Merge forward-search/reverse-search, use gdb::def_vector, remove limit (Re: [RFA] Fix leak in forward-search)

Message ID 6e8a2a00-bcbd-cdc6-f332-f59988bb8c40@redhat.com
State New
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  • Merge forward-search/reverse-search, use gdb::def_vector, remove limit (Re: [RFA] Fix leak in forward-search)
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Commit Message

Pedro Alves Nov. 30, 2018, 7:43 p.m.
On 11/29/2018 11:05 PM, Philippe Waroquiers wrote:
> On Thu, 2018-11-29 at 15:42 +0000, Pedro Alves wrote:

>> On 11/27/2018 11:33 PM, Philippe Waroquiers wrote:


>> The patch is OK, but I think that replacing 'buf' and all that

>> manual buffer growing with a non-static gdb::def_vector<char> defined

>> outside the outer loop would be even better.

> Thanks for the review, I have pushed this version, but I have added in

> my todo list the better fix + add a test : I found no explicit

> functional test for this command + my limited time on GDB development is also

> shared with analysing the remaining several hundreds tests having a definite

> leak :).

> 


I looked a little and found that we do indeed have tests, however
they test using the "search" alias, instead of "forward-search",
which made them invisible to greps for the latter.

I also noticed a couple other things...  See the patch below.  WDYT?

From 7323b0b52c3c6cbd667904b7bb4653396ea10fac Mon Sep 17 00:00:00 2001
From: Pedro Alves <palves@redhat.com>

Date: Fri, 30 Nov 2018 18:50:23 +0000
Subject: [PATCH] Merge forward-search/reverse-search, use gdb::def_vector,
 remove limit

Back in:

 commit 85ae1317add94adef4817927e89cff80b92813dd
 Author:     Stan Shebs <shebs@codesourcery.com>
 AuthorDate: Thu Dec 8 02:27:47 1994 +0000

	     * source.c: Various cosmetic changes.
	     (forward_search_command): Handle very long source lines correctly.

a buffer with a hard limit was converted to a heap buffer:

  @@ -1228,15 +1284,26 @@ forward_search_command (regex, from_tty)
     stream = fdopen (desc, FOPEN_RT);
     clearerr (stream);
     while (1) {
  -/* FIXME!!!  We walk right off the end of buf if we get a long line!!! */
  -    char buf[4096];            /* Should be reasonable??? */
  -    register char *p = buf;
  +    static char *buf = NULL;
  +    register char *p;
  +    int cursize, newsize;
  +
  +    cursize = 256;
  +    buf = xmalloc (cursize);
  +    p = buf;

However, reverse_search_command has the exact same problem, and that
wasn't fixed.  We still have that "we walk right off" comment...

Recently, the xmalloc above was replaced with a xrealloc, because as
can be seen above, that 'buf' variable above was a static local,
otherwise we'd be leaking.  This commit replaces that and the
associated manual buffer growing with a gdb::def_vector<char>.  I
don't think there's much point in reusing the buffer across command
invocations.

While doing this, I realized that reverse_search_command is almost
identical to forward_search_command.  So this commit factors out a
common helper function instead of duplicating a lot of code.

There are some tests for "forward-search" in gdb.base/list.exp, but
since they use the "search" alias, they were a bit harder to find than
expected.  That's now fixed, both by testing both variants, and by
adding some commentary.  Also, there are no tests for the
"reverse-search" command, so this commit adds some for that too.

gdb/ChangeLog:
2018-11-30  Pedro Alves  <palves@redhat.com>

	* source.c (forward_search_command): Rename to ...
	(search_command_helper): ... this.  Add 'forward' parameter.
	Tweak to use a gdb::def_vector<char> instead of a xrealloc'ed
	buffer.  Handle backward searches too.
	(forward_search_command, reverse_search_command): Reimplement by
	calling search_command_helper.

gdb/testsuite/ChangeLog:
2018-11-30  Pedro Alves  <palves@redhat.com>

	* gdb.base/list.exp (test_forward_search): Rename to ...
	(test_forward_reverse_search): ... this.  Also test reverse-search
	and the forward-search alias.
---
 gdb/source.c                    | 149 ++++++++++++----------------------------
 gdb/testsuite/gdb.base/list.exp |  17 ++++-
 2 files changed, 59 insertions(+), 107 deletions(-)

-- 
2.14.4

Comments

Tom Tromey Nov. 30, 2018, 8:42 p.m. | #1
>>>>> "Pedro" == Pedro Alves <palves@redhat.com> writes:


Pedro>   -/* FIXME!!!  We walk right off the end of buf if we get a long line!!! */

I'm surprised all those exclamation marks didn't help us find this
sooner.  /s

Pedro> I don't think there's much point in reusing the buffer across
Pedro> command invocations.

Agreed.

Pedro> -  msg = (char *) re_comp (regex);
Pedro> +  char *msg = (char *) re_comp (regex);

Pre-existing, but I wonder why this cast is needed.  I think "const char
*msg" and removing the cast ought to be completely fine.  Or (more work)
avoid re_comp and use compiled_regex instead.

