[v3] remote.c: Make packet_check_result return a structure

  packet_check_result currently returns an packet_result enum.
If GDB will recieve an error in a format E.errtext, which
is possible for some q packets, such errtext is lost if
treated by packet_check_result.
Introduce a new structure which bundles enum packet_result
with possible error message or error code returned by
the GDBserver.
I plan to make more GDBserver response checking functions to use
packet_check_result to make remote.c code more consistent.
This will also allow to use E.errtext more in the future.

There's no infrastructure to test this with a test case so
I tested this by modifying store_registers_using_G function
to get an error message:

[remote] Sending packet: $GG00000000 ...

gdbserver: Wrong sized register packet (expected 1792 bytes, got 1793)
gdbserver: Invalid hex digit 71
Killing process(es): 1104002
[remote] Packet received: E01
Could not write registers; remote failure reply '01'

Reviewed-by: Thiago Jung Bauermann <thiago.bauermann@linaro.org>
---
v3: - Improve indentation

 gdb/remote.c | 148 ++++++++++++++++++++++++++++++++++++++-------------
 1 file changed, 112 insertions(+), 36 deletions(-)
  

Hi Alexandra,

I have no experience with remote, but I have a couple of styling and
other minor remarks below.

On Sun, Jan 21, 2024 at 03:50:24PM +0100, Alexandra Hájková wrote:
> packet_check_result currently returns an packet_result enum.
> If GDB will recieve an error in a format E.errtext, which
> is possible for some q packets, such errtext is lost if
> treated by packet_check_result.
> Introduce a new structure which bundles enum packet_result
> with possible error message or error code returned by
> the GDBserver.
> I plan to make more GDBserver response checking functions to use
> packet_check_result to make remote.c code more consistent.
> This will also allow to use E.errtext more in the future.
> 
> There's no infrastructure to test this with a test case so
> I tested this by modifying store_registers_using_G function
> to get an error message:
> 
> [remote] Sending packet: $GG00000000 ...
> 
> gdbserver: Wrong sized register packet (expected 1792 bytes, got 1793)
> gdbserver: Invalid hex digit 71
> Killing process(es): 1104002
> [remote] Packet received: E01
> Could not write registers; remote failure reply '01'
> 
> Reviewed-by: Thiago Jung Bauermann <thiago.bauermann@linaro.org>
> ---
> v3: - Improve indentation
> 
>  gdb/remote.c | 148 ++++++++++++++++++++++++++++++++++++++-------------
>  1 file changed, 112 insertions(+), 36 deletions(-)
> 
> diff --git a/gdb/remote.c b/gdb/remote.c
> index 72f14e28f54..8fe459a4b14 100644
> --- a/gdb/remote.c
> +++ b/gdb/remote.c
> @@ -18,8 +18,7 @@
>     along with this program.  If not, see <http://www.gnu.org/licenses/>.  */
>  
>  /* See the GDB User Guide for details of the GDB remote protocol.  */
> -
> -#include "defs.h"
> + #include "defs.h"

This looks a spurious and undesired change.

>  #include <ctype.h>
>  #include <fcntl.h>
>  #include "inferior.h"
> @@ -149,13 +148,46 @@ get_target_type_name (bool target_connected)
>  /* Analyze a packet's return value and update the packet config
>     accordingly.  */
>  
> -enum packet_result
> +enum packet_status
>  {
>    PACKET_ERROR,
>    PACKET_OK,
>    PACKET_UNKNOWN
>  };
>  
> +/* Keeps packet's return value. If packet's return value is PACKET_ERROR,
                                  ^
I think the coding standard asks for two spaces here.

> +   err_msg contains an error message string from E.string or the number
> +   stored as a string from E.num.  */
> +struct packet_result
> +{
> +  packet_result (enum packet_status status, std::string err_msg)
> +    :m_status (status), m_err_msg (std::move (err_msg))
        ^

We usually have a space between the ":" and the following token:


> +  {
> +    gdb_assert (status == PACKET_ERROR);
> +  }
> +
> +  explicit packet_result (enum packet_status status)
> +    :m_status (status)
        ^

Same here.

