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Date: Wed, 16 Jul 2025 07:06:50 +0200
From: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
To: Nathan Chancellor <nathan@kernel.org>
Cc: accessrunner-general@lists.sourceforge.net, linux-usb@vger.kernel.org,
	llvm@lists.linux.dev, patches@lists.linux.dev,
	stable@vger.kernel.org
Subject: Re: [PATCH] usb: atm: cxacru: Zero initialize bp in
 cxacru_heavy_init()
Message-ID: <2025071618-jester-outing-7fed@gregkh>
References: <20250715-usb-cxacru-fix-clang-21-uninit-warning-v1-1-de6c652c3079@kernel.org>
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In-Reply-To: <20250715-usb-cxacru-fix-clang-21-uninit-warning-v1-1-de6c652c3079@kernel.org>

On Tue, Jul 15, 2025 at 01:33:32PM -0700, Nathan Chancellor wrote:
> After a recent change in clang to expose uninitialized warnings from
> const variables [1], there is a warning in cxacru_heavy_init():
> 
>   drivers/usb/atm/cxacru.c:1104:6: error: variable 'bp' is used uninitialized whenever 'if' condition is false [-Werror,-Wsometimes-uninitialized]
>    1104 |         if (instance->modem_type->boot_rom_patch) {
>         |             ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
>   drivers/usb/atm/cxacru.c:1113:39: note: uninitialized use occurs here
>    1113 |         cxacru_upload_firmware(instance, fw, bp);
>         |                                              ^~
>   drivers/usb/atm/cxacru.c:1104:2: note: remove the 'if' if its condition is always true
>    1104 |         if (instance->modem_type->boot_rom_patch) {
>         |         ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
>   drivers/usb/atm/cxacru.c:1095:32: note: initialize the variable 'bp' to silence this warning
>    1095 |         const struct firmware *fw, *bp;
>         |                                       ^
>         |                                        = NULL
> 
> This warning occurs in clang's frontend before inlining occurs, so it
> cannot notice that bp is only used within cxacru_upload_firmware() under
> the same condition that initializes it in cxacru_heavy_init(). Just
> initialize bp to NULL to silence the warning without functionally
> changing the code, which is what happens with modern compilers when they
> support '-ftrivial-auto-var-init=zero' (CONFIG_INIT_STACK_ALL_ZERO=y).

We generally do not want to paper over compiler bugs, when our code is
correct, so why should we do that here?  Why not fix clang instead?

thanks,

greg k-h