Re: [Buildroot] NodeJS, qemu wrapper and ELF interpreter fun

From: "Yann E. MORIN" <yann.morin.1998@free.fr>
To: David Laight <David.Laight@ACULAB.COM>
Cc: 'Thomas Petazzoni' <thomas.petazzoni@bootlin.com>,
	"f.rogall@gmx.de" <f.rogall@gmx.de>,
	"mail@jens-maus.de" <mail@jens-maus.de>,
	"buildroot@buildroot.org" <buildroot@buildroot.org>,
	"fesc2000@mailbox.org" <fesc2000@mailbox.org>,
	"oliver.kasten@trsystems.de" <oliver.kasten@trsystems.de>
Subject: Re: [Buildroot] NodeJS, qemu wrapper and ELF interpreter fun
Date: Tue, 1 Nov 2022 11:02:44 +0100	[thread overview]
Message-ID: <20221101100244.GF1058960@scaer> (raw)
In-Reply-To: <f7086aad47234c089332330689ae9a42@AcuMS.aculab.com>

David, All,

On 2022-11-01 08:46 +0000, David Laight spake thusly:
> > (C) Pass LD_LIBRARY_PATH pointing to $(STAGING_DIR)/lib and
> >     $(STAGING_DIR)/usr/lib in the Qemu wrapper. This works because
> >     LD_LIBRARY_PATH paths have precedence over paths given by
> >     ld.so.cache.
> > 
> >     This is the solution already used by the GOI qemu wrapper in
> >     package/gobject-introspection/g-ir-scanner-qemuwrapper.in, and
> >     which was suggested in bug
> >     https://bugs.busybox.net/show_bug.cgi?id=14366.
> > 
> > Any opinion? Or other ideas?
> 
> Using LD_LIBRARY_PATH like that is a bad idea.

Yeah, we know quite a bit about some LD_LIBRARY_PATH woes ;-)

> Just google for it and you'll find a load of stuff about it.
> LD_LIBRARY_PATH should only really be used not substitute a
> non-standard library - eg for testing.

In this situation, the issue is that we are running a *target* program,
on the *build machine*, and we want it to pick target ilbraries, not the
host libraries.

Of course, during cross-compilation, we can't run target code on the
build machine, so we run it through qemu-user.

However, as Thomas explained and demonstrated, qemu-user intercepts and
emulates the open()-like syscalls. Then it has a heuristic to resolve
the opened path. This heuristic fails for us in some cases, however.

Thus we need a way to force-tell where to look for libraries.

So, yes, LD_LIBRARY_PATH is far from a panacea, but technically it makes
things work.

Regards,
Yann E. MORIN.

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