The rest seems fine to me.   Thank you for doing this.

Tom
Philippe Waroquiers Dec. 2, 2018, 4:57 p.m. | #2
On Fri, 2018-11-30 at 19:43 +0000, Pedro Alves wrote:
> I looked a little and found that we do indeed have tests, however

> they test using the "search" alias, instead of "forward-search",

> which made them invisible to greps for the latter.

> 

> I also noticed a couple other things...  See the patch below.  WDYT?

Looks much better than the previous code, and as expected, no
leaks there ...

So, FWIW, patch looks good to me ...

Philippe
Pedro Alves Dec. 8, 2018, 3:12 p.m. | #3
On 11/30/2018 08:42 PM, Tom Tromey wrote:
>>>>>> "Pedro" == Pedro Alves <palves@redhat.com> writes:

> 

> Pedro>   -/* FIXME!!!  We walk right off the end of buf if we get a long line!!! */

> 

> I'm surprised all those exclamation marks didn't help us find this

> sooner.  /s

> 

> Pedro> I don't think there's much point in reusing the buffer across

> Pedro> command invocations.

> 

> Agreed.

> 

> Pedro> -  msg = (char *) re_comp (regex);

> Pedro> +  char *msg = (char *) re_comp (regex);

> 

> Pre-existing, but I wonder why this cast is needed.  I think "const char

> *msg" and removing the cast ought to be completely fine.  


Yeah.  I did this, and pushed the patch.

> Or (more work)

> avoid re_comp and use compiled_regex instead.


I looked at this a bit, but decided not to do it, at least not in
this patch, because there are several other re_comp calls in the
tree, which made me think that it'd be better to do a pass
tweaking all the same time.  While considering that, it seems like
we end up having to pass a string as 3rd argument to compile_regex's
ctor and many different places, which makes me think that perhaps
that argument should have a default.  Similar consideration for
the compile_regex::exec method, and all arguments but the first.

Thanks,
Pedro Alves

> 

> The rest seems fine to me.   Thank you for doing this.

> 

> Tom

>

Patch

diff --git a/gdb/source.c b/gdb/source.c
index c75351e65f4..f0e98fa5d32 100644
--- a/gdb/source.c
+++ b/gdb/source.c
@@ -1521,16 +1521,14 @@  info_line_command (const char *arg, int from_tty)
 
 /* Commands to search the source file for a regexp.  */
 
+/* Helper for forward_search_command/reverse_search_command.  FORWARD
+   indicates direction: true for forward, false for
+   backward/reverse.  */
+
 static void
-forward_search_command (const char *regex, int from_tty)
+search_command_helper (const char *regex, int from_tty, bool forward)
 {
-  int c;
-  int line;
-  char *msg;
-
-  line = last_line_listed + 1;
-
-  msg = (char *) re_comp (regex);
+  char *msg = (char *) re_comp (regex);
   if (msg)
     error (("%s"), msg);
 
@@ -1544,6 +1542,10 @@  forward_search_command (const char *regex, int from_tty)
   if (current_source_symtab->line_charpos == 0)
     find_source_lines (current_source_symtab, desc.get ());
 
+  int line = (forward
+	      ? last_line_listed + 1
+	      : last_line_listed - 1);
+
   if (line < 1 || line > current_source_symtab->nlines)
     error (_("Expression not found"));
 
@@ -1553,43 +1555,35 @@  forward_search_command (const char *regex, int from_tty)
 
   gdb_file_up stream = desc.to_file (FDOPEN_MODE);
   clearerr (stream.get ());
+
+  gdb::def_vector<char> buf;
+  buf.reserve (256);
+
   while (1)
     {
-      static char *buf = NULL;
-      char *p;
-      int cursize, newsize;
-
-      cursize = 256;
-      buf = (char *) xrealloc (buf, cursize);
-      p = buf;
+      buf.resize (0);
 
-      c = fgetc (stream.get ());
+      int c = fgetc (stream.get ());
       if (c == EOF)
 	break;
       do
 	{
-	  *p++ = c;
-	  if (p - buf == cursize)
-	    {
-	      newsize = cursize + cursize / 2;
-	      buf = (char *) xrealloc (buf, newsize);
-	      p = buf + cursize;
-	      cursize = newsize;
-	    }
+	  buf.push_back (c);
 	}
       while (c != '\n' && (c = fgetc (stream.get ())) >= 0);
 
       /* Remove the \r, if any, at the end of the line, otherwise
          regular expressions that end with $ or \n won't work.  */
-      if (p - buf > 1 && p[-2] == '\r')
+      size_t sz = buf.size ();
+      if (sz >= 2 && buf[sz - 2] == '\r')
 	{
-	  p--;
-	  p[-1] = '\n';
+	  buf[sz - 2] = '\n';
+	  buf.resize (sz - 1);
 	}
 
