[PATCH] gdb/doc: Fix incorrect information in RSP doc

[Eli Zaretskii]

> From: Ciaran Woodward <ciaranwoodward@xmos.com>
> Cc: Ciaran Woodward <ciaranwoodward@xmos.com>
> Date: Mon, 22 Apr 2024 16:35:02 +0100
> 
> The 'PacketSize' attribute of the qSupported packet was
> documented to be the maximum size of the packet including
> the frame and checksum bytes, however this is not how it
> was treated in the code. In reality, PacketSize is the
> maximum size of the data in the RSP packets, not including
> the framing or checksum bytes.
> 
> For instance, GDB's remote.c treats it as the maximum
> number of data bytes.  See remote_read_bytes_1, where the
> size of the request is capped at PacketSize/2 (for
> hex-encoding).
> 
> Also see gdbserver's server.cc, where the internal buffer
> is sized as PBUFSIZ and PBUFSIZ-1 is used as PacketSize.
> In gdbserver's case, the buffer is not used for any of the
> framing or checksum characters. (I am not certain where the -1
> comes from. I think it comes from back when there were no
> binary packets, so packets were treated as strings with
> null terminators).
> 
> It also seems like gdbservers in the wild treat it in
> this way:
> 
> Embocosm doc:
> https://www.embecosm.com/appnotes/ean4/embecosm-howto-rsp-server-ean4-issue-2.html#id3078000
> 
> A quick glance over openocd's gdb_server.c gdb_put_packet_inner()
> function shows that the internal buffer also excludes the framing
> and checksum.
> 
> Likewise, qEmu's gdbstub.c allocates PacketSize bytes for
> the internal packet contents, and PacketSize+4 for the
> full frame.
> ---
>  gdb/doc/gdb.texinfo | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)

Thanks.  The patch is, of course, okay Texinfo-wise, but I'd like
someone who knows about the subject matter to confirm your
conclusions.

Reviewed-By: Eli Zaretskii <eliz@gnu.org>