I recently tried using KDB on a 3.0.1 kernel, on an x86 target, using
a fairly-close-to-default kernel configuration.
I found that I could not set a breakpoint.
It sets inside KDB, but then fails to apply the breakpoint when
resuming to user space:
--------------------------------
/proc # echo g >sysrq-trigger
[2689816.806249] SysRq : DEBUG
Entering kdb (current=0xc7661d40, pid 511) on processor 0 due to Keyboard Entry
[0]kdb> bp sys_sync
Instruction(i) BP #0 at 0xc111ce70 (sys_sync)
is enabled addr at 00000000c111ce70, hardtype=0 installed=0
[0]kdb> g
_kdb_bp_install: failed to set breakpoint at 0xc111ce70
/proc # sync
/proc #
--------------------------------
I discovered that this was due to the text segment being marked
read-only, by mark_rodata_ro() in arch/x86/mm/init_32.c
This is controlled by CONFIG_DEBUG_RODATA. With CONFIG_DEBUG_RODATA=y,
I get the following message on startup:
Write protecting the kernel read-only data: 6245
Also, breakpoints don't work.
Turning this off solves the problem, but seems counter-intuitive.
CONFIG_DEBUG_RODATA depends on CONFIG_DEBUG_KERNEL.
Should I:
1) turn off CONFIG_DEBUG_RODATA automatically when CONFIG_KGDB_KDB is set?
or
2) make CONFIG_DEBUG_RODATA depend on !KGDB_KDB?
or
3) something else more subtle?
Thanks,
-- Tim
=============================
Tim Bird
Architecture Group Chair, CE Workgroup of the Linux Foundation
Senior Staff Engineer, Sony Network Entertainment
=============================
------------------------------------------------------------------------------
All the data continuously generated in your IT infrastructure contains a
definitive record of customers, application performance, security
threats, fraudulent activity and more. Splunk takes this data and makes
sense of it. Business sense. IT sense. Common sense.
http://p.sf.net/sfu/splunk-d2dcopy1
_______________________________________________
Kgdb-bugreport mailing list
[email protected]
https://lists.sourceforge.net/lists/listinfo/kgdb-bugreport
