linux-kernel - Re: [PATCH v1 0/4] [RFC] Implement Trampoline File Descriptor

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Message-ID: <5f3c9616-52f5-f539-a39f-3fd3ada4f0aa@linux.microsoft.com>
Date:   Tue, 4 Aug 2020 09:48:11 -0500
From:   "Madhavan T. Venkataraman" <madvenka@...ux.microsoft.com>
To:     David Laight <David.Laight@...LAB.COM>,
        'Mark Rutland' <mark.rutland@....com>
Cc:     Andy Lutomirski <luto@...nel.org>,
        Kernel Hardening <kernel-hardening@...ts.openwall.com>,
        Linux API <linux-api@...r.kernel.org>,
        linux-arm-kernel <linux-arm-kernel@...ts.infradead.org>,
        Linux FS Devel <linux-fsdevel@...r.kernel.org>,
        linux-integrity <linux-integrity@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        LSM List <linux-security-module@...r.kernel.org>,
        Oleg Nesterov <oleg@...hat.com>, X86 ML <x86@...nel.org>
Subject: Re: [PATCH v1 0/4] [RFC] Implement Trampoline File Descriptor



On 8/4/20 9:33 AM, David Laight wrote:
>>> If you look at the libffi reference patch I have included, the architecture
>>> specific changes to use trampfd just involve a single C function call to
>>> a common code function.
> No idea what libffi is, but it must surely be simpler to
> rewrite it to avoid nested function definitions.

Sorry if I wasn't clear.

libffi is a separate use case and GCC nested functions is a separate one.
libffi is not used to solve the nested function stuff.

For nested functions, GCC generates trampoline code and arranges to
place it on the stack and execute it.

I agree with your other points about nested function implementation.

Madhavan
> Or find a book from the 1960s on how to do recursive
> calls and nested functions in FORTRAN-IV.
>
> 	David
>
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