () {
 
     match unw_backtrace
     @CONFIG_WEAK_BACKTRACE_TRUE@match backtrace
+    match unw_backtrace2
 
     case ${plat} in
 	arm)
-- 
cgit v1.2.1