linux-kernel - [PATCH] PCI: Fix BUILD_BUG

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Message-ID: <20250210210109.3673582-1-alex.williamson@redhat.com>
Date: Mon, 10 Feb 2025 14:01:04 -0700
From: Alex Williamson <alex.williamson@...hat.com>
To: bhelgaas@...gle.com
Cc: Alex Williamson <alex.williamson@...hat.com>,
	linux-pci@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	mitchell.augustin@...onical.com,
	ilpo.jarvinen@...ux.intel.com,
	Oleg Nesterov <oleg@...hat.com>
Subject: [PATCH] PCI: Fix BUILD_BUG_ON usage for old gcc

As reported in the below link, it seems older versions of gcc cannot
determine that the howmany variable is known for all callers.  Include
a test so that newer compilers can still enforce this sanity check and
older compilers can still work.

Fixes: 4453f360862e ("PCI: Batch BAR sizing operations")
Link: https://lore.kernel.org/all/20250209154512.GA18688@redhat.com
Reported-by: Oleg Nesterov <oleg@...hat.com>
Suggested-by: Oleg Nesterov <oleg@...hat.com>
Signed-off-by: Alex Williamson <alex.williamson@...hat.com>
---

Verified against gcc 14.2.1 to still trigger a build error if called
with a constant value greater than 6, Oleg to confirm build issue is
resolved for gcc 5.3.1.

 drivers/pci/probe.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/drivers/pci/probe.c b/drivers/pci/probe.c
index b6536ed599c3..1bde89d0dc0d 100644
--- a/drivers/pci/probe.c
+++ b/drivers/pci/probe.c
@@ -345,7 +345,8 @@ static void pci_read_bases(struct pci_dev *dev, unsigned int howmany, int rom)
 	unsigned int pos, reg;
 	u16 orig_cmd;
 
-	BUILD_BUG_ON(howmany > PCI_STD_NUM_BARS);
+	BUILD_BUG_ON(__builtin_constant_p(howmany) &&
+		     howmany > PCI_STD_NUM_BARS);
 
 	if (dev->non_compliant_bars)
 		return;
-- 
2.47.1