linux-kernel - Re: module version magic and arches with symbol prefixes

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Message-Id: <200906191508.06537.rusty@rustcorp.com.au>
Date:	Fri, 19 Jun 2009 15:08:05 +0930
From:	Rusty Russell <rusty@...tcorp.com.au>
To:	Mike Frysinger <vapier.adi@...il.com>
Cc:	Linux kernel mailing list <linux-kernel@...r.kernel.org>,
	Robin Getz <rgetz@...ckfin.uclinux.org>
Subject: Re: module version magic and arches with symbol prefixes

On Fri, 19 Jun 2009 12:54:44 am Mike Frysinger wrote:
> the current check_modstruct_version() does this:
> {
>     const unsigned long *crc;
>
>     if (!find_symbol("module_layout", NULL, &crc, true, false))
>         BUG();
>     return check_version(sechdrs, versindex, "module_layout", mod, crc);
> }
> the trouble here is that it looks for a literal "module_layout" symbol
> and for ports that have symbol prefixes (a quick check shows Blackfin
> & h8300), this aint going to work.

MODULE_SYMBOL_PREFIX is the fix for this, ie:

	if (!find_symbol(MODULE_SYMBOL_PREFIX "module_layout), ...

> also, using BUG() here seems pretty damn harsh.  wouldnt it make more
> sense to do something like:
>     if (WARN_ON(!find_symbol("module_layout", NULL, &crc, true, false)))
>         return 0;
> this way the module is simply not loaded rather than killing the kernel

No, it means the kernel didn't build properly.  Better to fail spectacularly: 
ideally we'd do this find in an init routine and guarantee a boot crash.

Thanks,
Rusty.
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