linux-kernel - Re: [PATCH v2 0/2] Lock and Pointer guards

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Date:   Tue, 6 Jun 2023 09:06:40 -0700
From:   Kees Cook <keescook@...omium.org>
To:     Linus Torvalds <torvalds@...ux-foundation.org>
Cc:     Peter Zijlstra <peterz@...radead.org>, gregkh@...uxfoundation.org,
        pbonzini@...hat.com, linux-kernel@...r.kernel.org,
        ojeda@...nel.org, ndesaulniers@...gle.com, mingo@...hat.com,
        will@...nel.org, longman@...hat.com, boqun.feng@...il.com,
        juri.lelli@...hat.com, vincent.guittot@...aro.org,
        dietmar.eggemann@....com, rostedt@...dmis.org, bsegall@...gle.com,
        mgorman@...e.de, bristot@...hat.com, vschneid@...hat.com,
        paulmck@...nel.org, frederic@...nel.org, quic_neeraju@...cinc.com,
        joel@...lfernandes.org, josh@...htriplett.org,
        mathieu.desnoyers@...icios.com, jiangshanlai@...il.com,
        rcu@...r.kernel.org, tj@...nel.org, tglx@...utronix.de,
        linux-toolchains@...r.kernel.org
Subject: Re: [PATCH v2 0/2] Lock and Pointer guards

On Tue, Jun 06, 2023 at 07:50:47AM -0700, Linus Torvalds wrote:
> So you could have something like
> 
>   #define RAII(type, var, init, exit) \
>         __RAII(type, var, init, exit, __UNIQUE_ID(fn)
> 
>   #define __RAII(type, var, init, exit, exitname) \
>         void exitname(type *p) { exit } \
>         type var __attribute__((__cleanup__(exitname))) = (init)
> 
> and do all of the above with
> 
>     RAII(struct fd, fd, fdget(f), fdput(fd));

"fdput(fd)" needs to be "fdput(*p)", since otherwise "fdput(fd)" is
referencing "fd" before it has been declared.

But regardless, yes, Clang is angry about the nested function. Also,
while my toy[1] example doesn't show it, GCC may also generate code
that requires an executable stack for some instances (or at least it
did historically) that need trampolines.

[1] https://godbolt.org/z/WTjx6Gs7x

Also, more nits on naming: isn't this more accurately called Scope-based
Resource Management (SBRM) not RAII? (RAII is technically object lifetime,
and SBRM is scope entry/exit.)

-- 
Kees Cook