Re: [PATCH RESEND] gdb: remove static buffer in command_line_input

[Simon Marchi <simon.marchi@polymtl.ca>]

On 12/16/22 08:21, Pedro Alves wrote:
> On 2022-12-15 7:06 p.m., Simon Marchi via Gdb-patches wrote:
>>    else
>>      {
>>        /* Copy whole line including terminating null, and we're
>>  	 done.  */
>> -      buffer_grow (cmd_line_buffer, rl, len + 1);
>> -      cmd = cmd_line_buffer->buffer;
>> +      cmd_line_buffer.append (rl, len + 1);
>> +      return true;
> 
> std::string is guaranteed to be null terminated, but, it can also hold
> \0 characters in the middle of the string.  Isn't that
> 
>   cmd_line_buffer.append (rl, len + 1);
> 
> ending up with an embedded \0 at the end of the string, with cmd_line_buffer.size() accounting for it?

Argh, yes!  I rewrote this patch from scratch multiple times until I got
something satisfactory, and I know I changed that in a previous
iteration, because I remember having that thought.

Here's a patch to fix it:


From 8757d2ec9edf2ae0b77039ca0ecc9ca32fd87256 Mon Sep 17 00:00:00 2001
From: Simon Marchi <simon.marchi@polymtl.ca>
Date: Fri, 16 Dec 2022 08:34:56 -0500
Subject: [PATCH] gdb: don't copy final null character in
 command_line_append_input_line

The modified std::string::append call currently copies the null
character from the source string, leaving the std::string with a null
character in its content, part of its size, in addition to the null
character managed by the std::string itself  We don't want to copy that
null character, so remove that "+ 1".

Change-Id: I412fe9bd6b08e7ce7604ef5d8038b62f1a784c9b
---
 gdb/event-top.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/gdb/event-top.c b/gdb/event-top.c
index fa86a89e4a19..fa9e1f3f6a73 100644
--- a/gdb/event-top.c
+++ b/gdb/event-top.c
@@ -640,7 +640,7 @@ command_line_append_input_line (std::string &cmd_line_buffer, const char *rl)
     {
       /* Copy whole line including terminating null, and we're
 	 done.  */
-      cmd_line_buffer.append (rl, len + 1);
+      cmd_line_buffer.append (rl, len);
       return true;
     }
 }

base-commit: e60a615dde5d6674a6488b74afe807a775551407
-- 
2.38.1