Re: gdbstub initial code, v9

[Oleg Nesterov <oleg at redhat dot com>]

On 09/09, Frank Ch. Eigler wrote:
>
> Oleg Nesterov <oleg@redhat.com> writes:
>
> > [...]
> > But, Jan. Implementing the memory writes does not mean breakpoints
> > automatically start to work!
>
> It approximately should though.
>
> > Yes, gdb writes cc, and yes the tracee reports SIGTRAP. But after
> > that "continue" does nothing except "$c", and the tracee naturally
> > gets SIGILL. I expected that, since ugdb doesn't even know the code
> > was changed, gdb should write the original byte back before continue,
> > but this doesn't happen.
>
> In normal all-stop mode,

Currently ugdb only supports non-stop

> gdb does normally replace the old
> instruction, in order to single-step over it with the 's' packet.

Yes, probably single-stepping is needed... I am still trying to
understand how this works with gdbserver, but I see vCont:s packets.

> Perhaps you're testing some buggy non-stop aspect that only works
> with 'Z' breakpoint management packets?

No. Just a trivial test-case which printfs in a loop.

> A fuller packet trace
> would help explain.

Please see below. But the only important part is:

	$M4005ba,1:cc			<------- set bp
	$c				<------- resume

of course, this can't work.

Full trace:

	=> qSupported:multiprocess+
	<= PacketSize=400;QStartNoAckMode+;QNonStop+;multiprocess+;QPassS...
	=> QStartNoAckMode
	<= OK
	=> !
	<= OK
	=> Hgp0.0
	<= E01
	=> QNonStop:1
	<= OK
	=> qfThreadInfo
	<= E01
	=> ?
	<= OK
	=> qSymbol::
	<=
	=> vAttach;95b
	<= OK
	=> qfThreadInfo
	<= mp95b.95b
	=> qsThreadInfo
	<= l
	=> Hgp95b.95b
	<= OK
	=> vCont?
	<= vCont;t
	=> vCont;t:p95b.-1
	<= OK
	<= %Stop:T00thread:p95b.95b;
	=> vStopped
	<= OK
	=> g
	<= fcfdffffffffffff90ad5329ff7f0000ffffffffffffffff00000000000000...
	=> m600880,8
	<= 403c6d7d007f0000
	=> m7f007d6d3c48,8
	<= 00106d7d007f0000
	=> m7f007d6d1000,28
	<= 0000000000000000f6e04c7d007f0000e80760000000000080156d7d007f00...
	=> m7f007d6d1580,28
	<= 00f0ef29ff7f0000f6e04c7d007f000050f45f29ff7f000000c06c7d007f00...
	=> m7f007d4ce0f4,4
	<= 090a0069
	=> m7f007d6cc000,28
	<= 0030167d007f0000781f6d7d007f0000400b4b7d007f0000e8346d7d007f00...
	=> m7f007d6d1f78,4
	<= 2f6c6962
	=> m7f007d6d1f7c,4
	<= 2f6c6962
	=> m7f007d6d1f80,4
	<= 632e736f
	=> m7f007d6d1f84,4
	<= 2e360000
	=> m7f007d6d34e8,28
	<= 00704b7d007f00000002400000000000082e6d7d007f000000000000000000...
	=> m400200,4
	<= 2f6c6962
	=> m400204,4
	<= 2f6c642d
	=> m400208,4
	<= 6c696e75
	=> m40020c,4
	<= 782d7838
	=> m400210,4
	<= 362d3634
	=> m400214,4
	<= 2e736f2e
	=> m400218,4
	<= 32000000
	=> m7f007d6d3c40,4
	<= 01000000
	=> m7f007d6d3c48,8
	<= 00106d7d007f0000
	=> m7f007d6d3c50,8
	<= c04e4c7d007f0000
	=> Z0,7f007d4c4ec0,1
	<=
	=> m7f007d4c4ec0,1
	<= f3
	=> X7f007d4c4ec0,0:
	<=
	=> M7f007d4c4ec0,1:cc
	<= OK
	=> m600880,8
	<= 403c6d7d007f0000
	=> m7f007d6d3c48,8
	<= 00106d7d007f0000
	=> m7f007d6d1000,28
	<= 0000000000000000f6e04c7d007f0000e80760000000000080156d7d007f00...
	=> m7f007d6d1580,28
	<= 00f0ef29ff7f0000f6e04c7d007f000050f45f29ff7f000000c06c7d007f00...
	=> m7f007d4ce0f4,4
	<= 090a0069
	=> m7f007d6cc000,28
	<= 0030167d007f0000781f6d7d007f0000400b4b7d007f0000e8346d7d007f00...
	=> m7f007d6d1f78,4
	<= 2f6c6962
	=> m7f007d6d1f7c,4
	<= 2f6c6962
	=> m7f007d6d1f80,4
	<= 632e736f
	=> m7f007d6d1f84,4
	<= 2e360000
	=> m7f007d6d34e8,28
	<= 00704b7d007f00000002400000000000082e6d7d007f000000000000000000...
	=> m400200,4
	<= 2f6c6962
	=> m400204,4
	<= 2f6c642d
	=> m400208,4
	<= 6c696e75
	=> m40020c,4
	<= 782d7838
	=> m400210,4
	<= 362d3634
	=> m400214,4
	<= 2e736f2e
	=> m400218,4
	<= 32000000
	=> m7f007d6d3c40,4
	<= 01000000
	=> vCont;t:p95b.-1
	<= OK
	=> m7f007d201f40,1
	<= 48
	=> m7f007d201f40,1
	<= 48
	=> g
	<= fcfdffffffffffff90ad5329ff7f0000ffffffffffffffff00000000000000...
	=> m7f007d201f40,1
	<= 48
	=> m7f007d201f40,1
	<= 48
	=> m40056c,12
	<= 554889e5e8e3feffff89c6ba07000000bfdc
	=> m40056c,1
	<= 55
	=> m40056d,3
	<= 4889e5
	=> m40056c,12
	<= 554889e5e8e3feffff89c6ba07000000bfdc
	=> m40056c,1
	<= 55
	=> m40056d,3
	<= 4889e5
	=> m4005ba,1
	<= e8
	=> m4005ba,1
	<= e8

