Re: [PATCH v2 1/3] kgdb: Add kgdb_mem2ebin function for converting memory to binary format

[Daniel Thompson <danielt@kernel.org>]

On Wed, Dec 11, 2024 at 07:39:53AM -0800, Amal Raj T wrote:
> From: Amal Raj T <amalrajt@meta.com>
>
> Add a new function kgdb_mem2ebin that converts memory
> to binary format, escaping special characters
> ('$', '#', and '}').

What about the '*' character?

The gdb docs say "Responses sent by the stub must also escape 0x2a
(ASCII ‘*’), so that it is not interpreted as the start of a run-length
encoded sequence".


> kgdb_mem2ebin function ensures
> that memory data is properly formatted and escaped
> before being sent over the wire. Additionally, this
> function reduces the amount of data exchanged between
> debugger compared to hex.
>
> Signed-off-by: Amal Raj T <amalrajt@meta.com>
> ---
>  include/linux/kgdb.h   |  1 +
>  kernel/debug/gdbstub.c | 31 +++++++++++++++++++++++++++++++
>  2 files changed, 32 insertions(+)
>
> diff --git a/include/linux/kgdb.h b/include/linux/kgdb.h
> index 76e891ee9e37..fa3cf38a14de 100644
> --- a/include/linux/kgdb.h
> +++ b/include/linux/kgdb.h
> @@ -322,6 +322,7 @@ extern struct kgdb_io *dbg_io_ops;
>
>  extern int kgdb_hex2long(char **ptr, unsigned long *long_val);
>  extern char *kgdb_mem2hex(char *mem, char *buf, int count);
> +extern char *kgdb_mem2ebin(char *mem, char *buf, int count);
>  extern int kgdb_hex2mem(char *buf, char *mem, int count);
>
>  extern int kgdb_isremovedbreak(unsigned long addr);
> diff --git a/kernel/debug/gdbstub.c b/kernel/debug/gdbstub.c
> index f625172d4b67..6198d2eb49c4 100644
> --- a/kernel/debug/gdbstub.c
> +++ b/kernel/debug/gdbstub.c
> @@ -257,6 +257,37 @@ char *kgdb_mem2hex(char *mem, char *buf, int count)
>  	return buf;
>  }
>
> +/*
> + * Convert memory to binary format for GDB remote protocol
> + * transmission, escaping special characters ($, #, and }).
> + */

It would be good to include a link to the following in this comment:
https://sourceware.org/gdb/current/onlinedocs/gdb.html/Overview.html#Binary-Data

Doug already mentioned putting buffer size expectations in this comment.
Maybe also mention that the worst case packing is identical to
kgdb_mem2hex() (e.g. 2*count + 1).


Daniel.