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* [danielt-linux:kgdb/for-next 4/4] kernel/debug/debug_core.c:452:17: warning: array subscript is outside array bounds
@ 2019-10-10 16:41 kbuild test robot
  2019-10-14 16:28 ` Daniel Thompson
  0 siblings, 1 reply; 3+ messages in thread
From: kbuild test robot @ 2019-10-10 16:41 UTC (permalink / raw)
  To: kbuild-all

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tree:   https://git.kernel.org/pub/scm/linux/kernel/git/danielt/linux.git kgdb/for-next
head:   2277b492582d5525244519f60da6f9daea5ef41a
commit: 2277b492582d5525244519f60da6f9daea5ef41a [4/4] kdb: Fix stack crawling on 'running' CPUs that aren't the master
config: sh-allyesconfig (attached as .config)
compiler: sh4-linux-gcc (GCC) 7.4.0
reproduce:
        wget https://raw.githubusercontent.com/intel/lkp-tests/master/sbin/make.cross -O ~/bin/make.cross
        chmod +x ~/bin/make.cross
        git checkout 2277b492582d5525244519f60da6f9daea5ef41a
        # save the attached .config to linux build tree
        GCC_VERSION=7.4.0 make.cross ARCH=sh 

If you fix the issue, kindly add following tag
Reported-by: kbuild test robot <lkp@intel.com>

Note: it may well be a FALSE warning. FWIW you are at least aware of it now.

All warnings (new ones prefixed by >>):

   kernel/debug/debug_core.c: In function 'kdb_dump_stack_on_cpu':
>> kernel/debug/debug_core.c:452:17: warning: array subscript is outside array bounds [-Warray-bounds]
     if (!(kgdb_info[cpu].exception_state & DCPU_IS_SLAVE)) {
           ~~~~~~~~~^~~~~
   kernel/debug/debug_core.c:469:33: warning: array subscript is outside array bounds [-Warray-bounds]
     kgdb_info[cpu].exception_state |= DCPU_WANT_BT;
   kernel/debug/debug_core.c:470:18: warning: array subscript is outside array bounds [-Warray-bounds]
     while (kgdb_info[cpu].exception_state & DCPU_WANT_BT)
            ~~~~~~~~~^~~~~

vim +452 kernel/debug/debug_core.c

   443	
   444	#ifdef CONFIG_KGDB_KDB
   445	void kdb_dump_stack_on_cpu(int cpu)
   446	{
   447		if (cpu == raw_smp_processor_id()) {
   448			dump_stack();
   449			return;
   450		}
   451	
 > 452		if (!(kgdb_info[cpu].exception_state & DCPU_IS_SLAVE)) {
   453			kdb_printf("ERROR: Task on cpu %d didn't stop in the debugger\n",
   454				   cpu);
   455			return;
   456		}
   457	
   458		/*
   459		 * In general, architectures don't support dumping the stack of a
   460		 * "running" process that's not the current one.  From the point of
   461		 * view of the Linux, kernel processes that are looping in the kgdb
   462		 * slave loop are still "running".  There's also no API (that actually
   463		 * works across all architectures) that can do a stack crawl based
   464		 * on registers passed as a parameter.
   465		 *
   466		 * Solve this conundrum by asking slave CPUs to do the backtrace
   467		 * themselves.
   468		 */
   469		kgdb_info[cpu].exception_state |= DCPU_WANT_BT;
   470		while (kgdb_info[cpu].exception_state & DCPU_WANT_BT)
   471			cpu_relax();
   472	}
   473	#endif
   474	

---
0-DAY kernel test infrastructure                Open Source Technology Center
https://lists.01.org/pipermail/kbuild-all                   Intel Corporation

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^ permalink raw reply	[flat|nested] 3+ messages in thread
* Re: [danielt-linux:kgdb/for-next 4/4] kernel/debug/debug_core.c:452:17: warning: array subscript is outside array bounds
  2019-10-10 16:41 [danielt-linux:kgdb/for-next 4/4] kernel/debug/debug_core.c:452:17: warning: array subscript is outside array bounds kbuild test robot
@ 2019-10-14 16:28 ` Daniel Thompson
  2019-10-14 23:51   ` Doug Anderson
  0 siblings, 1 reply; 3+ messages in thread
From: Daniel Thompson @ 2019-10-14 16:28 UTC (permalink / raw)
  To: Douglas Anderson; +Cc: Jason Wessel, kgdb-bugreport, linux-kernel

