Re: violating function pointer signature

From: Alexei Starovoitov <alexei.starovoitov@gmail.com>
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
Subject: Re: violating function pointer signature
Date: Wed, 18 Nov 2020 11:46:02 -0800	[thread overview]
Message-ID: <CAADnVQLv2pnw1x66Y_cYmdBg=sF+7s31VVoEmSerDnbuR0pU_g@mail.gmail.com> (raw)
In-Reply-To: <20201118092228.4f6e5930@gandalf.local.home>

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.