Fix an undefined behavior in record_line

Additionally do not completely remove symbols
at the same PC than the end marker, instead
make them non-is-stmt breakpoints.

2020-04-01  Bernd Edlinger  <bernd.edlinger@hotmail.de>

	* buildsym.c (record_line): Fix undefined behavior and preserve
	lines at eof.

1 files changed, 18 insertions, 16 deletions

diff --git a/gdb/buildsym.c b/gdb/buildsym.c
index 2d1e4419d83..46c5bb1477b 100644
--- a/gdb/buildsym.c
+++ b/gdb/buildsym.c
@@ -705,27 +705,29 @@ buildsym_compunit::record_line (struct subfile *subfile, int line,
 		      * sizeof (struct linetable_entry))));
     }
 
-  /* Normally, we treat lines as unsorted.  But the end of sequence
-     marker is special.  We sort line markers at the same PC by line
-     number, so end of sequence markers (which have line == 0) appear
-     first.  This is right if the marker ends the previous function,
-     and there is no padding before the next function.  But it is
-     wrong if the previous line was empty and we are now marking a
-     switch to a different subfile.  We must leave the end of sequence
-     marker at the end of this group of lines, not sort the empty line
-     to after the marker.  The easiest way to accomplish this is to
-     delete any empty lines from our table, if they are followed by
-     end of sequence markers.  All we lose is the ability to set
-     breakpoints at some lines which contain no instructions
-     anyway.  */
+  /* The end of sequence marker is special.  We need to reset the
+     is_stmt flag on previous lines at the same PC, otherwise these
+     lines may cause problems since they might be at the same address
+     as the following function.  For instance suppose a function calls
+     abort there is no reason to emit a ret after that point (no joke).
+     So the label may be at the same address where the following
+     function begins.  A similar problem appears if a label is at the
+     same address where an inline function ends we cannot reliably tell
+     if this is considered part of the inline function or the calling
+     program or even the next inline function, so stack traces may
+     give surprising results.  Expect gdb.cp/step-and-next-inline.exp
+     to fail if these lines are not modified here.  */
   if (line == 0 && subfile->line_vector->nitems > 0)
     {
-      e = subfile->line_vector->item + subfile->line_vector->nitems - 1;
-      while (subfile->line_vector->nitems > 0 && e->pc == pc)
+      e = subfile->line_vector->item + subfile->line_vector->nitems;
+      do
 	{
 	  e--;
-	  subfile->line_vector->nitems--;
+	  if (e->pc != pc || e->line == 0)
+	    break;
+	  e->is_stmt = 0;
 	}
+      while (e > subfile->line_vector->item);
     }
 
   e = subfile->line_vector->item + subfile->line_vector->nitems++;