netdev - Re: [PATCH bpf-next] bpf: change fake_ip for bpf_trace

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Date:   Thu, 18 Jan 2018 22:13:51 +0100
From:   Daniel Borkmann <daniel@...earbox.net>
To:     Yonghong Song <yhs@...com>, ast@...com, netdev@...r.kernel.org
Cc:     kernel-team@...com
Subject: Re: [PATCH bpf-next] bpf: change fake_ip for bpf_trace_printk helper

On 01/17/2018 06:19 PM, Yonghong Song wrote:
> Currently, for bpf_trace_printk helper, fake ip address 0x1
> is used with comments saying that fake ip will not be printed.
> This is indeed true for 4.12 and earlier version, but for
> 4.13 and later version, the ip address will be printed if
> it cannot be resolved with kallsym. Running samples/bpf/tracex5
> program and you will have the following in the debugfs
> trace_pipe output:
>   ...
>   <...>-1819  [003] ....   443.497877: 0x00000001: mmap
>   <...>-1819  [003] ....   443.498289: 0x00000001: syscall=102 (one of get/set uid/pid/gid)
>   ...
> 
> The kernel commit changed this behavior is:
>   commit feaf1283d11794b9d518fcfd54b6bf8bee1f0b4b
>   Author: Steven Rostedt (VMware) <rostedt@...dmis.org>
>   Date:   Thu Jun 22 17:04:55 2017 -0400
> 
>       tracing: Show address when function names are not found
>   ...
> 
> This patch changed the comment and also altered the fake ip
> address to 0x0 as users may think 0x1 has some special meaning
> while it doesn't. The new output:
>   ...
>   <...>-1799  [002] ....    25.953576: 0: mmap
>   <...>-1799  [002] ....    25.953865: 0: read(fd=0, buf=00000000053936b5, size=512)
>   ...
> 
> Signed-off-by: Yonghong Song <yhs@...com>

Applied to bpf-next, thanks Yonghong!