Stream: beginners

Topic: segfault running hello-world

Nick Gravgaard (Sep 15 2022 at 13:54):

Hi everyone, I've just got around to playing with Roc, but I can't run hello-world or rocLovesRust/rocLovesZig/rocLovesC without getting a segfault. I've tried running different versions of the nightly build as well as installing nix and building roc from source. I'm running Manjaro (an Arch Linux derivative) on an x86-64 laptop.

Any ideas?

Folkert de Vries (Sep 15 2022 at 13:56):

maybe try cargo run -- run --linker=legacy examples/platformSwitching/rocLovesZig.roc

Folkert de Vries (Sep 15 2022 at 13:57):

if nothing else that should give better debug info, my next step would be to see what a debugger says about that segfault

Nick Gravgaard (Sep 15 2022 at 14:08):

Oh that worked, thanks @Folkert de Vries! It seems -- run --linker=legacy is what I needed. Do you know why?

Folkert de Vries (Sep 15 2022 at 14:09):

it uses your system linker, rather than our custom surgical linker. Your OS must do/expect something that our linker does not currently support

Folkert de Vries (Sep 15 2022 at 14:10):

@Brendan Hansknecht what should we do in this case? open an issue for later? collect the elf files that cause issues, or is this a known issue?

Brendan Hansknecht (Sep 15 2022 at 14:16):

Yeah, an issue with elf files would be great as a starting point. Might have to get them to run the surgical linker in verbose mode as well (though I don't think we currently have a way to toggle that without editing source code)

Folkert de Vries (Sep 15 2022 at 14:24):

ok, let's see if we can do this. To get verbose output, find in crates/linker/src/lib.rs

    preprocess(
        target,
        dynhost.to_str().unwrap(),
        metadata.to_str().unwrap(),
        preprocessed_host_path.to_str().unwrap(),
        &dummy_lib,
        false,
        false,
    )
}

pub fn link_preprocessed_host(
    target: &Triple,
    host_input_path: &Path,
    roc_app_obj: &Path,
    binary_path: &Path,
) {
    let metadata = host_input_path.with_file_name("metadata");
    surgery(
        roc_app_obj.to_str().unwrap(),
        metadata.to_str().unwrap(),
        binary_path.to_str().unwrap(),
        false,
        false,
        target,
    )
}

and just change those 4 false bools to true. Then do cargo run -- run examples/platformSwitching/rocLovesZig.roc again, without the linker=legacy this time. It should print a lot of stuff related to linking. Can you put that in a gist and share it here?

Nick Gravgaard (Sep 15 2022 at 14:33):

here we go: https://gist.github.com/nickgravgaard/fddeecf3b34d4d05d93404e3463aa8d6

Folkert de Vries (Sep 15 2022 at 14:40):

thanks, I made https://github.com/roc-lang/roc/issues/4042. Can you maybe add there the files

examples/platform-switching/rocLovesZig
examples/platform-switching/zig-platform/preprocessedhost

Nick Gravgaard (Sep 15 2022 at 14:51):

Done :smile:

Now I have another problem. I can run various command line examples by specifying the linker as you suggested above, but I have a problem with the GUI example. Here's what I get from inside a nix shell:

$ cargo run -- run --linker=legacy examples/gui/Hello.roc
    Finished dev [unoptimized + debuginfo] target(s) in 0.31s
     Running `target/debug/roc run --linker=legacy examples/gui/Hello.roc`
🔨 Rebuilding platform...
/nix/store/vhf2cr6immz4qdxd83y025fnxim8mmfg-binutils-2.38/bin/ld: examples/gui/platform/host.o:(.data._rust_extern_with_linkage___dso_handle+0x0): undefined reference to `__dso_handle'
/nix/store/vhf2cr6immz4qdxd83y025fnxim8mmfg-binutils-2.38/bin/ld: /nix/store/6f66prpgx1qx4n6k450sxs3d157ia1ps-glibc-2.35-163/lib/libc_nonshared.a(pthread_atfork.oS): in function `__pthread_atfork':
(.text+0x7): undefined reference to `__dso_handle'
/nix/store/vhf2cr6immz4qdxd83y025fnxim8mmfg-binutils-2.38/bin/ld: examples/gui/hello-gui: hidden symbol `__dso_handle' isn't defined
/nix/store/vhf2cr6immz4qdxd83y025fnxim8mmfg-binutils-2.38/bin/ld: final link failed: bad value
1 error and 0 warnings found in 37699 ms.

Running program anyway…

────────────────────────────────────────────────────────────────────────────────
thread 'main' panicked at 'called `Result::unwrap()` on an `Err` value: Os { code: 2, kind: NotFound, message: "No such file or directory" }', crates/cli/src/lib.rs:639:61
note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace```

Folkert de Vries (Sep 15 2022 at 16:00):

thanks. Clearly something is not right with the linker on your system. @Anton does this look familiar at all?

