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Add a description of how to use a firewire connection to debug a

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remote system without stopping it.
This commit is contained in:
Greg Lehey 2003-12-31 01:25:07 +00:00
parent 783a364bf8
commit 279b7e129f
1 changed files with 48 additions and 1 deletions
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49
share/man/man4/gdb.4
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@ -239,7 +239,7 @@ Finally, establish connection:
.Bd -literal -offset 5m
# \f(CBgdb kernel.debug\fP
GNU gdb 5.2.1 (FreeBSD)
\&\fI(politcal statements omitted)\fP\/
\&\fI(political statements omitted)\fP\/
Ready to go. Enter 'tr' to connect to the remote target
with /dev/cuaa0, 'tr /dev/cuaa1' to connect to a different port
or 'trf portno' to connect to the remote target with the firewire
@ -277,6 +277,53 @@ Then establish connection with:
.Ed
.Pp
.El
.Ss Non-cooperative debugging a live system with a remote firewire link
In addition to the conventional debugging via firewire described in the previous
section, it is possible to debug a remote system without its cooperation, once
an initial connection has been established.
This corresponds to debugging a local machine using
.Pa /dev/mem .
It can be very useful if a system crashes and the debugger no longer responds.
To use this method, set the
.Nm sysctl
variables
.Va hw.firewire.fwmem.eui64_hi
and
.Va hw.firewire.fwmem.eui64_lo
to the upper and lower halves of the EUI64 ID of the remote system respectively.
From the previous example, the remote machine shows:
.Bd -literal -offset 5m
# \f(CBfwcontrol\fP
2 devices (info_len=2)
node EUI64 status
0 0x000199000003622b 0
1 0x00c04f3226e88061 1
.Ed
.Pp
Enter:
.Bd -literal -offset 5m
# \f(CBsysctl -w hw.firewire.fwmem.eui64_hi=0x00019900\fP
hw.firewire.fwmem.eui64_hi: 0 -> 104704
# \f(CBsysctl -w hw.firewire.fwmem.eui64_lo=0x0003622b\fP
hw.firewire.fwmem.eui64_lo: 0 -> 221739
.Ed
.Pp
Note that the variables must be explicitly stated in hexadecimal.
After this, you can examine the remote machine's state with the following input:
.Bd -literal -offset 5m
# \f(CBgdb -k kernel.debug /dev/fwmem0.0\fP
GNU gdb 5.2.1 (FreeBSD)
\&\fI(messages omitted)\fP\/
Reading symbols from /boot/kernel/dcons.ko...done.
Loaded symbols for /boot/kernel/dcons.ko
Reading symbols from /boot/kernel/dcons_crom.ko...done.
Loaded symbols for /boot/kernel/dcons_crom.ko
#0 sched_switch (td=0xc0922fe0) at /usr/src/sys/kern/sched_4bsd.c:621
0xc21bd378 in ?? ()
.Ed
.Pp
In this case, it's not necessary to load the symbols explicitly.
The remote system continues to run.
.Sh COMMANDS
The user interface to
.Nm