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[PATCH] EDAC/ie31200: work around false positive build warning

Arnd Bergmann posted 1 patch 11 months ago 
drivers/edac/ie31200_edac.c | 27 +++++++++++++--------------
1 file changed, 13 insertions(+), 14 deletions(-)
[PATCH] EDAC/ie31200: work around false positive build warning
Posted by Arnd Bergmann 11 months ago 
From: Arnd Bergmann <arnd@arndb.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 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@arndb.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 */
 	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);
+			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
RE: [PATCH] EDAC/ie31200: work around false positive build warning
Posted by Zhuo, Qiuxu 11 months ago 
> From: Arnd Bergmann <arnd@kernel.org>
> [...]
> Subject: [PATCH] EDAC/ie31200: work around false positive build warning
> 
> From: Arnd Bergmann <arnd@arndb.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@arndb.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
>
Re: [PATCH] EDAC/ie31200: work around false positive build warning
Posted by Jason Baron 10 months, 4 weeks ago 

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@kernel.org>
>> [...]
>> Subject: [PATCH] EDAC/ie31200: work around false positive build warning
>>
>> From: Arnd Bergmann <arnd@arndb.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@arndb.de>

Seems fine with the comment adjustment.

Thanks.

Acked-by: Jason Baron <jbaron@akamai.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
>>
>
Re: [PATCH] EDAC/ie31200: work around false positive build warning
Posted by Luck, Tony 10 months ago 
> > 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@arndb.de>
> 
> Seems fine with the comment adjustment.
> 
> Thanks.
> 
> Acked-by: Jason Baron <jbaron@akamai.com>

Applied (with comment adjustment) to RAS tree edac-drivers branch

Thanks

-Tony

Patchew 2.1-devel-b67e4c2

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