Richard Feldman (Sep 15 2022 at 16:05):

I wonder if it might be easier to fix the surgical linking bug than to debug what's wrong with ld :thinking:

Richard Feldman (Sep 15 2022 at 16:05):

maybe with a pair programming session?

Nick Gravgaard (Sep 15 2022 at 16:25):

I've got to go now, but I'll be around tomorrow from 9am to 4pm UK time if you need me

Anton (Sep 16 2022 at 06:14):

The undefined reference to __dso_handle is a known issue when we use a GUI and the legacy linker, we always ended up using the surgical linker instead. I will write up an issue.

Nick Gravgaard (Sep 16 2022 at 13:58):

Here's the new issue: https://github.com/roc-lang/roc/issues/4049

Can anyone give me some pointers about how I might try to fix it? I'm happy to pair as @Richard Feldman suggested.

Brendan Hansknecht (Sep 16 2022 at 14:46):

I'm going to take a look today, but pointers around fixing may be hard. Just a lot of potential problems. Likely starting with objdump and gdb to see what they say.

Anton (Sep 16 2022 at 15:14):

Yeah #4049 may be difficult and since the surgical linker is the default it may be best to attempt to fix #4042 first.

Anton (Sep 16 2022 at 15:16):

For #4042 it would be helpful to add the output of valgrind --leak-check=full --track-origins=yes ./examples/hello-world/helloWorld to the issue.

Brendan Hansknecht (Sep 16 2022 at 15:47):

Oh, i just realized this is a different issue than #4042....oops. I guess I mixed up the threads.

Nick Gravgaard (Sep 16 2022 at 15:58):

This is strange. It looks like the helloWorld binary works when run through valgrind but not when run directly:

[nick@nick-x270 roc]$ cargo run examples/hello-world/main.roc
<lots of debug info snipped>
Segmentation fault
[nick@nick-x270 roc]$ ./examples/hello-world/helloWorld
Segmentation fault
[nick@nick-x270 roc]$ valgrind --leak-check=full --track-origins=yes ./examples/hello-world/helloWorld
==60130== Memcheck, a memory error detector
==60130== Copyright (C) 2002-2022, and GNU GPL'd, by Julian Seward et al.
==60130== Using Valgrind-3.19.0 and LibVEX; rerun with -h for copyright info
==60130== Command: ./examples/hello-world/helloWorld
==60130==
Hello, World!
==60130==
==60130== HEAP SUMMARY:
==60130==     in use at exit: 0 bytes in 0 blocks
==60130==   total heap usage: 0 allocs, 0 frees, 0 bytes allocated
==60130==
==60130== All heap blocks were freed -- no leaks are possible
==60130==
==60130== For lists of detected and suppressed errors, rerun with: -s
==60130== ERROR SUMMARY: 0 errors from 0 contexts (suppressed: 0 from 0)

Am I doing something wrong?

Anton (Sep 16 2022 at 16:01):

The executable by itself will also work, we've seen this stuff before, I'll write up an issue.

Nick Gravgaard (Sep 16 2022 at 16:04):

@Anton what do you mean by "The executable by itself will also work". Isn't that what I'm doing when I run "./examples/hello-world/helloWorld"? (which segfaults when I do it on line 4 of the console output above)

Anton (Sep 16 2022 at 16:04):

Oops, yes this is different

Anton (Sep 16 2022 at 16:05):

Yeah, this makes no sense :p

Brendan Hansknecht (Sep 16 2022 at 16:20):

Yeah, i was just doing some testing and realized the same. Executable is valid

Brendan Hansknecht (Sep 16 2022 at 16:21):

What happens if you run directly? What is the actual output?

Nick Gravgaard (Sep 16 2022 at 21:29):

[nick@nick-x270 roc]$ ./examples/hello-world/helloWorld
Segmentation fault

If I run it using cargo run -- run examples/hello-world/main.rocI get this output: https://gist.github.com/nickgravgaard/56f1bb23ff088df8aaada11930cbf90a

Folkert de Vries (Sep 16 2022 at 21:31):

so the "running" part produces no output whatsoever?

Folkert de Vries (Sep 16 2022 at 21:32):

that gist mostly shows the verbose surgical linker output

Nick Gravgaard (Sep 16 2022 at 21:32):

That's right, I don't see anything except the Segmentation fault text

Brendan Hansknecht (Sep 16 2022 at 21:47):

Can you run it with gdb or lldb?

