Modify trapframe decoding to properly analyze trapframe.
Provide method for fixup_pc. It happens, that in some kernel
functions, the GDB stack frame decoder cannot determine both
func name and frame size. This is because these functions
either contain invalid instruction, or their format does
not match standard schema. Detect that scenarios and move
PC accordingly to jump into known function schema, which
GDB is able to parse.
Obtained from: Semihalf
Sponsored by: Juniper Networks
Reviewed by: kib, zbb
Differential Revision: https://reviews.freebsd.org/D5976
- Add a kvaddr_type to represent kernel virtual addresses instead of
unsigned long.
- Add a struct kvm_nlist which is a stripped down version of struct nlist
that uses kvaddr_t for n_value.
- Add a kvm_native() routine that returns true if an open kvm descriptor
is for a native kernel and memory image.
- Add a kvm_open2() function similar to kvm_openfiles(). It drops the
unused 'swapfile' argument and adds a new function pointer argument for
a symbol resolving function. Native kernels still use _fdnlist() from
libc to resolve symbols if a resolver function is not supplied, but cross
kernels require a resolver.
- Add a kvm_nlist2() function similar to kvm_nlist() except that it uses
struct kvm_nlist instead of struct nlist.
- Add a kvm_read2() function similar to kvm_read() except that it uses
kvaddr_t instead of unsigned long for the kernel virtual address.
- Add a new kvm_arch switch of routines needed by a vmcore backend.
Each backend is responsible for implementing kvm_read2() for a given
vmcore format.
- Use libelf to read headers from ELF kernels and cores (except for
powerpc cores).
- Add internal helper routines for the common page offset hash table used
by the minidump backends.
- Port all of the existing kvm backends to implement a kvm_arch switch and
to be cross-friendly by using private constants instead of ones that
vary by platform (e.g. PAGE_SIZE). Static assertions are present when
a given backend is compiled natively to ensure the private constants
match the real ones.
- Enable all of the existing vmcore backends on all platforms. This means
that libkvm on any platform should be able to perform KVA translation
and read data from a vmcore of any platform.
Tested on: amd64, i386, sparc64 (marius)
Differential Revision: https://reviews.freebsd.org/D3341
* document the kgdb -b flag
* better verify what's valid with -b
* add more comprehensive command line help
PR: kern/175743
Submitted by: Christoph Mallon <christoph.mallon@gmx.de>
This allows a remote session to be specified with '-r' as well as a
non-default baudrate setting using '-b'.
TODO: add to the kgdb manpage.
MFC after: 2 weeks
so that kgdb can be used more like a normal gdb:
- Load the kernel via the standard 'exec' target and allow it to be changed
via the 'file' command.
- Instead of explicitly loading the kernel file as the mail symbol file
during startup, just pass it to gdb_main() as the executable file.
- Change the kld support (via shared libraries) to cache the address of
the linker_files and linker_kernel_file variables in addition to the
offsets of various members in 'struct linker_file'.
- When a new symbol file is loaded, recompute the addresses and offsets
used by the kld support code.
- When a new symbol file is loaded, recalculate the ofs_fix variable to
account for the different ways a trapframe can be passed to trap
frame handlers in i386. This is done by adding a MD
kgdb_trgt_new_objfile() hook that is empty on all but i386.
- Don't use the directory name of the kernel specified on the command
line to find kernel modules in the kld support code. Instead,
extract the filename of the current executable via exec_bfd. Now
the 'kernel' variable is private to main.c again.
- Make the 'add-kld' command explicitly fail if no executable is loaded.
- Make the support for vmcores a real core-dump target that opens the
kernel and vmcore on open and closes the kvm connection when closed, etc.
- The 'core' command can now be used to select a vmcore to use, either
a crash dump file or /dev/mem for live debugging.
- The 'detach' command can be used to detach from a vmcore w/o attaching
to a new one.
- kgdb no longer explicitly opens a core dump during startup and no longer
has to use an atexit() hook to close the kvm connection on shutdown.
- Symbols for kld's are automatically loaded anytime a core is opened.
Also, the unread portion of dmesg is dumped just as it was done on kgdb
startup previously.
- Don't require either a remote target or core dump if a kernel is specified.
You can now just run 'kgdb kernel' similar to running gdb on an executable
and later connect to a remote target or core dump.
- Use a more relaxed way to verify remote targets specified via -r.
Instead of explicitly allowing a few non-file target specifications,
just assume that if stat() on the arg and on "/dev/" + arg both fail
that is some non-file target and pass it to gdb.
- Don't use a custom interpreter. The existing kgdb_init() hook and the
target_new_objfile() hook give us sufficient hooks during startup to
setup kgdb-specific behavior now.
- Always add the 'proc', 'tid', and 'add-kld' commands on startup and not
just if we have a core dump. Currently the 'proc' and 'tid' commands do
not work for remote targets (I will fix at least 'tid' in the next round
of changes though). However, the 'add-kld' command works fine for
loading symbols for a kernel module on a remote target.
