Do not cast away const in agent_run_command

  While investigating something else, I noticed some weird code in
agent_run_command (use of memcpy rather than strcpy).  Then I noticed
that 'cmd' is used as both an in and out parameter, despite being
const.

Casting away const like this is bad.  This patch removes the const and
fixes the memcpy.  I also added a static assert to assure myself that
the code in gdbserver is correct -- gdbserver is passing its own
buffer directly to agent_run_command.
---
 gdb/linux-nat.c         |  7 ++-----
 gdbserver/server.cc     |  5 +++++
 gdbserver/tracepoint.cc |  2 +-
 gdbsupport/agent.cc     | 14 ++++++++------
 gdbsupport/agent.h      |  2 +-
 5 files changed, 17 insertions(+), 13 deletions(-)
  

Tom Tromey via Gdb-patches <gdb-patches@sourceware.org> writes:

> While investigating something else, I noticed some weird code in
> agent_run_command (use of memcpy rather than strcpy).  Then I noticed
> that 'cmd' is used as both an in and out parameter, despite being
> const.
>
> Casting away const like this is bad.  This patch removes the const and
> fixes the memcpy.  I also added a static assert to assure myself that
> the code in gdbserver is correct -- gdbserver is passing its own
> buffer directly to agent_run_command.

LGTM.

Reviewed-By: Andrew Burgess <aburgess@redhat.com>

Thanks,
Andrew

> ---
>  gdb/linux-nat.c         |  7 ++-----
>  gdbserver/server.cc     |  5 +++++
>  gdbserver/tracepoint.cc |  2 +-
>  gdbsupport/agent.cc     | 14 ++++++++------
>  gdbsupport/agent.h      |  2 +-
>  5 files changed, 17 insertions(+), 13 deletions(-)
>
> diff --git a/gdb/linux-nat.c b/gdb/linux-nat.c
> index 2b206a4ec1e..d6e69e61ef5 100644
> --- a/gdb/linux-nat.c
> +++ b/gdb/linux-nat.c
> @@ -4114,9 +4114,7 @@ linux_nat_target::static_tracepoint_markers_by_strid (const char *strid)
>    /* Pause all */
>    target_stop (ptid);
>  
> -  memcpy (s, "qTfSTM", sizeof ("qTfSTM"));
> -  s[sizeof ("qTfSTM")] = 0;
> -
> +  strcpy (s, "qTfSTM");
>    agent_run_command (pid, s, strlen (s) + 1);
>  
>    /* Unpause all.  */
> @@ -4133,8 +4131,7 @@ linux_nat_target::static_tracepoint_markers_by_strid (const char *strid)
>  	}
>        while (*p++ == ',');	/* comma-separated list */
>  
> -      memcpy (s, "qTsSTM", sizeof ("qTsSTM"));
> -      s[sizeof ("qTsSTM")] = 0;
> +      strcpy (s, "qTsSTM");
>        agent_run_command (pid, s, strlen (s) + 1);
>        p = s;
>      }
> diff --git a/gdbserver/server.cc b/gdbserver/server.cc
> index 21fb51a45d1..46dfe70838b 100644
> --- a/gdbserver/server.cc
> +++ b/gdbserver/server.cc
> @@ -51,6 +51,11 @@
>  #include "gdbsupport/scoped_restore.h"
>  #include "gdbsupport/search.h"
>  
> +/* PBUFSIZ must also be at least as big as IPA_CMD_BUF_SIZE, because
> +   the client state data is passed directly to some agent
> +   functions.  */
> +gdb_static_assert (PBUFSIZ >= IPA_CMD_BUF_SIZE);
> +
>  #define require_running_or_return(BUF)		\
>    if (!target_running ())			\
>      {						\
> diff --git a/gdbserver/tracepoint.cc b/gdbserver/tracepoint.cc
> index 37a9a8c5b7c..b59077a3896 100644
> --- a/gdbserver/tracepoint.cc
> +++ b/gdbserver/tracepoint.cc
> @@ -6820,7 +6820,7 @@ run_inferior_command (char *cmd, int len)
>    target_pause_all (false);
>    uninsert_all_breakpoints ();
>  
> -  err = agent_run_command (pid, (const char *) cmd, len);
> +  err = agent_run_command (pid, cmd, len);
>  
>    reinsert_all_breakpoints ();
>    target_unpause_all (false);
> diff --git a/gdbsupport/agent.cc b/gdbsupport/agent.cc
> index 531807be3d2..81c925dd99d 100644
> --- a/gdbsupport/agent.cc
> +++ b/gdbsupport/agent.cc
> @@ -179,14 +179,16 @@ gdb_connect_sync_socket (int pid)
>  #endif
>  }
>  
> -/* Execute an agent command in the inferior.  PID is the value of pid of the
> -   inferior.  CMD is the buffer for command.  GDB or GDBserver will store the
> -   command into it and fetch the return result from CMD.  The interaction
> -   between GDB/GDBserver and the agent is synchronized by a synchronization
> -   socket.  Return zero if success, otherwise return non-zero.  */
> +/* Execute an agent command in the inferior.  PID is the value of pid
> +   of the inferior.  CMD is the buffer for command.  It is assumed to
> +   be at least IPA_CMD_BUF_SIZE bytes long.  GDB or GDBserver will
> +   store the command into it and fetch the return result from CMD.
> +   The interaction between GDB/GDBserver and the agent is synchronized
> +   by a synchronization socket.  Return zero if success, otherwise
> +   return non-zero.  */
>  
>  int
> -agent_run_command (int pid, const char *cmd, int len)
> +agent_run_command (int pid, char *cmd, int len)
>  {
>    int fd;
>    int tid = agent_get_helper_thread_id ();
> diff --git a/gdbsupport/agent.h b/gdbsupport/agent.h
> index dceb33f6bd5..7a258e267a5 100644
> --- a/gdbsupport/agent.h
> +++ b/gdbsupport/agent.h
> @@ -22,7 +22,7 @@
>  
>  #include "gdbsupport/preprocessor.h"
>  
> -int agent_run_command (int pid, const char *cmd, int len);
> +int agent_run_command (int pid, char *cmd, int len);
>  
>  int agent_look_up_symbols (void *);
>  
> -- 
> 2.39.1