qemu-system-sparc64: entering the debugger
mark.cave-ayland at ilande.co.uk
Tue Apr 12 12:51:54 UTC 2016
On 12/04/16 10:06, Mark Cave-Ayland wrote:
>> So it looks like something has already gone wrong simply trying to dump
>> the process map. Fortunately the number of QEMU translation blocks
>> between the output of the "ps/m" header and the "KDB reentering" is
>> quite small so I've uploaded it to
>> Can anyone have a quick look at the link above and give me an idea as to
>> roughly what the code is doing here?
It seems that if you boot directly into ddb and use ps/m then you end up
with a NULL pointer dereference:
FreeBSD/sparc64 bootstrap loader, Revision 1.0
(mca at freebsd, Thu Sep 24 00:27:19 BST 2015)
bootpath="/pci at 1fe,0/pci-ata at 5/ide1 at 8200/cdrom at 0:a"
/boot/kernel/kernel data=0xd893c0+0x20ffd8 syms=[0x8+0xdc578+0x8+0xcb349]
Hit [Enter] to boot immediately, or any other key for command prompt.
Booting [/boot/kernel/kernel] in 9 seconds...
Type '?' for a list of commands, 'help' for more detailed help.
OK boot -d
jumping to kernel entry at 0xc00b0000.
GDB: no debug ports present
KDB: debugger backends: ddb
KDB: current backend: ddb
KDB: enter: Boot flags requested debugger
[ thread pid 0 tid 0 ]
Stopped at 0xc0630b00
pid ppid pgrp uid state wmesg wchan cmd
0 0 0 0KDB: reentering
KDB: stack backtrace:
(null)() at 0xc063105c
(null)() at 0xc09e193c
(null)() at 0xc00b1078
(null)() at 0xc011bb1c
The NULL pointer reference occurs here:
0x00000000c0122008: ldx [ %l2 + 0x3d8 ], %g1 ! %g1 = 0
0x00000000c012200c: ldx [ %g1 + 0x18 ], %g1 !
0x00000000c0122010: brz,pn %g1, 0xc0122050
AFAICT the corresponding part of db_ps.c is this:
if (p->p_session != NULL && SESS_LEADER(p))
strlcat(state, "s", sizeof(state));
Here p->p_session expands to p->p_pgrp->pg_session which gives us the
exception because p->p_pgrp is set to NULL. So I guess this is a bug,
but not the bug I'm looking for...
(Note: I know this is an oldish checkout, so maybe someone else has
already found and fixed this)
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