linux-kernel - Re: [GIT PULL] Staging wireless driver for 3.14-rc1

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Date:	Sat, 1 Feb 2014 10:43:11 -0800
From:	Linus Torvalds <torvalds@...ux-foundation.org>
To:	Greg KH <gregkh@...uxfoundation.org>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Linux Driver Project <devel@...uxdriverproject.org>
Subject: Re: [GIT PULL] Staging wireless driver for 3.14-rc1

On Fri, Jan 31, 2014 at 6:32 AM, Greg KH <gregkh@...uxfoundation.org> wrote:
>
> Here's a single staging driver for a wireless chipset that has shown up
> in the SteamBox hardware.  It is merged separately from the "main"
> staging pull request to sync up with the wireless api changes that came
> in from the networking tree.

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).

               Linus
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