linux-kernel - Re: [PATCH] net: mdio: fix -Wvoid-pointer-to-enum-cast warning

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Message-ID: <ZNycLZCK4GGfayWg@shell.armlinux.org.uk>
Date:   Wed, 16 Aug 2023 10:51:41 +0100
From:   "Russell King (Oracle)" <linux@...linux.org.uk>
To:     Andrew Lunn <andrew@...n.ch>
Cc:     Justin Stitt <justinstitt@...gle.com>,
        Iyappan Subramanian <iyappan@...amperecomputing.com>,
        Keyur Chudgar <keyur@...amperecomputing.com>,
        Quan Nguyen <quan@...amperecomputing.com>,
        Heiner Kallweit <hkallweit1@...il.com>,
        "David S. Miller" <davem@...emloft.net>,
        Eric Dumazet <edumazet@...gle.com>,
        Jakub Kicinski <kuba@...nel.org>,
        Paolo Abeni <pabeni@...hat.com>,
        Nathan Chancellor <nathan@...nel.org>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        Tom Rix <trix@...hat.com>, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org, llvm@...ts.linux.dev
Subject: Re: [PATCH] net: mdio: fix -Wvoid-pointer-to-enum-cast warning

On Tue, Aug 15, 2023 at 10:41:39PM +0200, Andrew Lunn wrote:
> On Tue, Aug 15, 2023 at 08:35:59PM +0000, Justin Stitt wrote:
> > When building with clang 18 I see the following warning:
> > |       drivers/net/mdio/mdio-xgene.c:338:13: warning: cast to smaller integer
> > |               type 'enum xgene_mdio_id' from 'const void *' [-Wvoid-pointer-to-enum-cast]
> > |         338 |                 mdio_id = (enum xgene_mdio_id)of_id->data;
> > 
> > This is due to the fact that `of_id->data` is a void* while `enum
> > xgene_mdio_id` has the size of an int. This leads to truncation and
> > possible data loss.
> > 
> > Link: https://github.com/ClangBuiltLinux/linux/issues/1910
> > Reported-by: Nathan Chancellor <nathan@...nel.org>
> > Signed-off-by: Justin Stitt <justinstitt@...gle.com>
> 
> Reviewed-by: Andrew Lunn <andrew@...n.ch>

I wonder whether it would be better to use device_get_match_data()
here? The whole of_match_device()...acpi_match_device() dance could
become:

+	mdio_id = (uintptr_t)device_get_match_data(&pdev->dev);
	if (!mdio_id)
		return -ENODEV;

It's probably something for a follow-up patch though.

Reviewed-by: Russell King (Oracle) <rmk+kernel@...linux.org.uk>

Thanks!

-- 
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