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Date: Sun, 5 Nov 2023 09:01:59 -0800
From: Fangrui Song <i@...kray.me>
To: musl@...ts.openwall.com
Cc: Farid Zakaria <fmzakari@...c.edu>
Subject: Re: dynlink.c tests
> Is there a dynamic-loader test suite anyone is familiar with ?
FreeBSD rtld-elf has very few test
https://github.com/freebsd/freebsd-src/tree/main/libexec/rtld-elf/tests
glibc/elf contains extensive rtld tests. The Makefile-based test
system may be a bit tricky to deal with... but the coverage is quite
decent.
`configure --enable-hardcoded-path-in-tests` makes it easy to invoke a test.
On Mon, Oct 23, 2023 at 5:04 PM Rich Felker <dalias@...c.org> wrote:
>
> On Mon, Oct 23, 2023 at 11:08:31AM -0700, Farid Zakaria wrote:
> > Just to be pedantic, few ideas come to mind:
> > - One could change the symbol count method to only use DT_HASH and it
> > would succeed until GCC removed it ;)
>
> There are already distros building with GNU-hash-only, so one of them
> would catch such breakage.
Yes.
(For the curious, https://maskray.me/blog/2023-04-12-elf-hash-function
describes a bug in *BSD that dlsym(dl, "ZZZZZW9p") returned NULL for a
DSO linked with -shared -fuse-ld=lld -Wl,--hash-style=sysv.)
> > - The order of resolution for dependencies
>
> This has changed before from whatever-it-was to something very
> intentional, and basic testing of the intended order was done at the
> time, but we don't have regularly run tests for it. While future
> changes here would come with manual testing like that again, it would
> be nice to have an automated framework for this.
Absolutely! Things like the path precedence, constructor order, etc
will be very useful to have test coverage.
> > - $ORIGIN replacement
>
> This is probably under-tested but I'm not aware of any reported bugs,
> and it's not code that's churning.
>
> > I am very appreciative of the codebase.
> > I'm going through it at the moment "stripping it down" a bit to be for
> > x86-64 and adding some comments to help me better understand the
> > process.
>
> I'm not sure that makes much sense. The code as it is isn't overly
> general or using any expensive abstraction layers to support all
> archs. It's very intentionally designed around the concept that all
> archs are basically the same in regards to how dynamic linking works.
> Trying to specialize to just supporting one *obscures* that property
> and makes the arch-specific naming/numbering of relocation types, etc.
> look like a relevant difference when it's not.
>
> > I was going to look at whether I can take on a C++ standard as a
> > dependency as well.
>
> I mean you can do whatever you like in your own hacking around, but
> without being really intentional about what parts of C++ you do and
> don't use, it's easy to pull in circular dependencies, dependencies on
> things that depend on stuff before it has been (and before it's
> possible to have been) initialized, etc.
>
> Also, of course, C and C++ are different languages -- in particular,
> C++ is a not a superset of C. There's no guarantee that any of the
> code in musl behaves as intended when compiled as C++, because it's
> not C++. This wouldn't matter if you're working with separate C++ TUs
> but it would possibly matter if you started trying to put C++ in
> existing C files.
>
> Rich
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