[PATCH v3 2/4] libdw: Refactor dwarf_next_lines and fix skipped CU

[Omar Sandoval]

From: Omar Sandoval <osandov@fb.com>

dwarf_next_lines has two loops over CUs: one from the CU after the given
CU to the end, and one from the first CU up to _but not including_ the
given CU.  This means that the given CU is never checked.

This is unlikely to matter in practice since CUs usually correspond 1:1
with line number tables in the same order, but let's fix it anyways.
Refactoring it to one loop fixes the problem and simplifies the next
change to support DWARF package files.

	* libdw/dwarf_next_lines.c (dwarf_next_lines): Refactor loops
	over CUs into one loop.

Signed-off-by: Omar Sandoval <osandov@fb.com>
---
 libdw/dwarf_next_lines.c | 75 +++++++++++++++++-----------------------
 1 file changed, 31 insertions(+), 44 deletions(-)

diff --git a/libdw/dwarf_next_lines.c b/libdw/dwarf_next_lines.c
index 74854ecd..6a9fe361 100644
--- a/libdw/dwarf_next_lines.c
+++ b/libdw/dwarf_next_lines.c
@@ -95,62 +95,49 @@ dwarf_next_lines (Dwarf *dbg, Dwarf_Off off,
     {
       /* We need to find the matching CU to get the comp_dir.  Use the
 	 given CU as hint where to start searching.  Normally it will
-	 be the next CU that has a statement list. */
+	 be the next CU that has a statement list.  If the CUs are in a
+	 different order from the line tables, then we do a linear
+	 search.  */
       Dwarf_CU *given_cu = *cu;
       Dwarf_CU *next_cu = given_cu;
-      bool found = false;
-      while (INTUSE(dwarf_get_units) (dbg, next_cu, &next_cu, NULL, NULL,
-				      &cudie, NULL) == 0)
+      bool restarted = false;
+      while (1)
 	{
+	  if (restarted && next_cu == given_cu)
+	    {
+	      /* We checked all of the CUs and there was no match.  */
+	      *cu = NULL;
+	      break;
+	    }
+	  if (INTUSE(dwarf_get_units) (dbg, next_cu, &next_cu, NULL, NULL,
+				       &cudie, NULL) != 0)
+	    {
+	      /* We didn't find the matching CU after the starting point.
+	         Check the CUs up to the starting point.  */
+	      next_cu = NULL;
+	      restarted = true;
+	      continue;
+	    }
+
+	  Dwarf_Word stmt_off = 0;
 	  if (dwarf_hasattr (&cudie, DW_AT_stmt_list))
 	    {
 	      Dwarf_Attribute attr;
-	      Dwarf_Word stmt_off;
 	      if (dwarf_formudata (dwarf_attr (&cudie, DW_AT_stmt_list, &attr),
-				   &stmt_off) == 0
-		  && stmt_off == off)
-		{
-		  found = true;
-		  break;
-		}
+				   &stmt_off) != 0)
+		continue;
 	    }
-	  else if (off == 0
-		   && (next_cu->unit_type == DW_UT_split_compile
-		       || next_cu->unit_type == DW_UT_split_type))
+	  /* Split units have an implicit offset of 0.  */
+	  else if (next_cu->unit_type != DW_UT_split_compile
+		   && next_cu->unit_type != DW_UT_split_type)
+	    continue;
+
+	  if (stmt_off == off)
 	    {
-	      /* For split units (in .dwo files) there is only one table
-		 at offset zero (containing just the files, no lines).  */
-	      found = true;
+	      *cu = next_cu;
 	      break;
 	    }
 	}
-
-      if (!found && given_cu != NULL)
-	{
-	  /* The CUs might be in a different order from the line
-	     tables. Need to do a linear search (but stop at the given
-	     CU, since we already searched those.  */
-	  next_cu = NULL;
-	  while (INTUSE(dwarf_get_units) (dbg, next_cu, &next_cu, NULL, NULL,
-					  &cudie, NULL) == 0
-		 && next_cu != given_cu)
-	    {
-	      Dwarf_Attribute attr;
-	      Dwarf_Word stmt_off;
-	      if (dwarf_formudata (dwarf_attr (&cudie, DW_AT_stmt_list, &attr),
-				   &stmt_off) == 0
-		  && stmt_off == off)
-		{
-		  found = true;
-		  break;
-		}
-	    }
-	}
-
-      if (found)
-	*cu = next_cu;
-      else
-	*cu = NULL;
     }
   else
     *cu = NULL;
-- 
2.43.2