Tools for dumping information about .rlibs

[novocaine]

It would be great if there was a set of tools for dumping information about a given .rlib. This could be used to debug linkage and export issues.

Something like nm and ldd.

I note that nm does appear to partly work on a .rlib, but the output is a bit raw.

Where is the best place to start for understanding the .rlib format as it stands? Is it a good idea to build this on rustc::metadata?

See also http://stackoverflow.com/questions/24603672/rust-library-for-inspecting-rlib-binaries

[lifthrasiir]

cc me

For inspecting metadata this tool might be a good starting point. I have a version of that for post-reform metadata, I'll update the script soon.

[novocaine]

👍

[alexcrichton]

All rlibs are actually just static archives (e.g. *.a files) so tools like nm and ar will work on them naturally assuming they ignore the non-object files located within (e.g. metadata and bytecode). As @lifthrasiir mentioned, however, I'd love to have a tool to inspect the metadata in more detail to, for example, dump a module structure, type signatures, etc. The metadata format is a huge black box and is indeed all centralized around rustc::metadata. Note that a tool which does lots and lots with metadata will likely want to be tightly integrated to rustdoc as well as rustdoc already has tons of code to inspect metadata and reconstruct ASTs and/or module hierarchies.

[novocaine]

Would you expect ldd to work?

Otool on os x does not

[alexcrichton]

I think that ldd and otool only work on actual elf files like dynamic libraries and executables, so in that sense no I wouldn't expect them to work.

[novocaine]

(sorry about the 20 questions, but I can't find any resources on this stuff)

How do .rlibs link against 'normal' dynamic libraries provided to rustc via -l ? Is there an ELF image inside the ar somewhere that's dynamically linked against them? Or does rust embed dynamic loader code e.g dlopen?

[alexcrichton]

but I can't find any resources on this stuff

That... may be because none exist :(. I'm more than willing to answer questions though!

How do .rlibs link against 'normal' dynamic libraries provided to rustc via -l ?

No actual linkage occurs, the compiler emits information into the rlib metadata saying what dynamic native libraries should be linked in later, but they're not actually linked until the rlib is linked into a dylib or executable. If the rlib is later used to assemble a staticlib the compiler just prints out what native libraries are needed to link everything.

Is there an ELF image inside the ar somewhere that's dynamically linked against them?

Nah the only ELF file inside rlibs is the object file that the compiler generates (and possibly the object files of native static libraries linked against).

Or does rust embed dynamic loader code e.g dlopen?

No the compiler doesn't embed any code like this in this respect.

[novocaine]

Thanks, Alex :)