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.TH BT 1 "15 March 1999"
.SH NAME
bt \- Stack Traceback command
.SH SYNOPSIS
bt [ <stack-frame-address> ]
.LP
btp <pid>
.SH DESCRIPTION
The
.B bt
command is used to print a stack traceback. It uses the
current registers (see \fBrd\fP command) to determine
the starting context and attempts to provide a complete
stack traceback for the active thread. If \fIstack-frame-address\fP
is supplied, it is assumed to point to the start of a valid
stack frame and the stack will be traced back from that
point (e.g. on i386 architecture, \fIstack-frame-address\fP
should be the stack address of a saved \fB%eip\fP value from a \fBcall\fP
instruction).
.P
A kernel configuration option \fBCONFIG_KDB_FRAMEPTR\fP should
be enabled so that the compiler will utilize the frame pointer
register properly to maintain a stack which can be correctly
analyzed.
.P
The \fBbt\fP command will attempt to analyze the stack without
frame pointers if the \fBCONFIG_KDB_FRAMEPTR\fP option is not
enabled, but the analysis is difficult and may not produce
accurate nor complete results.
.P
The \fBbtp\fP command will analyze the stack for the given
process identification (see the \fBps\fP command).
.SH LIMITATIONS
If the kernel is compiled without frame pointers, stack tracebacks
may be incomplete. The \fBmds %esp\fP command may be useful in
attemping to determine the actual stack traceback manually.
.P
The \fBbt\fP command may print more arguments for a function
than that function accepts; this happens when the C compiler
doesn't immediately pop the arguments off the stack upon return
from a called function. When this is this case, these extra
stack words will be considered additional arguments by the \fBbt\fP
command.
.SH ENVIRONMENT
The \fBBTARGS\fP environment variable governs the maximum number
of arguments that are printed for any single function.
.SH SMP CONSIDERATIONS
None.
.SH EXAMPLES
.nf
.na
.ft CW
[root@host /root]# cat /proc/partitions
Entering kdb on processor 0 due to Debug Exception @ 0xc01845e3
Read/Write breakpoint #1 at 0xc024ddf4
kdb> bt
EBP Caller Function(args)
0xc74f5f44 0xc0146166 get_partition_list(0xc74d8000)
0xc74f5f8c 0xc01463f3 get_root_array(0xc74d8000, 0x13, 0xc74f5f88, 0xf3, 0xc00)
0xc74f5fbc 0xc0126138 array_read(0xc76cd80, 0x804aef8, 0xc00, 0xc76cdf94)
0xbffffcd4 0xc0108b30 sys_read(0x3, 0x804aef8, 0x1000, 0x1000, 0x804aef8)
kdb> bp
Instruction Breakpoint #0 at 0xc0111ab8 (schedule) in dr0 is disabled on cpu 0
Data Access Breakpoint #1 at 0xc024ddf4 (gendisk_head) in dr1 is enabled on cpu 0
for 4 bytes
kdb> go
[root@host /root]#
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