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

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Date:   Fri, 15 Mar 2019 15:05:54 -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:
> 
> ----- Stanislav Fomichev <sdf@...ichev.me> wrote:
> > 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.
> 
> Without that additional call this does not work and build_id selftest fails.
Oh, yeah, I was just trying to clarify why it fails without -static and why
your patch makes it work for non-static :-)
You can put more details in the commit message; you'd have to resubmit
whenever net-next/bpf-next opens anyway.

> 
> I.