svn commit: r333140 - head/usr.sbin/bhyve

[John Baldwin]

On Tuesday, May 01, 2018 03:17:47 PM John Baldwin wrote:
> Author: jhb
> Date: Tue May  1 15:17:46 2018
> New Revision: 333140
> URL: https://svnweb.freebsd.org/changeset/base/333140
> 
> Log:
>   Initial debug server for bhyve.

This is definitely "early" work and there are still many things to improve.
Note that if you aren't using a file gdb you will need to explicitly set
the architecture.  Here is an example of booting a VM with -G w1234 which
stops at the first instruction:

(gdb) set architecture i386:x86-64
The target architecture is assumed to be i386:x86-64
(gdb) target remote localhost:1234
Remote debugging using localhost:1234
warning: No executable has been specified and target does not support
determining executable automatically.  Try using the "file" command.
0xffffffff8029e9a0 in ?? ()
(gdb) x/i $pc
=> 0xffffffff8029e9a0:  movw   $0x1234,0x472
(gdb) si
0xffffffff8029e9aa in ?? ()
(gdb) info threads
  Id   Target Id         Frame 
* 1    Thread 1 (vCPU 0) 0xffffffff8029e9aa in ?? ()
(gdb) c
Continuing.
^C[New Thread 2]

Thread 1 received signal SIGTRAP, Trace/breakpoint trap.
0xffffffff807e0673 in ?? ()
(gdb) info threads
  Id   Target Id         Frame 
* 1    Thread 1 (vCPU 0) 0xffffffff807e0673 in ?? ()
  2    Thread 2 (vCPU 1) 0xffffffff807f4fa2 in ?? ()
(gdb) info registers 
rax            0x0      0
rbx            0xffffffff80d75400       -2133371904
rcx            0x0      0
rdx            0x40024  262180
rsi            0x1      1
rdi            0xffffffffffffffff       -1
rbp            0xfffffe0015282980       0xfffffe0015282980
rsp            0xfffffe0015282970       0xfffffe0015282970
r8             0xfffff80002148000       -8796058124288
r9             0xffffffff80d49090       -2133553008
r10            0xfffff80002148000       -8796058124288
r11            0x1      1
r12            0x0      0
r13            0xfffff80002144000       -8796058140672
r14            0xffffffffffffffff       -1
r15            0xffffffff80c30a00       -2134701568
rip            0xffffffff807e0673       0xffffffff807e0673
eflags         0x246    [ PF ZF IF ]
cs             0x20     32
ss             0x28     40
ds             0x3b     59
es             0x3b     59
fs             0x13     19
gs             0x28     40
fs_base        <unavailable>
gs_base        <unavailable>
(gdb) detach
Detaching from program: , Remote target
Ending remote debugging.

Stepping will only work on Intel CPUs currently and not AMD.  (Implementing
single-stepping on AMD will prove "interesting" as it will mean raising
single-step debug exceptions in the guest and then hiding them from the
guest as well as properly shadowing the TF flag in %rflags in the guest and
injecting suitable DB# exceptions in the guest if it is also tracing itself,
etc.)

There is a lot more to work on, but I think this is a useful initial
checkpoint.

Note that just as with the debug server in QEMU, kgdb does not currently
know how to enumerate kernel threads on top of the virtual CPU "threads",
so commands like 'tid' and 'proc' will not work if using kgdb.

-- 
John Baldwin