linux-toradex.git/arch/mips/kernel/kgdb.c, branch v4.19

MIPS: KGDB: Use kernel context for sleeping threads

2017-04-12T20:29:22+00:00

KGDB is a kernel debug stub and it can't be used to debug userland as it
can only safely access kernel memory.

On MIPS however KGDB has always got the register state of sleeping
processes from the userland register context at the beginning of the
kernel stack. This is meaningless for kernel threads (which never enter
userland), and for user threads it prevents the user seeing what it is
doing while in the kernel:

(gdb) info threads
  Id   Target Id         Frame
  ...
  3    Thread 2 (kthreadd) 0x0000000000000000 in ?? ()
  2    Thread 1 (init)   0x000000007705c4b4 in ?? ()
  1    Thread -2 (shadowCPU0) 0xffffffff8012524c in arch_kgdb_breakpoint () at arch/mips/kernel/kgdb.c:201

Get the register state instead from the (partial) kernel register
context stored in the task's thread_struct for resume() to restore. All
threads now correctly appear to be in context_switch():

(gdb) info threads
  Id   Target Id         Frame
  ...
  3    Thread 2 (kthreadd) context_switch (rq=, cookie=..., next=, prev=0x0) at kernel/sched/core.c:2903
  2    Thread 1 (init)   context_switch (rq=, cookie=..., next=, prev=0x0) at kernel/sched/core.c:2903
  1    Thread -2 (shadowCPU0) 0xffffffff8012524c in arch_kgdb_breakpoint () at arch/mips/kernel/kgdb.c:201

Call clobbered registers which aren't saved and exception registers
(BadVAddr & Cause) which can't be easily determined without stack
unwinding are reported as 0. The PC is taken from the return address,
such that the state presented matches that found immediately after
returning from resume().

Fixes: 8854700115ec ("[MIPS] kgdb: add arch support for the kernel's kgdb core")
Signed-off-by: James Hogan 
Cc: Jason Wessel 
Cc: linux-mips@linux-mips.org
Cc: stable@vger.kernel.org
Patchwork: https://patchwork.linux-mips.org/patch/15829/
Signed-off-by: Ralf Baechle

Replace with globally

2016-12-24T19:46:01+00:00

This was entirely automated, using the script by Al:

  PATT='^[[:blank:]]*#[[:blank:]]*include[[:blank:]]*'
  sed -i -e "s!$PATT!#include !" \
        $(git grep -l "$PATT"|grep -v ^include/linux/uaccess.h)

to do the replacement at the end of the merge window.

Requested-by: Al Viro 
Signed-off-by: Linus Torvalds

MIPS: Get rid of 'kgdb_early_setup' cruft.

2015-06-21T19:54:10+00:00

Commit 854700115ecf ([MIPS] kgdb: add arch support for the kernel's kgdb core)
added the 'kgdb_early_setup' flag to avoid  calling trap_init() and init_IRQ()
the second time, however the code that called these functions earlier,  from
kgdb_arch_init(), had been already removed by that  time,  so the flag never
served any useful purpose. Remove the related code along with ugly #ifdef'ery
at last.

[ralf@linux-mips.org: Folded in Guenter Roeck's fix.]

Signed-off-by: Sergei Shtylyov 
Patchwork: https://patchwork.linux-mips.org/patch/10501/
Signed-off-by: Guenter Roeck 
Patchwork: https://patchwork.linux-mips.org/patch/10533/
Signed-off-by: Ralf Baechle

MIPS: kernel: {ftrace,kgdb}: Set correct address limit for cache flushes

2014-03-26T22:09:18+00:00

When flushing the icache, make sure the address limit is correct
so the appropriate 'cache' instruction will be used. This has no
impact on cores operating in non-eva mode. However, when EVA is
enabled, we ensure that 'cache' will be used instead of 'cachee'.

Signed-off-by: Leonid Yegoshin 
Signed-off-by: Markos Chandras

MIPS: Whitespace cleanup.

2013-02-01T09:00:22+00:00

Having received another series of whitespace patches I decided to do this
once and for all rather than dealing with this kind of patches trickling
in forever.

Signed-off-by: Ralf Baechle

mips,kgdb: fix recursive page fault with CONFIG_KPROBES

2012-10-12T11:37:34+00:00

This fault was detected using the kgdb test suite on boot and it
crashes recursively due to the fact that CONFIG_KPROBES on mips adds
an extra die notifier in the page fault handler.  The crash signature
looks like this:

kgdbts:RUN bad memory access test
KGDB: re-enter exception: ALL breakpoints killed
Call Trace:
[<807b7548>] dump_stack+0x20/0x54
[<807b7548>] dump_stack+0x20/0x54

The fix for now is to have kgdb return immediately if the fault type
is DIE_PAGE_FAULT and allow the kprobe code to decide what is supposed
to happen.

Cc: Masami Hiramatsu 
Cc: David S. Miller 
Cc: 
Signed-off-by: Jason Wessel

MIPS: Fix a typo.

2010-10-04T17:33:54+00:00

"Userpace" -> "Userspace"

Signed-off-by: Andrea Gelmini 
Cc: Andrea Gelmini 
Cc: Jason Wessel 
Cc: Martin Hicks 
Cc: linux-mips@linux-mips.org
Patchwork: https://patchwork.linux-mips.org/patch/1536/
Signed-off-by: Ralf Baechle

kgdb,mips: remove unused kgdb_cpu_doing_single_step operations

2010-08-05T14:22:25+00:00

The mips kgdb specific code does not support software or HW single
stepping so it should not implement

Signed-off-by: Jason Wessel 
Signed-off-by: Dongdong Deng 
Acked-by: Ralf Baechle 
CC: linux-mips@linux-mips.org

kgdb,mips: Individual register get/set for mips

2010-08-05T14:22:21+00:00

Implement the ability to individually get and set registers for kdb
and kgdb for mips.

Signed-off-by: Jason Wessel 
Acked-by: Ralf Baechle 
CC: linux-mips@linux-mips.org

mips,kgdb: kdb low level trap catch and stack trace

2010-05-21T02:04:26+00:00

The only way the debugger can handle a trap in inside rcu_lock,
notify_die, or atomic_notifier_call_chain without a recursive fault is
to have a low level "first opportunity handler" do_trap_or_bp() handler.

Generally this will be something the vast majority of folks will not
need, but for those who need it, it is added as a kernel .config
option called KGDB_LOW_LEVEL_TRAP.

Also added was a die notification for oops such that kdb can catch an
oops for analysis.

There appeared to be no obvious way to pass the struct pt_regs from
the original exception back to the stack back tracer, so a special
case was added to show_stack() for when kdb is active because you
generally desire to generally look at the back trace of the original
exception.

Signed-off-by: Jason Wessel 
Acked-by: Ralf Baechle