[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
Doug Evans
xdje42@gmail.com
Mon Nov 17 07:23:00 GMT 2014
On Sun, Nov 16, 2014 at 11:08 PM, Hui Zhu <teawater@gmail.com> wrote:
> 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
>>>
Hi.
When I've used qemu and seen this issue, it's because the inferior has
stopped with the current arch different than what gdb thinks.
E.g., if I boot linux on qemu and then Ctrl-C, then when qemu talks to
gdb it either presents a 32bit or a 64bit arch to gdb, depending on
what program qemu was currently running (the kernel may be 64 bit but
the kernel can be running a mix of 32bit and 64bit programs).
Thus gdb is being presented, randomly, with 32bit or 64bit arches over
the same remote connection, which obviously isn't going to work.
So I guess my first question is, is this patch just a bandaid?
IOW, the problem here is more than just packet size, isn't it?
GDB currently doesn't support debugging of i386 and amd64 arches over
one remote debug connection.
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