Brendan Hansknecht (Sep 16 2022 at 21:50):

Also, could you share the output of ldd <segfaulting executable>

Nick Gravgaard (Sep 16 2022 at 21:54):

Here's the output from ldd:

[nick@nick-x270 roc]$ ldd ./examples/hello-world/helloWorld
    linux-vdso.so.1 (0x00007f44fd90f000)
    libm.so.6 => /nix/store/6f66prpgx1qx4n6k450sxs3d157ia1ps-glibc-2.35-163/lib/libm.so.6 (0x00007f44fd7ec000)
    libpthread.so.0 => /nix/store/6f66prpgx1qx4n6k450sxs3d157ia1ps-glibc-2.35-163/lib/libpthread.so.0 (0x00007f44fd7e7000)
    libdl.so.2 => /nix/store/6f66prpgx1qx4n6k450sxs3d157ia1ps-glibc-2.35-163/lib/libdl.so.2 (0x00007f44fd7e0000)
    librt.so.1 => /nix/store/6f66prpgx1qx4n6k450sxs3d157ia1ps-glibc-2.35-163/lib/librt.so.1 (0x00007f44fd7db000)
    libutil.so.1 => /nix/store/6f66prpgx1qx4n6k450sxs3d157ia1ps-glibc-2.35-163/lib/libutil.so.1 (0x00007f44fd7d6000)
    libc.so.6 => /nix/store/6f66prpgx1qx4n6k450sxs3d157ia1ps-glibc-2.35-163/lib/libc.so.6 (0x00007f44fd5cc000)
    /nix/store/6f66prpgx1qx4n6k450sxs3d157ia1ps-glibc-2.35-163/lib/ld-linux-x86-64.so.2 => /nix/store/6f66prpgx1qx4n6k450sxs3d157ia1ps-glibc-2.35-163/lib64/ld-linux-x86-64.so.2 (0x00007f44fd911000)

Nick Gravgaard (Sep 16 2022 at 21:56):

gdbcomplains, and I don't have lldb installed in this nix shell:

[nick@nick-x270 roc]$ gdb
gdb: /nix/store/cs16l9whsq2mgydlg0j4x517z4qr861k-gcc-11.3.0-lib/lib/libstdc++.so.6: version `GLIBCXX_3.4.30' not found (required by gdb)
gdb: /nix/store/cs16l9whsq2mgydlg0j4x517z4qr861k-gcc-11.3.0-lib/lib/libstdc++.so.6: version `GLIBCXX_3.4.30' not found (required by /usr/lib/libsource-highlight.so.4)
gdb: /nix/store/cs16l9whsq2mgydlg0j4x517z4qr861k-gcc-11.3.0-lib/lib/libstdc++.so.6: version `GLIBCXX_3.4.30' not found (required by /usr/lib/libboost_regex.so.1.79.0)

[nick@nick-x270 roc]$ lldb
bash: lldb: command not found

Nick Gravgaard (Sep 16 2022 at 21:57):

I'm available to pair now if it helps

Nick Gravgaard (Sep 16 2022 at 21:59):

I'm installing lldb now

Brendan Hansknecht (Sep 16 2022 at 22:04):

I am going to guess that it is a versioning issue between nix versions of those libraries and your system versions of the libraries. Not sure a fix at the moment, but that is my base guess.

Brendan Hansknecht (Sep 16 2022 at 22:04):

Also, sadly can't pair now.

Brendan Hansknecht (Sep 16 2022 at 22:06):

As in, the platform is pulling in system libraries when it builds, but when the app runs the dynamic library resolution pulls in the nix versions. Some libc call or setup or something has versioning issues that lead to the segfault.

Brendan Hansknecht (Sep 16 2022 at 22:07):

One test would be: completely out of anything nix, run the precompiled nightly build of roc on a cleaned hello world.

Nick Gravgaard (Sep 16 2022 at 22:21):

No, that doesn't work. I had segfaults running hello-world using the precompiled nightly build before I installed nix.

Brendan Hansknecht (Sep 16 2022 at 22:24):

Interesting. Can you run ldd outside of nix on that? It shouldn't point to nix store stuff.

Nick Gravgaard (Sep 16 2022 at 22:32):

$ ldd examples/hello-world/helloWorld
    linux-vdso.so.1 => linux-vdso.so.1 (0x00007ffccad5c000)
    libm.so.6 => /usr/lib/libm.so.6 (0x00007f11fbae3000)
    libc.so.6 => /usr/lib/libc.so.6 (0x00007f11fb8fc000)
    /lib64/ld-linux-x86-64.so.2 => /usr/lib64/ld-linux-x86-64.so.2 (0x00007f11fbc37000)

Nick Gravgaard (Sep 16 2022 at 22:34):

Here's lldb too

$ lldb examples/hello-world/helloWorld
/home/nick/.nix-profile/bin/lldb: error while loading shared libraries: liblzma.so.5: cannot open shared object file: No such file or directory

Brendan Hansknecht (Sep 16 2022 at 23:01):

Wait...error loading a shared library that the executable didn't even request?

Brendan Hansknecht (Sep 16 2022 at 23:01):

I guess you can try seeing what it takes to install liblzma on arch?

Last updated: Jul 26 2025 at 12:14 UTC