Hi Brian,
Brian Xu - Sun Microsystems - Beijing China wrote:
> Hi,
>
> I have a question: how the cmd '::findstack -v' in mdb works?
>
> Likewise in sparc, since at any time only the current register window
> can be accessed, so if we want to backtrace the stack, we can only
> access the fp(i6) and args(i0-i5) of the function's father, and how we
> can access those of the grandfather, great grandfather, etc?
>
>
|SPARC uses register windows for most argument passing. Basically,
if a function executes the "save" instruction at or near the beginning
and the "restore" instruction at the end, there is a save area for registers
on the stack. When a thread switch occurs, or a window spill trap
occurs (a save executed, but no more windows), the register window(s)
that need to be saved are placed in the save area on the stack.
If a function does not use save/restore, arguments are in the output
registers. There are six registers used for argument passing. If a
function takes more than 6 arguments, the additional arguments are placed
in the caller's frame at a fixed location from the top.
The following shows an example. Note that for 64-bit SPARC, the
stack pointer (%sp) and the frame pointer (%fp) are adjusted by 0x7ff
(the ABI-Bias). The bias is there for two reasons. First, it allows
trap handling code to quickly determine if it needs to save 32-bit
or 64-bit values (with the bias, 64-bit stack pointer is always an odd
number (lowest bit set)). Second, it allows more space to be
accessed using "immediate" addressing (for example, "ld [%fp+offset], %l0").
"offset" is an immediate value and is a signed, 13-bit value. By using the
abi-bias, the range of stack addresses that can be accessed with immediate
addressing is increased. Let me know if you want more information on this.
# *mdb -k*
*::threadlist* *-v* /<-- stack backtrace for all kernel threads/
/< output truncated >/
============== thread_id 30000aa5500
0x30000b2ced9:
process args /usr/sbin/inetd -s /<-- inetd /
0x30000aa5610: lwp procp wchan
30000b4dba0 30000b2ca48 300007fe87a
0x30000aa5538:
pc sp
cv_wait_sig_swap+0x184 2a1003650a1 <-- stack pointer is odd
(i.e., has ABI-bias)//
cv_waituntil_sig+0x14(300007fe87a, 300007fe840, 0, 0, 3b, 20)
poll+0x424(ffbff5f8, 30000998d08, 3000004ec48, ffffffffffffffff, 0, 188)
syscall_trap32+0xa8(ffbff5f8, 31, ffffffffffffffff, 0, 1c, 40)
/< output truncated >/
*2a1003650a1$c* /<-- 2a1003650a1 is sp of inetd/
cv_waituntil_sig+0x14(300007fe87a, 300007fe840, 0, 0, 3b, 20)
poll+0x424(ffbff5f8, 30000998d08, 3000004ec48, ffffffffffffffff, 0, 188)
syscall_trap32+0xa8(ffbff5f8, 31, ffffffffffffffff, 0, 1c, 40)
*2a1003650a1$C* /<-- upper-case $C gives frame pointer at each frame/
000002a100365151 cv_waituntil_sig+0x14(300007fe87a, 300007fe840, 0, 0, 3b, 20)
000002a100365211 poll+0x424(ffbff5f8, 30000998d08, 3000004ec48, ffffffffffffffff
, 0, 188)
000002a1003652f1 syscall_trap32+0xa8(ffbff5f8, 31, ffffffffffffffff, 0, 1c, 40)
*30000aa5500::print kthread_t t_pcb* /<-- get the pc and sp from the thread of
inetd/
{
t_pcb.val = [ 0x107bd1c, 0x2a1003650a1 ]
}
*107bd1c/ai* /<-- same pc as threadlist shows/
cv_wait_sig_swap+0x184:
cv_wait_sig_swap+0x184: call -0x3aeb4
|
The following shows the register save areas for each stack frame for
|inetd|.
|
*2a1003650a1+7ff,10/K* /<-- must add V9 bias, display 16 64-bit hex values/
0x2a1003658a0: 30000b4dba0 30000b2ca48 0 300007fe87a
/<-- %l0-%l3/
938 0 30000aa5500 fffd
/<-- %l4-%l7/
0 300007fe840 20 3000004edce
/<-- %i0-%i3/
2a100365a00 0 2a100365151 107c14c
/<-- %i4-%i7/
*107c14c/ai* /<-- %i7 is saved program counter/
cv_waituntil_sig+0x14:
cv_waituntil_sig+0x14: call -0x5b4
*2a100365151+7ff,10/K* /<-- %i6 is saved frame pointer, use to get previous
frame/
0x2a100365950: 0 3000004ec48 3b 0
30000c05798 30 300007fe840 30000bbb600
300007fe87a 300007fe840 0 0
3b 20 2a100365211 10bb378
*10bb378/ai* /<-- and repeat.../
poll+0x424:
poll+0x424: call -0x3f240
*2a100365211+7ff,10/K*
0x2a100365a10: 30000998d48 300007fe840 0 31
30000998d58 0 0 0
ffbff5f8 30000998d08 3000004ec48
ffffffffffffffff 0 188
2a1003652f1 10343fc
*10343fc/ai* /<-- and again.../
syscall_trap32+0xa8:
syscall_trap32+0xa8: jmpl %g3, %o7
*2a1003652f1+7ff,10/K*
0x2a100365af0: 1007254 2a100365ba0 30000b4dba0 1034354
1448000 0 30000aa5500 2a100365ba0
ffbff5f8 31 ffffffffffffffff
0 1c 40 ffbff598
ff14d474
*ff14d474/ai* /<-- and again, but here kernel is returning to user address/
0xff14d474:
mdb: failed to read instruction at ff14d474: no mapping for address
0xff14d474:
In the above output, each frame's window save area is displayed.
Hope this helps. For 32-bit programs, the technique is the same, only you don't
add 7ff, since the ABI-bias is not used.
Basically, ::findstack does the same walk that I am doing by hand in
the above output.
max
|
> Thanks,
> Brian
>
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>
>
