linux-kernel - [PATCH v2] kdb: Avoid array subscript warnings on non-SMP builds

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Date:   Mon, 21 Oct 2019 11:10:56 +0100
From:   Daniel Thompson <daniel.thompson@...aro.org>
To:     Douglas Anderson <dianders@...omium.org>,
        Jason Wessel <jason.wessel@...driver.com>
Cc:     Daniel Thompson <daniel.thompson@...aro.org>,
        kgdb-bugreport@...ts.sourceforge.net, linux-kernel@...r.kernel.org,
        patches@...aro.org, kbuild test robot <lkp@...el.com>
Subject: [PATCH v2] 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.

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)

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>
---

Notes:
    Changes in v2:
    
     - Moved the IS_ENABLED(CONFIG_SMP) test to the first (slightly easier
       to read the code, improves code generation a little)
     - Sent out as a proper patch e-mail ;-)

 kernel/debug/debug_core.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/kernel/debug/debug_core.c b/kernel/debug/debug_core.c
index 70e86b4b4932..2b7c9b67931d 100644
--- a/kernel/debug/debug_core.c
+++ b/kernel/debug/debug_core.c
@@ -444,7 +444,7 @@ int dbg_remove_all_break(void)
 #ifdef CONFIG_KGDB_KDB
 void kdb_dump_stack_on_cpu(int cpu)
 {
-	if (cpu == raw_smp_processor_id()) {
+	if (cpu == raw_smp_processor_id() || !IS_ENABLED(CONFIG_SMP)) {
 		dump_stack();
 		return;
 	}
--
2.21.0