> +  {
> +    gdb_assert (status != PACKET_ERROR);
> +  }
> +
> +  enum packet_status status () const
> +  {
> +    return this->m_status;
> +  }
> +
> +  const char *err_msg () const
> +  {
> +    gdb_assert (this->m_status == PACKET_ERROR);
> +    return this->m_err_msg.c_str ();
> +  }
> +
> +private:
> +  enum packet_status m_status;
> +  std::string m_err_msg;
> +};
> +
>  /* Enumeration of packets for a remote target.  */
>  
>  enum {
> @@ -732,8 +764,8 @@ struct remote_features
>  
>  /* Check result value in BUF for packet WHICH_PACKET and update the packet's
>     support configuration accordingly.  */
> -  packet_result packet_ok (const char *buf, const int which_packet);
> -  packet_result packet_ok (const gdb::char_vector &buf, const int which_packet);
> +  packet_status packet_ok (const char *buf, const int which_packet);
> +  packet_status packet_ok (const gdb::char_vector &buf, const int which_packet);
>  
>    /* Configuration of a remote target's memory read packet.  */
>    memory_packet_config m_memory_read_packet_config;
> @@ -1254,7 +1286,7 @@ class remote_target : public process_stratum_target
>  					int unit_size,
>  					ULONGEST *xfered_len);
>  
> -  packet_result remote_send_printf (const char *format, ...)
> +  packet_status remote_send_printf (const char *format, ...)
>      ATTRIBUTE_PRINTF (2, 3);
>  
>    target_xfer_status remote_flash_write (ULONGEST address,
> @@ -2418,7 +2450,10 @@ add_packet_config_cmd (const unsigned int which_packet, const char *name,
>      }
>  }
>  
> -static enum packet_result
> +/* Check GDBserver's reply packet. Return packet_result
                                     ^
Missing a space here.

> +   structure which contains the packet_status enum
> +   and an error message for the PACKET_ERROR case.  */
> +static packet_result
>  packet_check_result (const char *buf)
>  {
>    if (buf[0] != '\0')
> @@ -2428,42 +2463,44 @@ packet_check_result (const char *buf)
>        if (buf[0] == 'E'
>  	  && isxdigit (buf[1]) && isxdigit (buf[2])
>  	  && buf[3] == '\0')
> +	{
>  	/* "Enn"  - definitely an error.  */
> -	return PACKET_ERROR;
> +	return { PACKET_ERROR, buf + 1 };
> +	}

The lines inside the { } block are under-intended.

