linux-kernel - Re: [danielt-linux:kgdb/for-next 4/4] kernel/debug/debug_core.c:452:17: warning: array subscript is outside array bounds

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Date:   Mon, 14 Oct 2019 17:28:47 +0100
From:   Daniel Thompson <daniel.thompson@...aro.org>
To:     Douglas Anderson <dianders@...omium.org>
Cc:     Jason Wessel <jason.wessel@...driver.com>,
        kgdb-bugreport@...ts.sourceforge.net, linux-kernel@...r.kernel.org
Subject: Re: [danielt-linux:kgdb/for-next 4/4]
 kernel/debug/debug_core.c:452:17: warning: array subscript is outside array
 bounds

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@...el.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@...aro.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@...el.com>
Fixes: 2277b492582d ("kdb: Fix stack crawling on 'running' CPUs that aren't the master")
Signed-off-by: Daniel Thompson <daniel.thompson@...aro.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