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From:   Florian Weimer <fw@deneb.enyo.de>
To:     Peter Zijlstra <peterz@infradead.org>
Cc:     Steven Rostedt <rostedt@goodmis.org>,
        Mathieu Desnoyers <mathieu.desnoyers@efficios.com>,
        linux-kernel <linux-kernel@vger.kernel.org>,
        Matt Mullins <mmullins@mmlx.us>,
        Ingo Molnar <mingo@redhat.com>,
        Alexei Starovoitov <ast@kernel.org>,
        Daniel Borkmann <daniel@iogearbox.net>,
        Dmitry Vyukov <dvyukov@google.com>,
        Martin KaFai Lau <kafai@fb.com>,
        Song Liu <songliubraving@fb.com>, Yonghong Song <yhs@fb.com>,
        Andrii Nakryiko <andriin@fb.com>,
        John Fastabend <john.fastabend@gmail.com>,
        KP Singh <kpsingh@chromium.org>,
        netdev <netdev@vger.kernel.org>, bpf <bpf@vger.kernel.org>,
        Kees Cook <keescook@chromium.org>,
        Josh Poimboeuf <jpoimboe@redhat.com>,
        linux-toolchains@vger.kernel.org
Subject: Re: violating function pointer signature
References: <20201116175107.02db396d@gandalf.local.home>
        <47463878.48157.1605640510560.JavaMail.zimbra@efficios.com>
        <20201117142145.43194f1a@gandalf.local.home>
        <375636043.48251.1605642440621.JavaMail.zimbra@efficios.com>
        <20201117153451.3015c5c9@gandalf.local.home>
        <20201118132136.GJ3121378@hirez.programming.kicks-ass.net>
        <87h7pmwyta.fsf@mid.deneb.enyo.de>
        <20201118141226.GV3121392@hirez.programming.kicks-ass.net>
Date:   Wed, 18 Nov 2020 15:18:29 +0100
In-Reply-To: <20201118141226.GV3121392@hirez.programming.kicks-ass.net> (Peter
        Zijlstra's message of "Wed, 18 Nov 2020 15:12:26 +0100")
Message-ID: <874klmwxxm.fsf@mid.deneb.enyo.de>
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* Peter Zijlstra:

>> The default Linux calling conventions are all of the cdecl family,
>> where the caller pops the argument off the stack.  You didn't quote
>> enough to context to tell whether other calling conventions matter in
>> your case.
>
> This is strictly in-kernel, and I think we're all cdecl, of which the
> important part is caller-cleanup. The function compiles to:
>
> 	RET
>
> so whatever the arguments are is irrelevant.

Yes, then the stub is ABI-compatible, as far as I know.