Re: [PATCH] Add gdbarch_sizeof_g_packet to "struct remote_arch_state" to handle the issue that get error "Remote 'g' packet reply is too long" with qemu-system-x86_64

[Hui Zhu <teawater at gmail dot com>]

Ping.

Thanks,
Hui

On Thu, Aug 28, 2014 at 11:11 PM, Hui Zhu <teawater@gmail.com> wrote:
> If qemu-system-x86_64 start with -S, gdb will get error "Remote 'g' packet reply
> is too long", for example:
> sudo qemu-system-x86_64 -nographic -k en-us -kernel /boot/vmlinuz-3.13.0-34-generic -gdb tcp::12345 -append "console=ttyS0,115200 root=/dev/sda rw kmemleak=off" -S -m 512 -smp 1
> gdb /usr/lib/debug/boot/vmlinux-$(uname -r)
> (gdb) set debug remote 1
> (gdb) target remote :12345
> ...
> ...
> Sending packet: $g#67...Ack
> Packet received: 0000000000000000630600000000000000000000000000000000000
> 000000000f0ff00000200000000f00000000000000000000000000000000000000000000
> 000000000000000000000000000000000000000000000000000000000000000000000000
> 000000000000000000000000000000000000000000000000000000000000000000000000
> 000000000000000007f03000000000000000000000000000000000000000000000000000
> 000000000000000000000000000000000000000000000000000000000000000000000000
> 000000000000000000000000000000000000000000000000000000000000000000000000
> 000000000000000000000000000000000000000000000000000000000000000000000000
> 0000000000000000000000000000000000000000000000000801f0000
> (gdb) b start_kernel
> (gdb) c
> Continuing.
> ...
> ...
> Sending packet: $g#67...Ack
> Packet received: 0000000000000000d381ffffffff000040000000000000000010060
> 00000000000f009000000000010f4ce81ffffffff981fc081ffffffff901fc081fffffff
> f0030c1010000000000000000000000000000000000000000a869270200000000fffffff
> f0000000020000000000000002051d381ffffffffb01fc081ffffffff385bd381fffffff
> f96000000100000000000000000000000000000000000000000000000000000000000000
> 000000000000000000000000000000000000000000000000000000000000000000000000
> 000000000000000000000000000000000000000000000000000000000000000000000000
> 07f030000000000000000000000000000000000000000000000000000000000000000000
> 000000000000000000000000000000000000000000000000000000000000000000000000
> 000000000000000000000000000000000000000000000000000000000000000000000000
> 000000000000000000000000000000000000000000000000000000000000000000000000
> 000000000000000000000000000000000000000000000000000000000000000000000000
> 000000000000000000000000000000000000000000000000000000000000000000000000
> 000000000000000000000000000000000000000000000000000000000000000000000000
> 000000000000000000000000000000000000000000000000000000000000000000000000
> 0801f0000
> Remote 'g' packet reply is too long: 0000000000000000d381ffffffff0000400
> 0000000000000001006000000000000f009000000000010f4ce81ffffffff981fc081fff
> fffff901fc081ffffffff0030c1010000000000000000000000000000000000000000a86
> 9270200000000ffffffff0000000020000000000000002051d381ffffffffb01fc081fff
> fffff385bd381ffffffff960000001000000000000000000000000000000000000000000
> 000000000000000000000000000000000000000000000000000000000000000000000000
> 000000000000000000000000000000000000000000000000000000000000000000000000
> 0000000000000000000007f0300000000000000000000000000000000000000000000000
> 000000000000000000000000000000000000000000000000000000000000000000000000
> 000000000000000000000000000000000000000000000000000000000000000000000000
> 000000000000000000000000000000000000000000000000000000000000000000000000
> 000000000000000000000000000000000000000000000000000000000000000000000000
> 000000000000000000000000000000000000000000000000000000000000000000000000
> 000000000000000000000000000000000000000000000000000000000000000000000000
> 000000000000000000000000000000000000000000000000000000000000000000000000
> 000000000000000000000801f0000
> (gdb) c
> Continuing.
> Cannot execute this command while the selected thread is running.
>
> The root cause of this issue is:
> When GDB load a debug binary, function init_remote_state will be called and
> rsa->sizeof_g_packet will be initialized.
>   /* Record the maximum possible size of the g packet - it may turn out
>      to be smaller.  */
>   rsa->sizeof_g_packet = map_regcache_remote_table (gdbarch, rsa->regs);