       /* We now have a source line in buf, null terminate and match.  */
-      *p = 0;
-      if (re_exec (buf) > 0)
+      buf.push_back ('\0');
+      if (re_exec (buf.data ()) > 0)
 	{
 	  /* Match!  */
 	  print_source_lines (current_source_symtab, line, line + 1, 0);
@@ -1597,90 +1591,35 @@  forward_search_command (const char *regex, int from_tty)
 	  current_source_line = std::max (line - lines_to_list / 2, 1);
 	  return;
 	}
-      line++;
+
+      if (forward)
+	line++;
+      else
+	{
+	  line--;
+	  if (fseek (stream.get (),
+		     current_source_symtab->line_charpos[line - 1], 0) < 0)
+	    {
+	      const char *filename
+		= symtab_to_filename_for_display (current_source_symtab);
+	      perror_with_name (filename);
+	    }
+	}
     }
 
   printf_filtered (_("Expression not found\n"));
 }
 
 static void
-reverse_search_command (const char *regex, int from_tty)
+forward_search_command (const char *regex, int from_tty)
 {
-  int c;
-  int line;
-  char *msg;
-
-  line = last_line_listed - 1;
-
-  msg = (char *) re_comp (regex);
-  if (msg)
-    error (("%s"), msg);
-
-  if (current_source_symtab == 0)
-    select_source_symtab (0);
-
-  scoped_fd desc = open_source_file (current_source_symtab);
-  if (desc.get () < 0)
-    perror_with_name (symtab_to_filename_for_display (current_source_symtab));
-
-  if (current_source_symtab->line_charpos == 0)
-    find_source_lines (current_source_symtab, desc.get ());
-
-  if (line < 1 || line > current_source_symtab->nlines)
-    error (_("Expression not found"));
-
-  if (lseek (desc.get (), current_source_symtab->line_charpos[line - 1], 0)
-      < 0)
-    perror_with_name (symtab_to_filename_for_display (current_source_symtab));
-
-  gdb_file_up stream = desc.to_file (FDOPEN_MODE);
-  clearerr (stream.get ());
-  while (line > 1)
-    {
-/* FIXME!!!  We walk right off the end of buf if we get a long line!!!  */
-      char buf[4096];		/* Should be reasonable???  */
-      char *p = buf;
-
-      c = fgetc (stream.get ());
-      if (c == EOF)
-	break;
-      do
-	{
-	  *p++ = c;
-	}
-      while (c != '\n' && (c = fgetc (stream.get ())) >= 0);
-
-      /* Remove the \r, if any, at the end of the line, otherwise
-         regular expressions that end with $ or \n won't work.  */
-      if (p - buf > 1 && p[-2] == '\r')
-	{
-	  p--;
-	  p[-1] = '\n';
-	}
-
-      /* We now have a source line in buf; null terminate and match.  */
-      *p = 0;
-      if (re_exec (buf) > 0)
-	{
-	  /* Match!  */
-	  print_source_lines (current_source_symtab, line, line + 1, 0);
-	  set_internalvar_integer (lookup_internalvar ("_"), line);
-	  current_source_line = std::max (line - lines_to_list / 2, 1);
-	  return;
-	}
-      line--;
-      if (fseek (stream.get (),
-		 current_source_symtab->line_charpos[line - 1], 0) < 0)
-	{
-	  const char *filename;
-
-	  filename = symtab_to_filename_for_display (current_source_symtab);
-	  perror_with_name (filename);
-	}
-    }
+  search_command_helper (regex, from_tty, true);
+}
 
-  printf_filtered (_("Expression not found\n"));
-  return;
+static void
+reverse_search_command (const char *regex, int from_tty)
+{
+  search_command_helper (regex, from_tty, false);
 }
 
 /* If the last character of PATH is a directory separator, then strip it.  */
diff --git a/gdb/testsuite/gdb.base/list.exp b/gdb/testsuite/gdb.base/list.exp
index abfb0e165d1..9e39e51a118 100644
--- a/gdb/testsuite/gdb.base/list.exp
+++ b/gdb/testsuite/gdb.base/list.exp
@@ -485,7 +485,9 @@  proc test_list_filename_and_function {} {
 
 }
 
-proc test_forward_search {} {
+# Test the forward-search (aka search) and the reverse-search commands.
+
+proc test_forward_reverse_search {} {
 	global timeout
 
 	gdb_test_no_output "set listsize 4"
@@ -499,6 +501,17 @@  proc test_forward_search {} {
 
 	gdb_test "search 6789" "28\[ \t\]+oof .6789.;"
 
+	# Try again, we shouldn't re-find the same source line.  Also,
+	# while at it, test using the "forward-search" alias.
+	gdb_test "forward-search 6789" " not found"
+
+	# Now test backwards.  First make sure we start searching from
+	# the previous line, not the current line.
+	gdb_test "reverse-search 6789" " not found"
+
+	# Now find something in a previous line.
+	gdb_test "reverse-search 67" "26\[ \t\]+oof .67.;"
+
 	# Test that GDB won't crash if the line being searched is extremely long.
 
 	set oldtimeout $timeout
@@ -553,7 +566,7 @@  if [ set_listsize 10 ] then {
     test_repeat_list_command
     test_list_range
     test_list_filename_and_function
-    test_forward_search
+    test_forward_reverse_search
     test_only_end
     test_list_invalid_args
 }