linux-kernel - Re: [PATCH] PCI: Fix BUILD_BUG

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Message-ID: <20250210220010.GM32480@redhat.com>
Date: Mon, 10 Feb 2025 23:00:11 +0100
From: Oleg Nesterov <oleg@...hat.com>
To: Alex Williamson <alex.williamson@...hat.com>
Cc: bhelgaas@...gle.com, linux-pci@...r.kernel.org,
	linux-kernel@...r.kernel.org, mitchell.augustin@...onical.com,
	ilpo.jarvinen@...ux.intel.com
Subject: Re: [PATCH] PCI: Fix BUILD_BUG_ON usage for old gcc

On 02/10, Alex Williamson wrote:
>
> 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>
  ^^^^^^^^^^^^

Well, thanks, but I didn't ;)

> @@ -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);

Thanks!

Tested-by: Oleg Nesterov <oleg@...hat.com>