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Message-Id: <20170515.104052.1376354562934671974.davem@davemloft.net> Date: Mon, 15 May 2017 10:40:52 -0400 (EDT) From: David Miller <davem@...emloft.net> To: arnd@...db.de Cc: sgruszka@...hat.com, helmut.schaa@...glemail.com, kvalo@...eaurora.org, daniel@...rotopia.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 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. Thanks.
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