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My First Linux Kernel Patch !!!


patch "staging: rtl8821ae: Fixed the size of array to macro as discussed by" added to staging tree
gregkh@linuxfoundation.org <gregkh@linuxfoundation.org>Fri, Feb 7, 2014 at 9:15 AM
To: surendra.tux@gmail.com, gregkh@linuxfoundation.org, torvalds@linux-foundation.org

This is a note to let you know that I've just added the patch titled

    staging: rtl8821ae: Fixed the size of array to macro as discussed by

to my staging git tree which can be found at
    git://git.kernel.org/pub/scm/linux/kernel/git/gregkh/staging.git
in the staging-linus branch.

The patch will show up in the next release of the linux-next tree
(usually sometime within the next 24 hours during the week.)

The patch will hopefully also be merged in Linus's tree for the
next -rc kernel release.

If you have any questions about this process, please let me know.


From fdf2f40c6cb9649e3990bc11fe0b5c155adf555a Mon Sep 17 00:00:00 2001
From: Surendra Patil <surendra.tux@gmail.com>
Date: Mon, 3 Feb 2014 21:53:53 -0800
Subject: staging: rtl8821ae: Fixed the size of array to macro as discussed by
 Linus
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit

Linus Torvalds writes:

It causes an interesting warning for me:

drivers/staging/rtl8821ae/rtl8821ae/dm.c: In function
‘rtl8821ae_dm_clear_txpower_tracking_state’:
drivers/staging/rtl8821ae/rtl8821ae/dm.c:487:31: warning: iteration 2u
invokes undefined behavior [-Waggressive-loop-optimizations]
   rtldm->bb_swing_idx_ofdm[p] = rtldm->default_ofdm_index;
                               ^
drivers/staging/rtl8821ae/rtl8821ae/dm.c:485:2: note: containing loop
  for (p = RF90_PATH_A; p < MAX_RF_PATH; ++p) {
  ^

and gcc is entirely correct: that loop iterates from 0 to 3, and does this:

                rtldm->bb_swing_idx_ofdm[p] = rtldm->default_ofdm_index;

but the bb_swing_idx_ofdm[] array only has two members. So the last
two iterations will overwrite bb_swing_idx_ofdm_current and the first
entry in bb_swing_idx_ofdm_base[].

Now, the bug does seem to be benign: bb_swing_idx_ofdm_current isn't
actually ever *used* as far as I can tell, and the first entry of
bb_swing_idx_ofdm_base[] will have been written with that same
"rtldm->default_ofdm_index" value.

But gcc is absolutely correct, and that driver needs fixing.

I've pulled it and will let it be because it doesn't seem to be an
issue in practice, but please fix it. The obvious fix would seem to
change the size of "2" to be "MAX_RF_PATH", but I'll abstain from
doing those kinds of changes in the merge when it doesn't seem to
affect the build or functionality).

Reported-By: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Surendra Patil <surendra.tux@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
 drivers/staging/rtl8821ae/wifi.h | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/staging/rtl8821ae/wifi.h b/drivers/staging/rtl8821ae/wifi.h
index cfe88a1efd55..76bef93ad70a 100644
--- a/drivers/staging/rtl8821ae/wifi.h
+++ b/drivers/staging/rtl8821ae/wifi.h
@@ -1414,7 +1414,7 @@ struct rtl_dm {


        /*88e tx power tracking*/
-       u8 bb_swing_idx_ofdm[2];
+       u8 bb_swing_idx_ofdm[MAX_RF_PATH];
        u8 bb_swing_idx_ofdm_current;
        u8 bb_swing_idx_ofdm_base[MAX_RF_PATH];
        bool bb_swing_flag_Ofdm;
--
1.8.5.1.163.gd7aced9





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