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From:   Alexei Starovoitov <alexei.starovoitov@gmail.com>
Date:   Wed, 18 Nov 2020 11:46:02 -0800
Message-ID: <CAADnVQLv2pnw1x66Y_cYmdBg=sF+7s31VVoEmSerDnbuR0pU_g@mail.gmail.com>
Subject: Re: violating function pointer signature
To:     Steven Rostedt <rostedt@goodmis.org>
Cc:     Florian Weimer <fw@deneb.enyo.de>,
        Peter Zijlstra <peterz@infradead.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
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On Wed, Nov 18, 2020 at 6:22 AM Steven Rostedt <rostedt@goodmis.org> wrote:
>
> Thus, all functions will be non-variadic in these cases.

That's not the only case where it will blow up.
Try this on sparc:
struct foo {
int a;
};

struct foo foo_struct(void) {
struct foo f = {};
return f;
}
int foo_int(void) {
return 0;
}
or this link:
https://godbolt.org/z/EdM47b

Notice:
jmp %i7+12
The function that returns small struct will jump to a different
instruction in the caller.

I think none of the tracepoints return structs and void foo(void) is
fine on x86.
Just pointing out that it's more than just variadic.