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

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Message-Id: <20250122065031.1321015-1-arnd@kernel.org>
Date: Wed, 22 Jan 2025 07:50:26 +0100
From: Arnd Bergmann <arnd@...nel.org>
To: Jason Baron <jbaron@...mai.com>,
	Borislav Petkov <bp@...en8.de>,
	Tony Luck <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-kernel@...r.kernel.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 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 */
 	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