> When remote.c get first reply of g that its size is smaller than
> rsa->sizeof_g_packet in function process_g_packet, sizeof_g_packet will be
> updated to this smaller size.
>       rsa->sizeof_g_packet = buf_len / 2;
> When inferior is breaked by breakpoint, because some reason architecture reason,
> QEMU send a packet for "g" that is more bigger than previous one.  Then GDB will
> get error in function process_g_packet.
>   /* Further sanity checks, with knowledge of the architecture.  */
>   if (buf_len > 2 * rsa->sizeof_g_packet)
>     error (_("Remote 'g' packet reply is too long: %s"), rs->buf);
>
> To handle this issue:
> This patch add "gdbarch_sizeof_g_packet" to "struct remote_arch_state", it will
> keep the size of g packet that get from gdbarch.  And function process_g_packet
> use it do the check for the reply of "g".  And update sizeof_g_packet if it is
> not same with reply of "g".
>
> 2014-08-21  Hui Zhu  <teawater@gmail.com>
>
>         * remote.c (struct remote_arch_state): Add gdbarch_sizeof_g_packet.
>         (init_remote_state): Initialize rsa->gdbarch_sizeof_g_packet.
>         (process_g_packet): Check buf_len with rsa->gdbarch_sizeof_g_packet.
>         Update code to update rsa->sizeof_g_packet if buf_len is not for it.
> ---
>  gdb/remote.c | 18 ++++++++++++------
>  1 file changed, 12 insertions(+), 6 deletions(-)
>
> diff --git a/gdb/remote.c b/gdb/remote.c
> index 357e9f2..9727915 100644
> --- a/gdb/remote.c
> +++ b/gdb/remote.c
> @@ -439,6 +439,11 @@ struct remote_arch_state
>    /* Description of the remote protocol registers.  */
>    long sizeof_g_packet;
>
> +  /* The sizeof_g_packet will be changed in some GDBstub (QEMU) when it executes.
> +     Description of the remote protocol registers that get form current
> +     gdbarch.  */
> +  long gdbarch_sizeof_g_packet;
> +
>    /* Description of the remote protocol registers indexed by REGNUM
>       (making an array gdbarch_num_regs in size).  */
>    struct packet_reg *regs;
> @@ -673,7 +678,8 @@ init_remote_state (struct gdbarch *gdbarch)
>
>    /* Record the maximum possible size of the g packet - it may turn out
>       to be smaller.  */
> -  rsa->sizeof_g_packet = map_regcache_remote_table (gdbarch, rsa->regs);
> +  rsa->gdbarch_sizeof_g_packet = map_regcache_remote_table (gdbarch, rsa->regs);
> +  rsa->sizeof_g_packet = rsa->gdbarch_sizeof_g_packet;
>
>    /* Default maximum number of characters in a packet body.  Many
>       remote stubs have a hardwired buffer size of 400 bytes
> @@ -693,8 +699,8 @@ init_remote_state (struct gdbarch *gdbarch)
>       header / footer.  NOTE: cagney/1999-10-26: I suspect that 8
>       (``$NN:G...#NN'') is a better guess, the below has been padded a
>       little.  */
> -  if (rsa->sizeof_g_packet > ((rsa->remote_packet_size - 32) / 2))
> -    rsa->remote_packet_size = (rsa->sizeof_g_packet * 2 + 32);
> +  if (rsa->gdbarch_sizeof_g_packet > ((rsa->remote_packet_size - 32) / 2))
> +    rsa->remote_packet_size = (rsa->gdbarch_sizeof_g_packet * 2 + 32);
>
>    /* Make sure that the packet buffer is plenty big enough for
>       this architecture.  */
> @@ -6070,7 +6076,7 @@ process_g_packet (struct regcache *regcache)
>    buf_len = strlen (rs->buf);
>
>    /* Further sanity checks, with knowledge of the architecture.  */
> -  if (buf_len > 2 * rsa->sizeof_g_packet)
> +  if (buf_len > 2 * rsa->gdbarch_sizeof_g_packet)
>      error (_("Remote 'g' packet reply is too long: %s"), rs->buf);
>
>    /* Save the size of the packet sent to us by the target.  It is used
> @@ -6079,11 +6085,11 @@ process_g_packet (struct regcache *regcache)
>    if (rsa->actual_register_packet_size == 0)
>      rsa->actual_register_packet_size = buf_len;
>
> -  /* If this is smaller than we guessed the 'g' packet would be,
> +  /* If this is not same with we guessed the 'g' packet would be,
>       update our records.  A 'g' reply that doesn't include a register's
>       value implies either that the register is not available, or that
>       the 'p' packet must be used.  */
> -  if (buf_len < 2 * rsa->sizeof_g_packet)
> +  if (buf_len != 2 * rsa->sizeof_g_packet)
>      {
>        rsa->sizeof_g_packet = buf_len / 2;
>
> --
> 1.9.3
>