cvs commit: src/gnu/usr.bin/gdb/kgdb kgdb.h kld.c trgt.c

John Baldwin jhb at
Mon Jan 28 15:09:36 PST 2008

On Monday 28 January 2008 04:40:10 pm John Baldwin wrote:
> jhb         2008-01-28 21:40:10 UTC
>   FreeBSD src repository
>   Modified files:
>     gnu/usr.bin/gdb/kgdb kgdb.h kld.c trgt.c 
>   Log:
>   Add support for automatically loading symbols for kld's on startup:
>   - Add a new 'kgdb_auto_load_klds()' routine which is invoked during
>     startup that walks the list of linker files and tries to find a matching
>     kld on disk for each non-kernel kld.  If a kld file is found, then it
>     is added as if the 'add-kld' command is invoked.  One change from
>     'add-kld' is that this method attempts to use the 'pathname' from the
>     linker_file structure first to try to load the file.  If that fails
>     it then looks in the kernel directory followed by the directories in
>     the module path.
>   - Move the kld file suffix handling into a separate routine so that it
>     can be called standalone and to reduce duplicate code in 
>   - Cache the offsets of members of 'struct linker_file' during startup
>     instead of computing them for each 'add-kld'.
>   - Use GDB's target_read_string() instead of direct KVM access.
>   - Add all resident sections from a kld by using bfd_map_over_sections() to
>     build the section list rather than just adding symbols for ".text",
>     ".data", ".bss", and ".rodata".
>   - Change the 'add-kld' command to do a y/n prompt before adding the
>     symbols when run interactively to match 'add-symbol-file'.

Now 'add-kld' can be optional, you can always use it if the automatic magic 
picks a poor foo.ko (e.g. a stripped one w/o symbols).  Example:

> sudo ./kgdb -q -c /usr/crash/vmcore.10 /boot/kernel/kernel
[GDB will not be able to debug user-mode threads: /usr/lib/ 
Undefined symbol "ps_pglobal_lookup"]
Loaded symbols for kld "crash.ko" from "/boot/modules/crash.ko"
#0  doadump () at pcpu.h:195
195     pcpu.h: No such file or directory.
        in pcpu.h
(kgdb) where
#0  doadump () at pcpu.h:195
#1  0xc05d399c in boot (howto=260) at /usr/src/sys/kern/kern_shutdown.c:417
#2  0xc05d3c0a in panic (fmt=Variable "fmt" is not available.
) at /usr/src/sys/kern/kern_shutdown.c:571
#3  0xc08115d9 in dblfault_handler () at /usr/src/sys/i386/i386/trap.c:927
#4  0xc05c6220 in mtx_pool_setup_dynamic ()
#5  0xc065e125 in arc4rand (ptr=0xe61b0168, len=4, reseed=0)
    at /usr/src/sys/libkern/arc4random.c:142
#6  0xc065e171 in arc4random () at /usr/src/sys/libkern/arc4random.c:150
#7  0xc3d43402 in blow_stack () at crash.c:773
#8  0xc3d43410 in blow_stack () at crash.c:764
#9  0xc3d43410 in blow_stack () at crash.c:764

(Note that blow_stack() is in crash.ko and the stack trace worked right away.)

It even works for the live kernel (scary):

> sudo ./kgdb -q /boot/kernel/kernel /dev/mem
[GDB will not be able to debug user-mode threads: /usr/lib/ 
Undefined symbol "ps_pglobal_lookup"]
Loaded symbols for kld "iwi_bss.ko" from "/boot/kernel/iwi_bss.ko"
Loaded symbols for kld "logo_saver.ko" from "/boot/kernel/logo_saver.ko"
#0  sched_switch (td=0xc08fdb90, newtd=Variable "newtd" is not available.
) at /usr/src/sys/kern/sched_ule.c:1905
1905                    cpuid = PCPU_GET(cpuid);

Now just need to axe that '[GDB will not be able blah blah blah]' message.

Note that you can't see which kld's are loaded currently.  At some point I 
will rewrite the kld support to actually hook into GDB's shared library 
support so that 'info sharedlibrary' will work.  I'm slowly learning GDB 
internals, but that bit will probably take a while.

John Baldwin

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