Hi Doug

On Fri, Oct 11, 2019 at 12:41:31AM +0800, kbuild test robot wrote:
> tree:   https://git.kernel.org/pub/scm/linux/kernel/git/danielt/linux.git kgdb/for-next
> head:   2277b492582d5525244519f60da6f9daea5ef41a
> commit: 2277b492582d5525244519f60da6f9daea5ef41a [4/4] kdb: Fix stack crawling on 'running' CPUs that aren't the master
> config: sh-allyesconfig (attached as .config)
> compiler: sh4-linux-gcc (GCC) 7.4.0
> reproduce:
>         wget https://raw.githubusercontent.com/intel/lkp-tests/master/sbin/make.cross -O ~/bin/make.cross
>         chmod +x ~/bin/make.cross
>         git checkout 2277b492582d5525244519f60da6f9daea5ef41a
>         # save the attached .config to linux build tree
>         GCC_VERSION=7.4.0 make.cross ARCH=sh 
> 
> If you fix the issue, kindly add following tag
> Reported-by: kbuild test robot <lkp@intel.com>
> 
> Note: it may well be a FALSE warning. FWIW you are at least aware of it now.
> 
> All warnings (new ones prefixed by >>):
> 
>    kernel/debug/debug_core.c: In function 'kdb_dump_stack_on_cpu':
> >> kernel/debug/debug_core.c:452:17: warning: array subscript is outside array bounds [-Warray-bounds]
>      if (!(kgdb_info[cpu].exception_state & DCPU_IS_SLAVE)) {
>            ~~~~~~~~~^~~~~
>    kernel/debug/debug_core.c:469:33: warning: array subscript is outside array bounds [-Warray-bounds]
>      kgdb_info[cpu].exception_state |= DCPU_WANT_BT;
>    kernel/debug/debug_core.c:470:18: warning: array subscript is outside array bounds [-Warray-bounds]
>      while (kgdb_info[cpu].exception_state & DCPU_WANT_BT)
>             ~~~~~~~~~^~~~~

Thoughts on the following?

From 9e0114bc9ae504c3a7e837c977d64f84b2010d8e Mon Sep 17 00:00:00 2001
From: Daniel Thompson <daniel.thompson@linaro.org>
Date: Fri, 11 Oct 2019 08:49:29 +0100
Subject: [PATCH] kdb: Avoid array subscript warnings on non-SMP builds

Recent versions of gcc (reported on gcc-7.4) issue array subscript
warnings for builds where SMP is not enabled.

There is no bug here but there is scope to improve the code
generation for non-SMP systems (whilst also silencing the warning).

Reported-by: kbuild test robot <lkp@intel.com>
Fixes: 2277b492582d ("kdb: Fix stack crawling on 'running' CPUs that aren't the master")
Signed-off-by: Daniel Thompson <daniel.thompson@linaro.org>
---
 kernel/debug/debug_core.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/kernel/debug/debug_core.c b/kernel/debug/debug_core.c
index 70e86b4b4932..eccb7298a0b5 100644
--- a/kernel/debug/debug_core.c
+++ b/kernel/debug/debug_core.c
@@ -449,7 +449,8 @@ void kdb_dump_stack_on_cpu(int cpu)
 		return;
 	}
 
-	if (!(kgdb_info[cpu].exception_state & DCPU_IS_SLAVE)) {
+	if (!IS_ENABLED(CONFIG_SMP) ||
+	    !(kgdb_info[cpu].exception_state & DCPU_IS_SLAVE)) {
 		kdb_printf("ERROR: Task on cpu %d didn't stop in the debugger\n",
 			   cpu);
 		return;
-- 
2.21.0


^ permalink raw reply related	[flat|nested] 3+ messages in thread
* Re: [danielt-linux:kgdb/for-next 4/4] kernel/debug/debug_core.c:452:17: warning: array subscript is outside array bounds
  2019-10-14 16:28 ` Daniel Thompson
@ 2019-10-14 23:51   ` Doug Anderson
  0 siblings, 0 replies; 3+ messages in thread
From: Doug Anderson @ 2019-10-14 23:51 UTC (permalink / raw)
  To: Daniel Thompson; +Cc: Jason Wessel, kgdb-bugreport, LKML

