linux-kernel - RE: [PATCH] EDAC/ie31200: work around false positive build warning

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Message-ID: <CY8PR11MB7134E3B1BE3DC6448EEF36A289E12@CY8PR11MB7134.namprd11.prod.outlook.com>
Date: Wed, 22 Jan 2025 14:18:33 +0000
From: "Zhuo, Qiuxu" <qiuxu.zhuo@...el.com>
To: Arnd Bergmann <arnd@...nel.org>, Jason Baron <jbaron@...mai.com>, Borislav
 Petkov <bp@...en8.de>, "Luck, Tony" <tony.luck@...el.com>
CC: Arnd Bergmann <arnd@...db.de>, James Morse <james.morse@....com>, "Mauro
 Carvalho Chehab" <mchehab@...nel.org>, Robert Richter <rric@...nel.org>,
	James Ye <jye836@...il.com>, "linux-edac@...r.kernel.org"
	<linux-edac@...r.kernel.org>, "linux-kernel@...r.kernel.org"
	<linux-kernel@...r.kernel.org>
Subject: RE: [PATCH] EDAC/ie31200: work around false positive build warning

> From: Arnd Bergmann <arnd@...nel.org>
> [...]
> Subject: [PATCH] EDAC/ie31200: work around false positive build warning
> 
> From: Arnd Bergmann <arnd@...db.de>
> 
> gcc-14 produces a bogus warning in some configurations:
> 
> drivers/edac/ie31200_edac.c: In function 'ie31200_probe1.isra':
> drivers/edac/ie31200_edac.c:412:26: error: 'dimm_info' is used uninitialized
> [-Werror=uninitialized]
>   412 |         struct dimm_data
> dimm_info[IE31200_CHANNELS][IE31200_DIMMS_PER_CHANNEL];
>       |                          ^~~~~~~~~
> drivers/edac/ie31200_edac.c:412:26: note: 'dimm_info' declared here
>   412 |         struct dimm_data
> dimm_info[IE31200_CHANNELS][IE31200_DIMMS_PER_CHANNEL];
>       |                          ^~~~~~~~~
> 
> I don't see any way the unintialized access could really happen here, but I can

It looks like gcc-14 isn't smart enough to recognize that this is a false positive build warning :-).
Actually, the dim_info[][] array is always initialized by populate_dimm_info().

> see why the compiler gets confused by the two loops.
> 
> Instead, rework the two nested loops to only read the addr_decode registers
> and then keep only one instance of the dimm info structure.
> 
> Signed-off-by: Arnd Bergmann <arnd@...db.de>
> ---
>  drivers/edac/ie31200_edac.c | 27 +++++++++++++--------------
>  1 file changed, 13 insertions(+), 14 deletions(-)
> 
> diff --git a/drivers/edac/ie31200_edac.c b/drivers/edac/ie31200_edac.c index
> 4fc16922dc1a..b0ccc54dc66a 100644
> --- a/drivers/edac/ie31200_edac.c
> +++ b/drivers/edac/ie31200_edac.c
> @@ -409,10 +409,9 @@ static int ie31200_probe1(struct pci_dev *pdev, int
> dev_idx)
>  	int i, j, ret;
>  	struct mem_ctl_info *mci = NULL;
>  	struct edac_mc_layer layers[2];
> -	struct dimm_data
> dimm_info[IE31200_CHANNELS][IE31200_DIMMS_PER_CHANNEL];
>  	void __iomem *window;
>  	struct ie31200_priv *priv;
> -	u32 addr_decode, mad_offset;
> +	u32 addr_decode[IE31200_CHANNELS], mad_offset;
> 
>  	/*
>  	 * Kaby Lake, Coffee Lake seem to work like Skylake. Please re-visit
> @@ -472,17 +471,9 @@ static int ie31200_probe1(struct pci_dev *pdev, int
> dev_idx)
> 
>  	/* populate DIMM info */

This comment also needs to be moved to just above the new location of populate_dimm_info().

>  	for (i = 0; i < IE31200_CHANNELS; i++) {
> -		addr_decode = readl(window + mad_offset +
> +		addr_decode[i] = readl(window + mad_offset +
>  					(i * 4));
> -		edac_dbg(0, "addr_decode: 0x%x\n", addr_decode);
> -		for (j = 0; j < IE31200_DIMMS_PER_CHANNEL; j++) {
> -			populate_dimm_info(&dimm_info[i][j], addr_decode,
> j,
> -					   skl);
> -			edac_dbg(0, "size: 0x%x, rank: %d, width: %d\n",
> -				 dimm_info[i][j].size,
> -				 dimm_info[i][j].dual_rank,
> -				 dimm_info[i][j].x16_width);
> -		}
> +		edac_dbg(0, "addr_decode: 0x%x\n", addr_decode[i]);
>  	}
> 
>  	/*
> @@ -493,14 +484,22 @@ static int ie31200_probe1(struct pci_dev *pdev, int
> dev_idx)
>  	 */
>  	for (i = 0; i < IE31200_DIMMS_PER_CHANNEL; i++) {
>  		for (j = 0; j < IE31200_CHANNELS; j++) {
> +			struct dimm_data dimm_info;
>  			struct dimm_info *dimm;
>  			unsigned long nr_pages;
> 
> -			nr_pages = IE31200_PAGES(dimm_info[j][i].size, skl);

Move the comment here.

> +			populate_dimm_info(&dimm_info, addr_decode[j], i,
> +					   skl);
> +			edac_dbg(0, "size: 0x%x, rank: %d, width: %d\n",
> +				 dimm_info.size,
> +				 dimm_info.dual_rank,
> +				 dimm_info.x16_width);
> +
> +			nr_pages = IE31200_PAGES(dimm_info.size, skl);
>  			if (nr_pages == 0)
>  				continue;
> 
> -			if (dimm_info[j][i].dual_rank) {
> +			if (dimm_info.dual_rank) {
>  				nr_pages = nr_pages / 2;
>  				dimm = edac_get_dimm(mci, (i * 2) + 1, j, 0);
>  				dimm->nr_pages = nr_pages;
> --
> 2.39.5
>