[PATCH v2] Make source.c:search_command_helper use source cache

[Will Hawkins <hawkinsw@obs.cr>]

The current implementation of search_command_helper accesses the line
offsets of the current program spaces's source code through
the source cache but then accesses its contents through the disk. This
PR updates the implementation so that the access of the contents is also
through the source cache.

Tested on x86_64-redhat-linux.

Signed-off-by: Will Hawkins <hawkinsw@obs.cr>
---
    v1 -> v2:
        Remove leftover debugging code.

    Rationale:
        Supporting access through the source cache during searching will make it
        easier to implement the embedded source functionality of DW_LNCT_source.

 gdb/source.c | 79 +++++++++++++++++++++++++---------------------------
 1 file changed, 38 insertions(+), 41 deletions(-)

diff --git a/gdb/source.c b/gdb/source.c
index bbeb4154258..ef042b0e96e 100644
--- a/gdb/source.c
+++ b/gdb/source.c
@@ -1617,46 +1617,45 @@ search_command_helper (const char *regex, int from_tty, bool forward)
   if (!source_open)
     error (_("source code access disabled"));
 
-  scoped_fd desc (open_source_file (loc->symtab ()));
-  if (desc.get () < 0)
-    perror_with_name (symtab_to_filename_for_display (loc->symtab ()),
-		      -desc.get ());
-
-  int line = (forward
-	      ? last_line_listed + 1
-	      : last_line_listed - 1);
-
   const std::vector<off_t> *offsets;
-  if (line < 1
-      || !g_source_cache.get_line_charpos (loc->symtab (), &offsets)
-      || line > offsets->size ())
+  if (!g_source_cache.get_line_charpos (loc->symtab (), &offsets))
     error (_("Expression not found"));
 
-  if (lseek (desc.get (), (*offsets)[line - 1], 0) < 0)
-    perror_with_name (symtab_to_filename_for_display (loc->symtab ()));
+  std::string lines;
+  if (!g_source_cache.get_source_lines (loc->symtab (), 1, offsets->size (),
+					&lines))
+    perror_with_name (symtab_to_filename_for_display (loc->symtab ()), -ENOENT);
+
+  int line_no = (forward
+		 ? last_line_listed + 1
+		 : last_line_listed - 1);
 
-  gdb_file_up stream = desc.to_file (FDOPEN_MODE);
-  clearerr (stream.get ());
+  if (line_no < 1
+      || line_no > offsets->size ())
+    error (_("Expression not found"));
+
+  size_t current_line_start = (*offsets)[line_no - 1];
 
-  gdb::def_vector<char> buf;
-  buf.reserve (256);
+  std::string buf;
 
   while (1)
     {
-      buf.resize (0);
-
-      int c = fgetc (stream.get ());
-      if (c == EOF)
+      /* Invariant: current_line_start is either the index
+	 of the start of the current line in LINES *or* the
+	 length of the source code (LINES, when there is nothing
+	 else to do).  */
+      if (current_line_start == lines.length ())
 	break;
-      do
-	{
-	  buf.push_back (c);
-	}
-      while (c != '\n' && (c = fgetc (stream.get ())) >= 0);
+
+      size_t current_line_end = ((line_no + 1) > offsets->size ()
+				 ? lines.size () - 1
+				 : (*offsets)[line_no] - 1);
+
+      size_t sz = current_line_end - current_line_start;
+      buf = lines.substr (current_line_start, sz);
 
       /* Remove the \r, if any, at the end of the line, otherwise
 	 regular expressions that end with $ or \n won't work.  */
-      size_t sz = buf.size ();
       if (sz >= 2 && buf[sz - 2] == '\r')
 	{
 	  buf[sz - 2] = '\n';
@@ -1664,29 +1663,27 @@ search_command_helper (const char *regex, int from_tty, bool forward)
 	}
 
       /* We now have a source line in buf, null terminate and match.  */
-      buf.push_back ('\0');
+      buf += '\0';
       if (re_exec (buf.data ()) > 0)
 	{
 	  /* Match!  */
-	  print_source_lines (loc->symtab (), line, line + 1, 0);
-	  set_internalvar_integer (lookup_internalvar ("_"), line);
-	  loc->set (loc->symtab (), std::max (line - lines_to_list / 2, 1));
+	  print_source_lines (loc->symtab (), line_no, line_no + 1, 0);
+	  set_internalvar_integer (lookup_internalvar ("_"), line_no);
+	  loc->set (loc->symtab (), std::max (line_no - lines_to_list / 2, 1));
 	  return;
 	}
 
       if (forward)
-	line++;
+	{
+	  line_no++;
+	  current_line_start = current_line_end + 1;
+	}
       else
 	{
-	  line--;
-	  if (line < 1)
+	  line_no--;
+	  if (line_no < 1)
 	    break;
-	  if (fseek (stream.get (), (*offsets)[line - 1], 0) < 0)
-	    {
-	      const char *filename
-		= symtab_to_filename_for_display (loc->symtab ());
-	      perror_with_name (filename);
-	    }
+	  current_line_start = (*offsets)[line_no - 1];
 	}
     }
 
-- 
2.44.0