linux-kernel - Re: [EXTERNAL][PATCH 1/5] PCI: Convert pci_resource_to

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Date:   Sun, 28 Jul 2019 22:49:55 +0000
From:   Paul Burton <paul.burton@...s.com>
To:     Denis Efremov <efremov@...ux.com>
CC:     Bjorn Helgaas <bhelgaas@...gle.com>,
        "David S. Miller" <davem@...emloft.net>,
        Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Paul Mackerras <paulus@...ba.org>,
        Michael Ellerman <mpe@...erman.id.au>,
        Ralf Baechle <ralf@...ux-mips.org>,
        James Hogan <jhogan@...nel.org>,
        Michal Simek <monstr@...str.eu>,
        "linux-mips@...r.kernel.org" <linux-mips@...r.kernel.org>,
        "linuxppc-dev@...ts.ozlabs.org" <linuxppc-dev@...ts.ozlabs.org>,
        "sparclinux@...r.kernel.org" <sparclinux@...r.kernel.org>,
        "linux-pci@...r.kernel.org" <linux-pci@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [EXTERNAL][PATCH 1/5] PCI: Convert pci_resource_to_user to a weak
 function

Hi Denis,

On Sun, Jul 28, 2019 at 11:22:09PM +0300, Denis Efremov wrote:
> diff --git a/include/linux/pci.h b/include/linux/pci.h
> index 9e700d9f9f28..1a19d0151b0a 100644
> --- a/include/linux/pci.h
> +++ b/include/linux/pci.h
> @@ -1870,25 +1870,13 @@ static inline const char *pci_name(const struct pci_dev *pdev)
>  	return dev_name(&pdev->dev);
>  }
>  
> -
>  /*
>   * Some archs don't want to expose struct resource to userland as-is
>   * in sysfs and /proc
>   */
> -#ifdef HAVE_ARCH_PCI_RESOURCE_TO_USER
> -void pci_resource_to_user(const struct pci_dev *dev, int bar,
> -			  const struct resource *rsrc,
> -			  resource_size_t *start, resource_size_t *end);
> -#else
> -static inline void pci_resource_to_user(const struct pci_dev *dev, int bar,
> -		const struct resource *rsrc, resource_size_t *start,
> -		resource_size_t *end)
> -{
> -	*start = rsrc->start;
> -	*end = rsrc->end;
> -}
> -#endif /* HAVE_ARCH_PCI_RESOURCE_TO_USER */
> -
> +void __weak pci_resource_to_user(const struct pci_dev *dev, int bar,
> +				 const struct resource *rsrc,
> +				 resource_size_t *start, resource_size_t *end);
>  
>  /*
>   * The world is not perfect and supplies us with broken PCI devices.

This is wrong - using __weak on the declaration in a header will cause
the weak attribute to be applied to all implementations too (presuming
the C files containing the implementations include the header). You then
get whichever impleentation the linker chooses, which isn't necessarily
the one you wanted.

checkpatch.pl should produce an error about this - see the
WEAK_DECLARATION error introduced in commit 619a908aa334 ("checkpatch:
add error on use of attribute((weak)) or __weak declarations").

Thanks,
    Paul