netdev - Re: [PATCH v6 bpf-next 08/11] bpf: introduce BPF_RAW

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Message-ID: <b0763759-3f8b-317b-5fb4-600648495462@fb.com>
Date:   Tue, 27 Mar 2018 17:00:23 -0700
From:   Alexei Starovoitov <ast@...com>
To:     Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
CC:     rostedt <rostedt@...dmis.org>,
        "David S. Miller" <davem@...emloft.net>,
        Daniel Borkmann <daniel@...earbox.net>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Peter Zijlstra <peterz@...radead.org>,
        netdev <netdev@...r.kernel.org>,
        kernel-team <kernel-team@...com>,
        linux-api <linux-api@...r.kernel.org>,
        Kees Cook <keescook@...omium.org>
Subject: Re: [PATCH v6 bpf-next 08/11] bpf: introduce BPF_RAW_TRACEPOINT

On 3/27/18 4:13 PM, Mathieu Desnoyers wrote:
> ----- On Mar 27, 2018, at 6:48 PM, Alexei Starovoitov ast@...com wrote:
>
>> On 3/27/18 2:04 PM, Steven Rostedt wrote:
>>>
>>> +#ifdef CONFIG_BPF_EVENTS
>>> +#define BPF_RAW_TP() . = ALIGN(8);		\
>
> Given that the section consists of a 16-bytes structure elements
> on architectures with 8 bytes pointers, this ". = ALIGN(8)" should
> be turned into a STRUCT_ALIGN(), especially given that the compiler
> is free to up-align the structure on 32 bytes.

STRUCT_ALIGN fixed the 'off by 8' issue with kasan,
but it fails without kasan too.
For some reason the whole region __start__bpf_raw_tp - __stop__bpf_raw_tp
comes inited with cccc:
[   22.703562] i 1 btp ffffffff8288e530 btp->tp cccccccccccccccc func 
cccccccccccccccc
[   22.704638] i 2 btp ffffffff8288e540 btp->tp cccccccccccccccc func 
cccccccccccccccc
[   22.705599] i 3 btp ffffffff8288e550 btp->tp cccccccccccccccc func 
cccccccccccccccc
[   22.706551] i 4 btp ffffffff8288e560 btp->tp cccccccccccccccc func 
cccccccccccccccc
[   22.707503] i 5 btp ffffffff8288e570 btp->tp cccccccccccccccc func 
cccccccccccccccc
[   22.708452] i 6 btp ffffffff8288e580 btp->tp cccccccccccccccc func 
cccccccccccccccc
[   22.709406] i 7 btp ffffffff8288e590 btp->tp cccccccccccccccc func 
cccccccccccccccc
[   22.710368] i 8 btp ffffffff8288e5a0 btp->tp cccccccccccccccc func 
cccccccccccccccc

while gdb shows that everything is good inside vmlinux
for exactly these addresses.
Some other linker magic missing?