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Date: Fri, 11 Apr 2025 14:29:27 +0200
From: Greg KH <gregkh@linuxfoundation.org>
To: Purva Yeshi <purvayeshi550@gmail.com>
Cc: jirislaby@kernel.org, andriy.shevchenko@linux.intel.com,
	arnd@kernel.org, cang1@live.co.uk, bhelgaas@google.com,
	linux-kernel@vger.kernel.org, linux-serial@vger.kernel.org
Subject: Re: [PATCH] tty: serial: 8250: Fix uninitialized variable warnings
 in pci_oxsemi_tornado_get_divisor
Message-ID: <2025041110-simmering-bogus-7a1d@gregkh>
References: <20250411115048.34948-1-purvayeshi550@gmail.com>
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In-Reply-To: <20250411115048.34948-1-purvayeshi550@gmail.com>

On Fri, Apr 11, 2025 at 05:20:48PM +0530, Purva Yeshi wrote:
> Fix Smatch-detected issue:
> 
> drivers/tty/serial/8250/8250_pci.c:1233 pci_oxsemi_tornado_get_divisor()
> error: uninitialized symbol 'tcr'.
> drivers/tty/serial/8250/8250_pci.c:1234 pci_oxsemi_tornado_get_divisor()
> error: uninitialized symbol 'quot'.
> drivers/tty/serial/8250/8250_pci.c:1238 pci_oxsemi_tornado_get_divisor()
> error: uninitialized symbol 'quot'.
> drivers/tty/serial/8250/8250_pci.c:1242 pci_oxsemi_tornado_get_divisor()
> error: uninitialized symbol 'cpr'.
> drivers/tty/serial/8250/8250_pci.c:1252 pci_oxsemi_tornado_get_divisor()
> error: uninitialized symbol 'cpr'.
> 
> Fix uninitialized variable usage in pci_oxsemi_tornado_get_divisor() that
> was triggering sparse warnings and potential undefined behavior. The
> variables tcr, cpr, and quot were used before being explicitly assigned
> values, leading to smatch warning in multiple lines of the function.

Are you really sure?  If you follow through the logic, it looks fine to
me.  What am I missing?  And why doesn't gcc or clang catch this?

> Initialize quot to 1, tcr to 16, and cpr to OXSEMI_TORNADO_CPR_DEF at the
> point of declaration. This ensures safe fallback values are used when these
> variables are not conditionally set later in the function, avoiding
> uninitialized access.

Where did these magic values come from?

thanks,

greg k-h