Re: [PATCH v2] tracepoint: add new trace command "printf" and agent expression "printf" [0]

[Hui Zhu <teawater at gmail dot com>]

Hi guys,

Does anyone want review or reviewing this patches?

If not, I will begin to make KGTP support printk with itself.

Thanks,
Hui

On Thu, Feb 24, 2011 at 16:36, Hui Zhu <teawater@gmail.com> wrote:
> Hi guys,
>
> The prev version patches were reverted because I misunderstood the
> Tom's comments and checked in the patch.
>
> So I send a new mail for review.
>
> I add a new patch add new trace command "printf" and agent expression
> "printf" in gdb, gdbserver and doc.
>
> This printf is same with the simple gdb command, it can do formatted
> output. ?But it will happen in gdbserver part when it break by a
> tracepoint.
> Then the user can get the format value that he want in tracepint. ?It
> will be more easy and clear to handle the bug sometimes.
>
> About why I add printf to the tracepoint, I have 2 reasons:
> 1. The gdb and gdbserver connect through a low speed net. ?Sometimes,
> the debug target that I use is in the other side of the earth.
> The breakpoint commands "printf" is too slow for that issue, because
> each time the inferior is break by the breakpoint, gdbserver need send
> the rsp package to gdb, and gdb will get the data that "printf" need
> though low speed net from gdbsever. ?And sometime, it will disconnect.
> But if through tracepoint, I will not have this trouble. ?I can "set
> disconnected-tracing on" to handle the network disconnect issue. ?I
> still need to get the value from inferior through tfind and other
> commands. ?It is still be affect by the low speed network. ?So I make
> the tracepoint "printf" to handle it.
>
> 2. ?KGTP(https://code.google.com/p/kgtp/) just support the gdb
> tracepoint rsp commands. ?For not stop the Linux the Kernel. ?It
> doesn't support the breakpoint.
> So if it want directly show the Kernel val value, it need "printf".
> This printf will be very powerful that can set most part of Kernel and
> we can set condition for it.
> And in https://code.google.com/p/kgtp/wiki/HOWTO#Offline_debug, ?we
> can dump the gdbrsp package to a file and send to Kernel. ?Then kernel
> can be debug without a local gdb or a remote connect. ? But user still
> need copy the trace file to pc that have GDB. ?But if support
> tracepoint "printf", we will not need do that.
> BTW, the kgtp have supported the agent expression "printf".
>
> About the command part, I use the "printf" instead add a new commands
> because the behavior of ?this command is same with printf. They will
> use the same function string_printf(update from ui_printf) to parse
> the command arg.
>
> To support the printf command, I add a new agent expression 0x31
> printf, the format for it is:
> 0x31(op_printf) + arg(1/0) + format string with end by 0x0.
> The arg is the number of argument of printf. ?It will only be 1 (one
> argument) or 0 (no argument). ?I make it cannot have more than one
> argument because I cannot found a good way to handle va_list that send
> arguments to vprintf.
> The format string with end by 0x0 is the simple format string. ?It end
> by 0x0 then the gdbserver can use it directly.
>
> Example:
> (gdb) trace 16
> During symbol reading, DW_AT_name missing from DW_TAG_base_type.
> Tracepoint 1 at 0x4004c3: file 1.c, line 16.
> (gdb) tvariable $c
> Trace state variable $c created, with initial value 0.
> (gdb) actions
> Enter actions for tracepoint 1, one per line.
> End with a line saying just "end".
>>printf "%d 0x%lx %d\n",$c=$c+1,$rax,argc
>>end
> (gdb) target remote localhost:1234
> (gdb) tstart
> (gdb) c
>
> gdbserver/gdbserver ?localhost:1234 ./a.out
> Process ./a.out created; pid = 25804
> Listening on port 1234
> Remote debugging from host 127.0.0.1
> 1 0x7f2cb8711ec8 1
> 2 0x7f2cb8711ec8 2
> 3 0x7f2cb8711ec8 3
> 4 0x7f2cb8711ec8 4
> 5 0x7f2cb8711ec8 5
> 6 0x7f2cb8711ec8 6
> 7 0x7f2cb8711ec8 7
>
> Please help me review the patches.
>
> Thanks,
> Hui
>