linux-kernel - Re: [PATCH net-next] selftests: bpf: modify urandom

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Message-ID: <20190315205652.GD5481@mini-arch.hsd1.ca.comcast.net>
Date:   Fri, 15 Mar 2019 13:56:52 -0700
From:   Stanislav Fomichev <sdf@...ichev.me>
To:     Ivan Vecera <ivecera@...hat.com>
Cc:     netdev@...r.kernel.org, Shuah Khan <shuah@...nel.org>,
        Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Martin KaFai Lau <kafai@...com>,
        Song Liu <songliubraving@...com>, Yonghong Song <yhs@...com>,
        "open list:KERNEL SELFTEST FRAMEWORK" 
        <linux-kselftest@...r.kernel.org>,
        "open list:BPF (Safe dynamic programs and tools)" 
        <bpf@...r.kernel.org>, open list <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH net-next] selftests: bpf: modify urandom_read and link it
 non-statically

On 03/15, Ivan Vecera wrote:
> On 15. 03. 19 21:08, Stanislav Fomichev wrote:
> > On 03/15, Ivan Vecera wrote:
> > > After some experiences I found that urandom_read does not need to be
> > > linked statically. When the 'read' syscall call is moved to separate
> > > non-inlined function then bpf_get_stackid() is able to find
> > > the executable in stack trace and extract its build_id from it.
> > But why? Do you have some problems with it being linked statically?
> > 
> Dependency... you don't need to install static glibc to compile the bpf
> samples. Shared libc is available everytime.
Oh, the distros that do -devel _and_ -static packages :-)

So your patch essentially adds a call, that leaves a trace on the stack
with our build-id. I guess that works as well.

> 
> Ivan