linux-kernel - Re: [PATCH] staging: vchiq: add 'static' to function definition

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Message-Id: <52599d6e-dc16-4186-9fb9-d17ce428fe9c@app.fastmail.com>
Date:   Thu, 27 Oct 2022 16:08:22 +0200
From:   "Arnd Bergmann" <arnd@...db.de>
To:     "Greg Kroah-Hartman" <gregkh@...uxfoundation.org>,
        "Scott J. Crouch" <scottjcrouch@...il.com>
Cc:     "Florian Fainelli" <f.fainelli@...il.com>,
        "Broadcom internal kernel review list" 
        <bcm-kernel-feedback-list@...adcom.com>,
        kernel-janitors@...r.kernel.org,
        linux-rpi-kernel@...ts.infradead.org,
        linux-arm-kernel@...ts.infradead.org,
        linux-staging@...ts.linux.dev, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] staging: vchiq: add 'static' to function definition

On Sat, Oct 22, 2022, at 10:07, Greg Kroah-Hartman wrote:
> On Sat, Oct 22, 2022 at 03:35:48PM +1100, Scott J. Crouch wrote:

> Nice try, but this breaks the build in a very horrible and strange way
> that no one has been able to figure out yet:

I got curious and figured out what happens:

Without CONFIG_OF, of_match_node() always returns NULL, so
vchiq_probe() returns -EINVAL unconditionally before calling
vchiq_platform_init(). 

If vchiq_platform_init() is marked 'static', gcc's dead code
elimination then eliminates it, which in turn means that
'g_fragments_base' is never initialized and gets replaced
with a NULL pointer.

I think the easiest workaround is to take this otherwise correct
patch but at the same time add 'depends on OF' to BCM2835_VCHIQ.
This is a correct dependency as shown by gcc above, and it still
allows compile testing this driver on x86 allmodconfig, which
enables CONFIG_OF.

     Arnd