[PATCH] binutils: improve holes detection in .debug_loclists.

[PATCH] binutils: improve holes detection in .debug_loclists.

[Clément Chigot]

The previous warnings about holes in .debug_loclists sections don't
take into account the headers of each CU and could include the locviews
if they precede the loclist.

The following warning can be triggered between two CU.
    ... <previous CU views> ...
    0000001d <End of list>

    0000002a v000000000000000 v000000000000000 location view pair
    0000002c v000000000000000 v000000000000000 location view pair

readelf: Warning: There is a hole [0x1e - 0x2e] in .debug_loclists section.
    0000002e v000000000000000 v000000000000000 views at 0000002a for:
    ...

But [0x1e - 0x2a] corresponds to the CU header and  [0x2a - 0x2e] are
the locviews.  Thus there is no hole here.

binutils/ChangeLog:

	* dwarf.c (display_debug_loc): Adjust holes detections for
	headers and locviews.
---
 binutils/dwarf.c | 47 +++++++++++++++++++++++++++++++++--------------
 1 file changed, 33 insertions(+), 14 deletions(-)

diff --git a/binutils/dwarf.c b/binutils/dwarf.c
index 404a0bdbac6..ffe3c10ff75 100644
--- a/binutils/dwarf.c
+++ b/binutils/dwarf.c
@@ -7158,7 +7158,7 @@ display_debug_loc (struct dwarf_section *section, void *file)
   const char *suffix = strrchr (section->name, '.');
   bool is_dwo = false;
   int is_loclists = strstr (section->name, "debug_loclists") != NULL;
-  uint64_t expected_start = 0;
+  uint64_t header_size = 0;
 
   if (suffix && strcmp (suffix, ".dwo") == 0)
     is_dwo = true;
@@ -7209,7 +7209,7 @@ display_debug_loc (struct dwarf_section *section, void *file)
       if (offset_entry_count != 0)
 	return display_offset_entry_loclists (section);
 
-      expected_start = hdrptr - section_begin;
+      header_size = hdrptr - section_begin;
     }
 
   if (load_debug_info (file) == 0)
@@ -7265,12 +7265,12 @@ display_debug_loc (struct dwarf_section *section, void *file)
     error (_("No location lists in .debug_info section!\n"));
 
   if (debug_information [first].num_loc_offsets > 0
-      && debug_information [first].loc_offsets [0] != expected_start
-      && debug_information [first].loc_views [0] != expected_start)
+      && debug_information [first].loc_offsets [0] != header_size
+      && debug_information [first].loc_views [0] != header_size)
     warn (_("Location lists in %s section start at %#" PRIx64
 	    " rather than %#" PRIx64 "\n"),
 	  section->name, debug_information [first].loc_offsets [0],
-	  expected_start);
+	  header_size);
 
   if (!locs_sorted)
     array = (unsigned int *) xcmalloc (num_loc_list, sizeof (unsigned int));
@@ -7282,10 +7282,9 @@ display_debug_loc (struct dwarf_section *section, void *file)
 
   printf (_("    Offset   Begin            End              Expression\n"));
 
-  seen_first_offset = 0;
   for (i = first; i < num_debug_info_entries; i++)
     {
-      uint64_t offset, voffset;
+      uint64_t offset = 0, voffset = 0;
       uint64_t base_address;
       unsigned int k;
       int has_frame_base;
@@ -7300,6 +7299,24 @@ display_debug_loc (struct dwarf_section *section, void *file)
 		 sizeof (*array), loc_offsets_compar);
 	}
 
+      /* .debug_loclists has a per-unit header.
+	 Update start if we are detecting it.  */
+      if (debug_information [i].dwarf_version == 5)
+	{
+	  j = locs_sorted ? 0 : array [0];
+
+	  if (debug_information [i].num_loc_offsets)
+	    offset = debug_information [i].loc_offsets [j];
+
+	  if (debug_information [i].num_loc_views)
+	    voffset = debug_information [i].loc_views [j];
+
+	  /* Assume that the size of the header is constant across CUs. */
+	  if (((start - section_begin) + header_size == offset)
+	      || ((start -section_begin) + header_size == voffset))
+	    start += header_size;
+	}
+
       int adjacent_view_loclists = 1;
       for (k = 0; k < debug_information [i].num_loc_offsets; k++)
 	{
@@ -7330,19 +7347,21 @@ display_debug_loc (struct dwarf_section *section, void *file)
 		start = vstart;
 	    }
 
-	  if (!seen_first_offset || !adjacent_view_loclists)
-	    seen_first_offset = 1;
-	  else
+	  if (start < next)
 	    {
-	      if (start < next)
+	      if (vnext && vnext < next)
 		warn (_("There is a hole [%#tx - %#" PRIx64 "]"
 			" in %s section.\n"),
-		      start - section_begin, offset, section->name);
-	      else if (start > next)
-		warn (_("There is an overlap [%#tx - %#" PRIx64 "]"
+		      start - section_begin, voffset, section->name);
+	      else
+		warn (_("There is a hole [%#tx - %#" PRIx64 "]"
 			" in %s section.\n"),
 		      start - section_begin, offset, section->name);
 	    }
+	  else if (start > next)
+	    warn (_("There is an overlap [%#tx - %#" PRIx64 "]"
+		    " in %s section.\n"),
+		  start - section_begin, offset, section->name);
 	  start = next;
 	  vstart = vnext;
 
-- 
2.25.1

Re: [PATCH] binutils: improve holes detection in .debug_loclists.

[Nick Clifton]

Hi Clément,

> binutils/ChangeLog:
> 
> 	* dwarf.c (display_debug_loc): Adjust holes detections for
> 	headers and locviews.

Approved - please apply.

Cheers
   Nick