>  
>        /* Always treat "E." as an error.  This will be used for
>  	 more verbose error messages, such as E.memtypes.  */
>        if (buf[0] == 'E' && buf[1] == '.')
> -	return PACKET_ERROR;
> +	return { PACKET_ERROR, buf + 2 };
>  
>        /* The packet may or may not be OK.  Just assume it is.  */
> -      return PACKET_OK;
> +      return packet_result ( PACKET_OK );
>      }
>    else
> +  {
>      /* The stub does not support the packet.  */
> -    return PACKET_UNKNOWN;
> +    return packet_result ( PACKET_UNKNOWN );
> +  }
>  }
>  
> -static enum packet_result
> +static packet_result
>  packet_check_result (const gdb::char_vector &buf)
>  {
>    return packet_check_result (buf.data ());
>  }
>  
> -packet_result
> +packet_status
>  remote_features::packet_ok (const char *buf, const int which_packet)
>  {
>    packet_config *config = &m_protocol_packets[which_packet];
>    packet_description *descr = &packets_descriptions[which_packet];
>  
> -  enum packet_result result;
> -
>    if (config->detect != AUTO_BOOLEAN_TRUE
>        && config->support == PACKET_DISABLE)
>      internal_error (_("packet_ok: attempt to use a disabled packet"));
>  
> -  result = packet_check_result (buf);
> -  switch (result)
> +  packet_result result = packet_check_result (buf);
> +  switch (result.status ())
>      {
>      case PACKET_OK:
>      case PACKET_ERROR:
> @@ -2498,10 +2535,10 @@ remote_features::packet_ok (const char *buf, const int which_packet)
>        break;
>      }
>  
> -  return result;
> +  return result.status ();
>  }
>  
> -packet_result
> +packet_status
>  remote_features::packet_ok (const gdb::char_vector &buf, const int which_packet)
>  {
>    return packet_ok (buf.data (), which_packet);
> @@ -3000,7 +3037,7 @@ remote_target::set_syscall_catchpoint (int pid, bool needed, int any_count,
>  				       gdb::array_view<const int> syscall_counts)
>  {
>    const char *catch_packet;
> -  enum packet_result result;
> +  enum packet_status result;
>    int n_sysno = 0;
>  
>    if (m_features.packet_support (PACKET_QCatchSyscalls) == PACKET_DISABLE)
> @@ -8791,9 +8828,10 @@ remote_target::send_g_packet ()
>    xsnprintf (rs->buf.data (), get_remote_packet_size (), "g");
>    putpkt (rs->buf);
>    getpkt (&rs->buf);
> -  if (packet_check_result (rs->buf) == PACKET_ERROR)
> +  packet_result result = packet_check_result (rs->buf);
> +  if (result.status () == PACKET_ERROR)
>      error (_("Could not read registers; remote failure reply '%s'"),
> -	   rs->buf.data ());
> +	   result.err_msg ());
>  
>    /* We can get out of synch in various cases.  If the first character
>       in the buffer is not a hex character, assume that has happened
> @@ -9099,9 +9137,10 @@ remote_target::store_registers_using_G (const struct regcache *regcache)
>    bin2hex (regs, p, rsa->sizeof_g_packet);
>    putpkt (rs->buf);
>    getpkt (&rs->buf);
> -  if (packet_check_result (rs->buf) == PACKET_ERROR)
> +  packet_result pkt_status = packet_check_result (rs->buf);
> +  if (pkt_status.status () == PACKET_ERROR)
>      error (_("Could not write registers; remote failure reply '%s'"),
> -	   rs->buf.data ());
> +	   pkt_status.err_msg ());
>  }
>  
>  /* Store register REGNUM, or all registers if REGNUM == -1, from the contents
> @@ -9683,7 +9722,7 @@ remote_target::remote_read_bytes (CORE_ADDR memaddr,
>     FORMAT and the remaining arguments, then gets the reply.  Returns
>     whether the packet was a success, a failure, or unknown.  */
>  
> -packet_result
> +packet_status
>  remote_target::remote_send_printf (const char *format, ...)
>  {
>    struct remote_state *rs = get_remote_state ();
> @@ -9705,8 +9744,9 @@ remote_target::remote_send_printf (const char *format, ...)
>  
>    rs->buf[0] = '\0';
>    getpkt (&rs->buf);
> +  packet_result pkt_status = packet_check_result (rs->buf);
>  
> -  return packet_check_result (rs->buf);
> +  return pkt_status.status ();

Maybe it could just be

    return packet_check_result (rs->buf).status ();