(gdb) b BP.c:13
Breakpoint 1 at 0x4005ba: file BP.c, line 13.

	=> M4005ba,1:cc
	<= OK

gdb writes "int 3".

(gdb) c
Continuing.

	=> QPassSignals:e;10;14;17;1a;1b;1c;21;24;25;4c;
	<= OK
	=> Hcp95b.95b
	<= OK
	=> c
	<= OK
	<= %Stop:T05thread:p95b.95b;

the tracee hits this bp and reports SIGTRAP

	=> vStopped
	<= OK
	=> g
	<= 00000000000000000006400000000000401f207d007f000000000000000000...
	=> P10=ba05400000000000
	<=
	=> G00000000000000000006400000000000401f207d007f00000000000000000...
	<=
	=> m4005ba,1
	<= cc
	=> m4005ba,1
	<= cc
	=> g
	<= 00000000000000000006400000000000401f207d007f000000000000000000...
	=> m4005bb,1
	<= 99
	=> m4005bb,1
	<= 99

Breakpoint 1, main () at BP.c:13
13                      printf("THREE %d %d\n\n", getpid(), __LINE__);
(gdb) c
Continuing.

	=> c
	<= OK

gdb just resumes the tracee,

	<= %Stop:T04thread:p95b.95b;

and of course it gets SIGILL after "int 3"

	=> vStopped
	<= OK
	=> g
	<= 00000000000000000006400000000000401f207d007f000000000000000000...
	=> m4005bc,1
	<= fe
	=> m4005bc,1
	<= fe
	=> g
	<= 00000000000000000006400000000000401f207d007f000000000000000000...
	=> m4005bc,1
	<= fe
	=> m4005bc,1
	<= fe
	=> qTStatus
	<= T0
	=> M4005ba,1:e8
	<= OK
	=> M7f007d4c4ec0,1:f3
	<= OK
	=> D;95b
	<= OK
	=> qTStatus
	<= T0