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Message-ID: <20210717184010.246e7895@vostro>
Date: Sat, 17 Jul 2021 18:40:10 +0300
From: Timo Teras <timo.teras@....fi>
To: Rich Felker <dalias@...c.org>
Cc: musl@...ts.openwall.com
Subject: Re: option to enable eh_frame
On Sat, 17 Jul 2021 09:25:44 -0400
Rich Felker <dalias@...c.org> wrote:
> > Please add in any reasons I may have missed. I would like to have
> > your complete list of reasons why to remove .eh_frame. So far it
> > has been coming out in pieces. I'd like constructive discussion if
> > some of these items could be implemented stronger in other means
> > than removing ..eh_frame.
>
> You're coming at it from the wrong direction. For new, nonstandard
> functionality requests, musl has a well established process of
> criteria for inclusion and exclusion, based on invasiveness (this is
> not just a matter of code change size, but of constraints it imposes),
> size, how often the lack of the functionality impacts portable or
> important FOSS programs users want to run on musl, and whether there
> are other ways the applications that want it could achieve what they
> want. In this case, all of those criteria indicate against doing it.
Just to be on record, musl used to include .eh_frame until 2012 and
commit b439c051c7eee4eb4b93fc382f993aa6305ce530 or musl 0.9.5. So back
then existing "contract" was broken. If this discussion was done then,
this would be the other angle: why to break something that is working.
> > But fundamentally I think if we ship .debug_frame, all people
> > wanting do backtrace() and the silly stuff, will just enable
> > .debug_frame support in their code and still do the silly stuff in
> > worse way, than if .eh_frame was enabled. Since technically they
> > are the same, even if the intended use case is different. As seen
> > libunwind does have --enable-debug-frame.
>
> They might, but then they're clearly using a debugging interface that
> only works when debug files are available (or if you include this in
> main libc.so, when libc.so is not stripped).
But how is this different from the "contract" viewpoint?
You are agreeable to have .debug_frame by default in the main DSO. And
if we make musl have .debug_frame, and build libunwind with
--enable-debug-frame, the user gets quite similar "contract" experience
as with .eh_frame. But just worse than having .eh_frame, because for the
unwinder to be able to use .debug_frame it needs to do more silly
things.
Users don't care if it's .debug_frame or .eh_frame as long as the higher
level functionality works. And it gives same "de facto contract"
experience.
Sorry for being "stupid" here, but I'm trying to understand your
viewpoint. So far it's sounding like:
- same things can be achieved by doing X or Y
- you argue X is evil and breaking contract, but Y is ok
- on system/user level the "contract" or "experience" is same
regardless of doing X or Y
Basically I'm trying to understand why do you consider .eh_frame so
much more important "contract" than .debug_frame?
Timo
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