linux-kernel - Re: [PATCH] mtd: lpddr: fix excessive stack usage with clang

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Date:   Thu, 7 May 2020 12:21:10 +0200
From:   Miquel Raynal <miquel.raynal@...tlin.com>
To:     Nathan Chancellor <natechancellor@...il.com>
Cc:     Arnd Bergmann <arnd@...db.de>, Richard Weinberger <richard@....at>,
        Vignesh Raghavendra <vigneshr@...com>,
        Vincenzo Aliberti <vincenzo.aliberti@...il.com>,
        Brian Norris <computersforpeace@...il.com>,
        Richard Fontana <rfontana@...hat.com>,
        linux-mtd@...ts.infradead.org, linux-kernel@...r.kernel.org,
        clang-built-linux@...glegroups.com
Subject: Re: [PATCH] mtd: lpddr: fix excessive stack usage with clang


Nathan Chancellor <natechancellor@...il.com> wrote on Tue, 5 May 2020
19:38:28 -0700:

> On Tue, May 05, 2020 at 04:01:16PM +0200, Arnd Bergmann wrote:
> > Building lpddr2_nvm with clang can result in a giant stack usage
> > in one function:
> > 
> > drivers/mtd/lpddr/lpddr2_nvm.c:399:12: error: stack frame size of 1144 bytes in function 'lpddr2_nvm_probe' [-Werror,-Wframe-larger-than=]
> > 
> > The problem is that clang decides to build a copy of the mtd_info
> > structure on the stack and then do a memcpy() into the actual version. It
> > shouldn't really do it that way, but it's not strictly a bug either.
> > 
> > As a workaround, use a static const version of the structure to assign
> > most of the members upfront and then only set the few members that
> > require runtime knowledge at probe time.
> > 
> > Fixes: 96ba9dd65788 ("mtd: lpddr: add driver for LPDDR2-NVM PCM memories")
> > Signed-off-by: Arnd Bergmann <arnd@...db.de>  
> 
> Reviewed-by: Nathan Chancellor <natechancellor@...il.com>

Acked-by: Miquel Raynal <miquel.raynal@...tlin.com>

> 
> > ---
> >  drivers/mtd/lpddr/lpddr2_nvm.c | 35 ++++++++++++++++++----------------
> >  1 file changed, 19 insertions(+), 16 deletions(-)
> > 
> > diff --git a/drivers/mtd/lpddr/lpddr2_nvm.c b/drivers/mtd/lpddr/lpddr2_nvm.c
> > index 0f1547f09d08..72f5c7b30079 100644
> > --- a/drivers/mtd/lpddr/lpddr2_nvm.c
> > +++ b/drivers/mtd/lpddr/lpddr2_nvm.c
> > @@ -393,6 +393,17 @@ static int lpddr2_nvm_lock(struct mtd_info *mtd, loff_t start_add,
> >  	return lpddr2_nvm_do_block_op(mtd, start_add, len, LPDDR2_NVM_LOCK);
> >  }
> >  
> > +static const struct mtd_info lpddr2_nvm_mtd_info = {
> > +	.type		= MTD_RAM,
> > +	.writesize	= 1,
> > +	.flags		= (MTD_CAP_NVRAM | MTD_POWERUP_LOCK),
> > +	._read		= lpddr2_nvm_read,
> > +	._write		= lpddr2_nvm_write,
> > +	._erase		= lpddr2_nvm_erase,
> > +	._unlock	= lpddr2_nvm_unlock,
> > +	._lock		= lpddr2_nvm_lock,
> > +};
> > +
> >  /*
> >   * lpddr2_nvm driver probe method
> >   */
> > @@ -433,6 +444,7 @@ static int lpddr2_nvm_probe(struct platform_device *pdev)
> >  		.pfow_base	= OW_BASE_ADDRESS,
> >  		.fldrv_priv	= pcm_data,
> >  	};
> > +
> >  	if (IS_ERR(map->virt))
> >  		return PTR_ERR(map->virt);
> >  
> > @@ -444,22 +456,13 @@ static int lpddr2_nvm_probe(struct platform_device *pdev)
> >  		return PTR_ERR(pcm_data->ctl_regs);
> >  
> >  	/* Populate mtd_info data structure */
> > -	*mtd = (struct mtd_info) {
> > -		.dev		= { .parent = &pdev->dev },
> > -		.name		= pdev->dev.init_name,
> > -		.type		= MTD_RAM,
> > -		.priv		= map,
> > -		.size		= resource_size(add_range),
> > -		.erasesize	= ERASE_BLOCKSIZE * pcm_data->bus_width,
> > -		.writesize	= 1,
> > -		.writebufsize	= WRITE_BUFFSIZE * pcm_data->bus_width,
> > -		.flags		= (MTD_CAP_NVRAM | MTD_POWERUP_LOCK),
> > -		._read		= lpddr2_nvm_read,
> > -		._write		= lpddr2_nvm_write,
> > -		._erase		= lpddr2_nvm_erase,
> > -		._unlock	= lpddr2_nvm_unlock,
> > -		._lock		= lpddr2_nvm_lock,
> > -	};
> > +	*mtd = lpddr2_nvm_mtd_info;
> > +	mtd->dev.parent		= &pdev->dev;
> > +	mtd->name		= pdev->dev.init_name;
> > +	mtd->priv		= map;
> > +	mtd->size		= resource_size(add_range);
> > +	mtd->erasesize		= ERASE_BLOCKSIZE * pcm_data->bus_width;
> > +	mtd->writebufsize	= WRITE_BUFFSIZE * pcm_data->bus_width;
> >  
> >  	/* Verify the presence of the device looking for PFOW string */
> >  	if (!lpddr2_nvm_pfow_present(map)) {
> > -- 
> > 2.26.0
> >