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Message-ID: <20170515190235.GA1740@makrotopia.org> Date: Mon, 15 May 2017 21:02:36 +0200 From: Daniel Golle <daniel@...rotopia.org> To: David Miller <davem@...emloft.net> Cc: arnd@...db.de, sgruszka@...hat.com, helmut.schaa@...glemail.com, kvalo@...eaurora.org, dev@...sin.me, johannes.berg@...el.com, pozega.tomislav@...il.com, vasilugin@...dex.ru, roman@...em.lv, linux-wireless@...r.kernel.org, netdev@...r.kernel.org, linux-kernel@...r.kernel.org Subject: Re: [PATCH] rt2x00: improve calling conventions for register accessors On Mon, May 15, 2017 at 10:40:52AM -0400, David Miller wrote: > From: Arnd Bergmann <arnd@...db.de> > Date: Mon, 15 May 2017 16:36:45 +0200 > > > On Mon, May 15, 2017 at 4:28 PM, Stanislaw Gruszka <sgruszka@...hat.com> wrote: > >> On Mon, May 15, 2017 at 03:46:55PM +0200, Arnd Bergmann wrote: > >>> With CONFIG_KASAN enabled and gcc-7, we get a warning about rather high > >>> stack usage (with a private patch set I have to turn on this warning, > >>> which I intend to get into the next kernel release): > >>> > >>> wireless/ralink/rt2x00/rt2800lib.c: In function 'rt2800_bw_filter_calibration': > >>> wireless/ralink/rt2x00/rt2800lib.c:7990:1: error: the frame size of 2144 bytes is larger than 1536 bytes [-Werror=frame-larger-than=] > >>> > >>> The problem is that KASAN inserts a redzone around each local variable that > >>> gets passed by reference, and the newly added function has a lot of them. > >>> We can easily avoid that here by changing the calling convention to have > >>> the output as the return value of the function. This should also results in > >>> smaller object code, saving around 4KB in .text with KASAN, or 2KB without > >>> KASAN. > >>> > >>> Fixes: 41977e86c984 ("rt2x00: add support for MT7620") > >>> Signed-off-by: Arnd Bergmann <arnd@...db.de> > >>> --- > >>> drivers/net/wireless/ralink/rt2x00/rt2800lib.c | 319 +++++++++++++------------ > >>> 1 file changed, 164 insertions(+), 155 deletions(-) > >> > >> We have read(, &val) calling convention since forever in rt2x00 and that > >> was never a problem. I dislike to change that now to make some tools > >> happy, I think problem should be fixed in the tools instead. > > > > How about adding 'depends on !KASAN' in Kconfig instead? > > Please let's not go down that route and make such facilities less > useful due to decreased coverage. Being the one to blame for submitting the patch adding most of the problem's footprint: Arnd's change looks good to me and I believe it should be merged. This is the type of feedback I was hoping for when submitting all the long-forgotten and rotting patches from OpenWrt's mac80211 driver patches! Thanks to Arnd for your efforts! Consider this as Acked-by: Daniel Golle <daniel@...rotopia.org> for Arnd's original patch (and for NOT adding 'depends on !KASAN') Cheers Daniel > > Thanks.
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