Hi,

On Mon, Oct 14, 2019 at 9:28 AM Daniel Thompson
<daniel.thompson@linaro.org> wrote:
>
> Hi Doug
>
> On Fri, Oct 11, 2019 at 12:41:31AM +0800, kbuild test robot wrote:
> > tree:   https://git.kernel.org/pub/scm/linux/kernel/git/danielt/linux.git kgdb/for-next
> > head:   2277b492582d5525244519f60da6f9daea5ef41a
> > commit: 2277b492582d5525244519f60da6f9daea5ef41a [4/4] kdb: Fix stack crawling on 'running' CPUs that aren't the master
> > config: sh-allyesconfig (attached as .config)
> > compiler: sh4-linux-gcc (GCC) 7.4.0
> > reproduce:
> >         wget https://raw.githubusercontent.com/intel/lkp-tests/master/sbin/make.cross -O ~/bin/make.cross
> >         chmod +x ~/bin/make.cross
> >         git checkout 2277b492582d5525244519f60da6f9daea5ef41a
> >         # save the attached .config to linux build tree
> >         GCC_VERSION=7.4.0 make.cross ARCH=sh
> >
> > If you fix the issue, kindly add following tag
> > Reported-by: kbuild test robot <lkp@intel.com>
> >
> > Note: it may well be a FALSE warning. FWIW you are at least aware of it now.
> >
> > All warnings (new ones prefixed by >>):
> >
> >    kernel/debug/debug_core.c: In function 'kdb_dump_stack_on_cpu':
> > >> kernel/debug/debug_core.c:452:17: warning: array subscript is outside array bounds [-Warray-bounds]
> >      if (!(kgdb_info[cpu].exception_state & DCPU_IS_SLAVE)) {
> >            ~~~~~~~~~^~~~~
> >    kernel/debug/debug_core.c:469:33: warning: array subscript is outside array bounds [-Warray-bounds]
> >      kgdb_info[cpu].exception_state |= DCPU_WANT_BT;
> >    kernel/debug/debug_core.c:470:18: warning: array subscript is outside array bounds [-Warray-bounds]
> >      while (kgdb_info[cpu].exception_state & DCPU_WANT_BT)
> >             ~~~~~~~~~^~~~~
>
> Thoughts on the following?
>
> From 9e0114bc9ae504c3a7e837c977d64f84b2010d8e Mon Sep 17 00:00:00 2001
> From: Daniel Thompson <daniel.thompson@linaro.org>
> Date: Fri, 11 Oct 2019 08:49:29 +0100
> Subject: [PATCH] kdb: Avoid array subscript warnings on non-SMP builds
>
> Recent versions of gcc (reported on gcc-7.4) issue array subscript
> warnings for builds where SMP is not enabled.
>
> There is no bug here but there is scope to improve the code
> generation for non-SMP systems (whilst also silencing the warning).
>
> Reported-by: kbuild test robot <lkp@intel.com>
> Fixes: 2277b492582d ("kdb: Fix stack crawling on 'running' CPUs that aren't the master")
> Signed-off-by: Daniel Thompson <daniel.thompson@linaro.org>
> ---
>  kernel/debug/debug_core.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
>
> diff --git a/kernel/debug/debug_core.c b/kernel/debug/debug_core.c
> index 70e86b4b4932..eccb7298a0b5 100644
> --- a/kernel/debug/debug_core.c
> +++ b/kernel/debug/debug_core.c
> @@ -449,7 +449,8 @@ void kdb_dump_stack_on_cpu(int cpu)
>                 return;
>         }
>
> -       if (!(kgdb_info[cpu].exception_state & DCPU_IS_SLAVE)) {
> +       if (!IS_ENABLED(CONFIG_SMP) ||
> +           !(kgdb_info[cpu].exception_state & DCPU_IS_SLAVE)) {

Thanks for sending this!  I saw the alert but I was on vacation last
Friday and today has been a trainwreck.

I guess my first thought is that this fix is slightly confusing to
read.  Reading it makes you think that if we don't have SMP that we'll
print:

  ERROR: Task on cpu %d didn't stop in the debugger

It took me a second to realize that of course this would never print
because if we're ot on SMP then the first "if" test would trip and
we'd return.  Which makes me wonder why we couldn't instead change
that "if" test to:

 if (!IS_ENABLED(CONFIG_SMP) || cpu == raw_smp_processor_id()) {

...and be done with it.

---

As far as the "there is no bug here", I actually wonder.  We are
always called with a cpu that we got from "kdb_process_cpu(p)", right?
 That function sets cpu to 0 if "cpu > num_possible_cpus()".  ...but
shouldn't it be >=?  I guess task_cpu() probably returned something
sane anyway...

I also find it a little odd that kdb_process_cpu() returns a signed
int even though task_cpu() returns an unsigned one, but I guess we
don't need to worry about the case where the number of CPUs can't fit
into a signed int?

---

Hopefully that's all correct.  I'm just about outta time and I wanted
to send something off.  If something looks wrong it probably is...

-Doug

^ permalink raw reply	[flat|nested] 3+ messages in thread
end of thread, other threads:[~2019-10-14 23:51 UTC | newest]

Thread overview: 3+ messages (download: mbox.gz / follow: Atom feed)
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2019-10-10 16:41 [danielt-linux:kgdb/for-next 4/4] kernel/debug/debug_core.c:452:17: warning: array subscript is outside array bounds kbuild test robot
2019-10-14 16:28 ` Daniel Thompson
2019-10-14 23:51   ` Doug Anderson

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