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Message-ID: <5a6ad008-61c6-4f65-82b3-a4e538cbb9e8@akamai.com>
Date: Fri, 24 Jan 2025 14:27:53 -0500
From: Jason Baron <jbaron@...mai.com>
To: "Zhuo, Qiuxu" <qiuxu.zhuo@...el.com>, Arnd Bergmann <arnd@...nel.org>,
        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



On 1/22/25 9:18 AM, Zhuo, Qiuxu wrote:
> !-------------------------------------------------------------------|
>    This Message Is From an External Sender
>    This message came from outside your organization.
> |-------------------------------------------------------------------!
> 
>> 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>

Seems fine with the comment adjustment.

Thanks.

Acked-by: Jason Baron <jbaron@...mai.com>


>> ---
>>   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
>>
> 

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