- Always setup the 'kld' shared library target operations instead of just
if we have a core dump. Although symbols for kernel modules are not
automatically loaded when connecting to a remote target, you can do
'info sharedlibrary' after connecting to the remote target and kgdb will
find all the modules. You can then use the 'sharedlibrary' command to
load symbols from the module files.
- Change kthr_init() to free the existing list of kthr objects before
generating a new one. This allows it to be invoked multiple times
w/o leaking memory.
MFC after: 1 week
evaluate_expression() so that any errors are caught and cause the function
to return to 0. Otherwise the errors posted an exception (via longjmp())
that aborted the current operation. This fixes the kld handling for
older kernels (6.x and 7.x) that don't have the full pathname stored in
the kernel linker.
MFC after: 3 days
and build a section table from the kernel file so that 'info files' output
for kgdb now matches the usage of gdb on a regular file with the exception
that we don't list sections for memory in the crash dump.
crash dumps with kernel modules. The command is basically a wrapper
around add-symbol-file except that it uses the kernel linker data
structures and the ELF section headers of the kld to calculate the
section addresses add-symbol-file needs.
The 'kld' parameter may either be an absolute path or a relative path.
kgdb looks for the kld in several locations checking for variants with
".symbols" or ".debug" suffixes in each location. The first location it
tries is just opening the specified path (this handles absolute paths and
looks for the kld relative to the current directory otherwise). Next
it tries to find the module in the same directory of the kernel image
being used. If that fails it extracts the kern.module_path from the
kernel being debugged and looks in each of those paths.
The upshot is that for the common cases of debugging /boot/kernel/kernel
where the module is in either /boot/kernel or /boot/modules one can merely
do 'add-kld foo.ko'.
MFC after: 1 week
mode. This allows one to use kgdb on /dev/mem and be able to patch memory
on a live system. This is identical to what -wcore used to do in previous
gdb versions for FreeBSD.
Requested by: wpaul
list of frame sniffers so that trapframes can be detected. The kluge
is needed because this version of gdb only supports appending a
sniffer to the list of sniffers and the moment kgdb gets a chance to
add its own frame sniffer, the target's default frame sniffer is
already in the list. Since the default frame sniffer claims any
frame thrown at it, kgdb's frame sniffer never gets to smell (a
process much akin to tasting, but with lesser chance of hurling :-)
This commit adds dummy frame sniffers that never claim a frame and
as such don't fix anything yet. However, we now have frame sniffers
and they are being called, so it's just a matter of adding meat to
the bones and we'll be able to properly unwind across trapframes.
MFC after: 1 week
static.
o Register a function with atexit(3) to close the KVM object if
we have one open.
o Show the unread portion of the kernel's message buffer before
presenting the prompt. It's bound to provide some useful info.
o Don't call kgdb_target() twice. It results in having all threads
listed twice.
MFC after: 1 week
in future calls, so we can't free it here. The right place to free the
buffer would be to be after kvm_close(), but we don't do that yet. A
static buffer would work too.
Reviewed by: marcel (who has other plans for this anyway)
Approved by: re
it to recognise what ABI to use on amd64 (and possibly others) platform.
Display PID and process name as a part of the 'info threads' output, TIDs
alone are too confusing. Introduce new commmands 'tid <tid>' and 'proc <pid>'
to accompany gdb's default 'thread <thread num>' to make the task of switching
between different contexts easier.
Document all options and general usage.
Implement the -a option to bump the annotation_level. This improves
the Emacs gud behaviour. You can now supply the following function
(defun gud-gdb-massage-args (file args) (cons "-a" args))
(e.g. by evaluating it from the *scratch* buffer) and get the normal
jump to the source window when browsing the stack.
We should probably eventually supply our own kgdb submode to gud.el.
make sure it is a device. GDB special cases these prefixes and treats
:#### as a tcp port on localhost and executes what ever follows '|'.
This allows kgdb to debug via dconschat.
Discussed with: marcel
with the currently running kernel image. Otherwise, one of -c, -n or
-r is expected for working on a particular core file (-c), working
on a saved dump (-n) or working remotely (-r). When working on a
saved dump, a kernel may be omitted.
For a remote debugging session (-r), kgdb(1) will use the specified
device.
is basicly a shell on top of libgdb that knows about kernel threads,
kernel modules and kvm(3). As the word "beginnings" implies, not
all of the features have been implemented yet. The tool is useful
and I'd like feedback on the taken route.
The simplest way to debug a kernel core file is:
kgdb -n 0
This opens /var/crash/vmcore.0 with the corresponding kernel in
the object directory (kernel.debug is used if it exists).
Typical things that need to be added are:
o Auto loading of kernel modules,
o Handling of trapframes so that backtraces can be taken across
them,
o Some fancy commands to extract useful information out of a core
file,
o Various (probably many) other things.
