linux-kernel - [PATCH] firmware: declare __{start,end}_builtin

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Date:	Sat, 25 Jun 2016 17:04:33 +0200
From:	Vegard Nossum <vegard.nossum@...cle.com>
To:	Ming Lei <ming.lei@...onical.com>
Cc:	linux-kernel@...r.kernel.org
Subject: [PATCH] firmware: declare __{start,end}_builtin_fw as pointers

The test in this loop:

  for (b_fw = __start_builtin_fw; b_fw != __end_builtin_fw; b_fw++) {

was getting completely compiled out by my gcc, 7.0.0 20160520. The result
was that the loop was going beyond the end of the builtin_fw array and
giving me a page fault when trying to dereference b_fw->name inside
strcmp().

I strongly suspect it's because __start_builtin_fw and __end_builtin_fw
are both declared as (separate) arrays, and so gcc conludes that b_fw can
never point to __end_builtin_fw.

By changing these variables from arrays to pointers, gcc can no longer
assume that these are separate arrays.

Cc: stable@...r.kernel.org
Signed-off-by: Vegard Nossum <vegard.nossum@...cle.com>
---
 drivers/base/firmware_class.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/drivers/base/firmware_class.c b/drivers/base/firmware_class.c
index 773fc30..4dddf7f 100644
--- a/drivers/base/firmware_class.c
+++ b/drivers/base/firmware_class.c
@@ -43,8 +43,8 @@ MODULE_LICENSE("GPL");

 #ifdef CONFIG_FW_LOADER

-extern struct builtin_fw __start_builtin_fw[];
-extern struct builtin_fw __end_builtin_fw[];
+extern struct builtin_fw *__start_builtin_fw;
+extern struct builtin_fw *__end_builtin_fw;

 static bool fw_get_builtin_firmware(struct firmware *fw, const char *name)
 {
-- 
1.9.1