netdev - Re: [PATCH] bpf: Allow small structs to be type of function argument

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <CAADnVQLGNUcDWmrgUBmdcgLMfUNf=-3yroA8a+b7s+Ki5Tb4Jg@mail.gmail.com>
Date:   Thu, 18 Jun 2020 19:04:45 -0700
From:   Alexei Starovoitov <alexei.starovoitov@...il.com>
To:     John Fastabend <john.fastabend@...il.com>
Cc:     Andrii Nakryiko <andrii.nakryiko@...il.com>,
        Jiri Olsa <jolsa@...hat.com>, Andrii Nakryiko <andriin@...com>,
        Jiri Olsa <jolsa@...nel.org>,
        Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Networking <netdev@...r.kernel.org>, bpf <bpf@...r.kernel.org>,
        Yonghong Song <yhs@...com>, Martin KaFai Lau <kafai@...com>,
        Jakub Kicinski <kuba@...nel.org>,
        David Miller <davem@...hat.com>,
        Jesper Dangaard Brouer <hawk@...nel.org>,
        KP Singh <kpsingh@...omium.org>,
        Masanori Misono <m.misono760@...il.com>
Subject: Re: [PATCH] bpf: Allow small structs to be type of function argument

On Thu, Jun 18, 2020 at 5:26 PM John Fastabend <john.fastabend@...il.com> wrote:
>
>  foo(int a, __int128 b)
>
> would put a in r0 and b in r2 and r3 leaving a hole in r1. But that
> was some old reference manual and  might no longer be the case
> in reality. Perhaps just spreading hearsay, but the point is we
> should say something about what the BPF backend convention
> is and write it down. We've started to bump into these things
> lately.

calling convention for int128 in bpf is _undefined_.
calling convention for struct by value in bpf is also _undefined_.

In many cases the compiler has to have the backend code
so other parts of the compiler can function.
I didn't bother explicitly disabling every undefined case.
Please don't read too much into llvm generated code.