Re: [PING PATCH v7] kallsyms: new /proc/kallmodsyms with builtin modules

From: Daniel Xu <dxu@dxuuu.xyz>
To: Luis Chamberlain <mcgrof@kernel.org>
Cc: "Nick Alcock" <nick.alcock@oracle.com>,
	"bas smit" <bas@baslab.org>, "Tomáš Glozar" <tglozar@gmail.com>,
	Ast-x64 <Ast-x64@protonmail.com>,
	"Viktor Malik" <viktor.malik@gmail.com>,
	"Jiri Olsa" <jolsa@kernel.org>,
	jeyu@kernel.org, masahiroy@kernel.org,
	linux-modules@vger.kernel.org, linux-kernel@vger.kernel.org,
	arnd@arndb.de, akpm@linux-foundation.org, eugene.loh@oracle.com,
	kris.van.hees@oracle.com
Subject: Re: [PING PATCH v7] kallsyms: new /proc/kallmodsyms with builtin modules
Date: Wed, 2 Feb 2022 10:10:47 -0800	[thread overview]
Message-ID: <20220202181047.frwirxdpufwzkbv3@kashmir.localdomain> (raw)
In-Reply-To: <Yfn145FyE3PDBEad@bombadil.infradead.org>

Hi Luis, Nick,

On Tue, Feb 01, 2022 at 07:09:23PM -0800, Luis Chamberlain wrote:
[...]
> 
> I don't see much traction based on what you have said on dtrace
> on anything other than Oracle Linux stuff, it would be nice if bpftrace
> folks were excited about your changes and we had support for that
> there.

I took a quick look at the v7 cover letter (I'll take a look at
discussion from previous versions later if I get time) and it's not
immediately obvious to me why a stable mapping is beneficial.

Nick, could you elaborate why it's beneficial for dtrace to have a
stable mapping?

For what it's worth, bpftrace uses /proc/kallsyms rather rarely.
bpftrace relies on perf_event_open()'s config1 parameter to resolve
kernel symbol name to address for kprobe attachment. /proc/kallsyms is
mostly used to resolve kaddr() calls in bpftrace scripts.

Kernel symbol size information would be useful, though. bpftrace
currently uses the vmlinux ELF to acquire that information.

[...]

Thanks,
Daniel