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Date:   Wed, 18 Nov 2020 15:02:36 -0500
From:   Steven Rostedt <rostedt@goodmis.org>
To:     Alexei Starovoitov <alexei.starovoitov@gmail.com>
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
Subject: Re: violating function pointer signature
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On Wed, 18 Nov 2020 11:46:02 -0800
Alexei Starovoitov <alexei.starovoitov@gmail.com> wrote:

> 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.

I also said that this is limited to only functions that have void return.

-- Steve