>  }
>  
>  /* Flash writing can take quite some time.  We'll set
> @@ -9718,7 +9758,7 @@ void
>  remote_target::flash_erase (ULONGEST address, LONGEST length)
>  {
>    int addr_size = gdbarch_addr_bit (current_inferior ()->arch ()) / 8;
> -  enum packet_result ret;
> +  enum packet_status ret;
>    scoped_restore restore_timeout
>      = make_scoped_restore (&remote_timeout, remote_flash_timeout);
>  
> @@ -11308,7 +11348,7 @@ remote_target::verify_memory (const gdb_byte *data, CORE_ADDR lma, ULONGEST size
>    if (target_has_execution ()
>        && m_features.packet_support (PACKET_qCRC) != PACKET_DISABLE)
>      {
> -      enum packet_result result;
> +      enum packet_status status;
>  
>        /* Make sure the remote is pointing at the right process.  */
>        set_general_process ();
> @@ -11324,10 +11364,10 @@ remote_target::verify_memory (const gdb_byte *data, CORE_ADDR lma, ULONGEST size
>  
>        getpkt (&rs->buf);
>  
> -      result = m_features.packet_ok (rs->buf, PACKET_qCRC);
> -      if (result == PACKET_ERROR)
> +      status = m_features.packet_ok (rs->buf, PACKET_qCRC);
> +      if (status == PACKET_ERROR)
>  	return -1;
> -      else if (result == PACKET_OK)
> +      else if (status == PACKET_OK)
>  	{
>  	  for (target_crc = 0, tmp = &rs->buf[1]; *tmp; tmp++)
>  	    target_crc = target_crc * 16 + fromhex (*tmp);
> @@ -12210,7 +12250,7 @@ remote_target::get_thread_local_address (ptid_t ptid, CORE_ADDR lm,
>        struct remote_state *rs = get_remote_state ();
>        char *p = rs->buf.data ();
>        char *endp = p + get_remote_packet_size ();
> -      enum packet_result result;
> +      enum packet_status result;
>  
>        strcpy (p, "qGetTLSAddr:");
>        p += strlen (p);
> @@ -12256,7 +12296,7 @@ remote_target::get_tib_address (ptid_t ptid, CORE_ADDR *addr)
>        struct remote_state *rs = get_remote_state ();
>        char *p = rs->buf.data ();
>        char *endp = p + get_remote_packet_size ();
> -      enum packet_result result;
> +      enum packet_status result;
>  
>        strcpy (p, "qGetTIBAddr:");
>        p += strlen (p);
> @@ -13821,7 +13861,7 @@ remote_target::get_trace_status (struct trace_status *ts)
>  {
>    /* Initialize it just to avoid a GCC false warning.  */
>    char *p = NULL;
> -  enum packet_result result;
> +  enum packet_status result;
>    struct remote_state *rs = get_remote_state ();
>  
>    if (m_features.packet_support (PACKET_qTStatus) == PACKET_DISABLE)
> @@ -14201,7 +14241,7 @@ remote_target::set_trace_buffer_size (LONGEST val)
>        struct remote_state *rs = get_remote_state ();
>        char *buf = rs->buf.data ();
>        char *endbuf = buf + get_remote_packet_size ();
> -      enum packet_result result;
> +      enum packet_status result;
>  
>        gdb_assert (val >= 0 || val == -1);
>        buf += xsnprintf (buf, endbuf - buf, "QTBuffer:size:");
> @@ -15527,9 +15567,10 @@ remote_target::store_memtags (CORE_ADDR address, size_t len,
>  
>    putpkt (rs->buf);
>    getpkt (&rs->buf);
> +  packet_result pkt_status = packet_check_result (rs->buf);
>  
>    /* Verify if the request was successful.  */
> -  return packet_check_result (rs->buf.data ()) == PACKET_OK;
> +  return pkt_status.status () == PACKET_OK;

Similarly, maybe it could be

    return packet_check_result (rs->buf).status () == PACKET_OK;

>  }
>  
>  /* Return true if remote target T is non-stop.  */
> @@ -15626,6 +15667,39 @@ test_memory_tagging_functions ()
>  		      expected.length ()) == 0);
>  }
>  
> +static void
> +test_packet_check_result ()
> +{
> +  std::string buf = "E01";
> +
> +  packet_result result = packet_check_result (buf.data ());
> +  SELF_CHECK (result.status () == PACKET_ERROR);
> +
> +  buf.assign("E1");
> +  result = packet_check_result (buf.data ());
> +  SELF_CHECK (result.status () == PACKET_OK);
> +
> +  buf.assign("E000");
> +  result = packet_check_result (buf.data ());
> +  SELF_CHECK (result.status () == PACKET_OK);
> +
> +  buf.assign("E.msg");
> +  result = packet_check_result (buf.data ());
> +  SELF_CHECK (result.status () == PACKET_ERROR);
> +
> +  buf.assign("E.");
> +  result = packet_check_result (buf.data ());
> +  SELF_CHECK (result.status () == PACKET_ERROR);
> +
> +  buf.assign("some response");
> +  result = packet_check_result (buf.data ());
> +  SELF_CHECK (result.status () == PACKET_OK);
> +
> +  buf.assign("");
> +  result = packet_check_result (buf.data ());
> +  SELF_CHECK (result.status () == PACKET_UNKNOWN);

For the non-PACKET_ERROR cases, it might be shorter to just write

    SELF_CHECK (packet_check_result ("E1").status () == PACKET_OK);

For the PACKET_ERROR cases, maybe also include tests checking
packet_status::err_msg () ?

Best,
Lancelot.

> +}
> +
>  } // namespace selftests
>  #endif /* GDB_SELF_TEST */
>  
> @@ -16125,5 +16199,7 @@ from the target."),
>  #if GDB_SELF_TEST
>    selftests::register_test ("remote_memory_tagging",
>  			    selftests::test_memory_tagging_functions);
> +  selftests::register_test ("packet_check_result",
> +			    selftests::test_packet_check_result);
>  #endif
>  }
> 
> -- 
> 2.43.0
>