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.

Or I just enjoy it with myself.  :P

Thanks,
Hui

On Tue, Sep 2, 2014 at 11:26 AM, Hui Zhu <teawater@gmail.com> wrote:
> 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
>>