Assertion '!empty()' failed.

[Jark5455]

Hello,

Currently, I am trying to use coz, however whenever I run it with ANY application with no flags I get the following error

/usr/include/c++/14.1.1/bits/basic_string.h:1328: std::__cxx11::basic_string<_CharT, _Traits, _Alloc>::reference std::__cxx11::basic_string<_CharT, _Traits, _Alloc>::front() [with _CharT = char; _Traits = std::char_traits<char>; _Alloc = std::allocator<char>; reference = char&]: Assertion '!empty()' failed.

How do fix?

[Lanzaa]

I think this is related to a bug in the libelfin dependency:

aclements/libelfin#63

[Jark5455]

I applied the patch in the pull request, I am still getting the same error :|

[Lanzaa]

Odd, I am unable to reproduce the issue. Could you include more details?

Also, I would double check that the patch applied and is being used.

[nicholasdejong]

Same issue here. I am not well versed in c++ toolchains, so I had some friction patching the fix.

I am on Arch linux kernel version 6.10.3-arch1-1 which meant downloading from the AUR. I changed cursor.cc, ran make install and copied all the libraries and archives produced by make into the tar from aur. Ran makepkg and installed with pacman. Pretty sure I did something wrong, but I wasn't sure what to actually do.

Still getting the same error message: /usr/include/c++/14.2.1/bits/basic_string.h:1328: std::__cxx11::basic_string<_CharT, _Traits, _Alloc>::reference std::__cxx11::basic_string<_CharT, _Traits, _Alloc>::front() [with _CharT = char; _Traits = std::char_traits<char>; _Alloc = std::allocator<char>; reference = char&]: Assertion '!empty()' failed.

Will do some digging in coz to see if I can fix it.

[WaviestBalloon]

Came here to say that I too am also experiencing this issue:

[libcoz.cpp:100] bootstrapping coz
[libcoz.cpp:128] Including MAIN, which is /home/wav/Documents/httpserver/httpserver-benchmark
/usr/include/c++/14.1.1/bits/basic_string.h:1328: std::__cxx11::basic_string<_CharT, _Traits, _Alloc>::reference std::__cxx11::basic_string<_CharT, _Traits, _Alloc>::front() [with _CharT = char; _Traits = std::char_traits<char>; _Alloc = std::allocator<char>; reference = char&]: Assertion '!empty()' failed.

Currently on Arch Linux, 6.10.7-zen1-1-zen

[Pspritechologist]

Ditto, same error. I'm on Manjaro 24.0.8 and I'm trying to run a Rust binary, although that doesn't seem relevant.

[nicholasdejong]

Ditto, same error. I'm on Manjaro 24.0.8 and I'm trying to run a Rust binary, although that doesn't seem relevant.

Funnily enough, I also tried using coz with Rust, but I doubt that's the problem.

[camelid]

Thanks for the bug reports! Could you provide information about the following?

• which version of coz you're running -- i.e., the commit if from github or the version number and package index you're using.
• an MCVE of how to reproduce the crash -- e.g., a C file, a GCC invocation, and a Coz invocation

This would be super helpful with debugging because I'm not getting an assert failure with either github HEAD (b855f59) or the latest apt package (coz 0.2.2-2).

[Pspritechologist]

Thanks for the bug reports! Could you provide information about the following?

• which version of coz you're running -- i.e., the commit if from github or the version number and package index you're using.
• an MCVE of how to reproduce the crash -- e.g., a C file, a GCC invocation, and a Coz invocation

This would be super helpful with debugging because I'm not getting an assert failure with either github HEAD (b855f59) or the latest apt package (coz 0.2.2-2).

I was using whatever version was on AUR which seems to have not been updated for some time.

I went ahead and cloned from GitHub. Using a version built from that source following the instructions on the repo, I ran coz run --- ./target/debug/<BINARY> after using cargo build to build a Rust file containing only a "Hello, World!" print. I am using a nightly version of the Rust toolchain. That's all the steps I took, I do not have a C file to test with, sorry.

The full output of the program is

[/home/pspritechologist/tempcoz/coz/libcoz/libcoz.cpp:100] bootstrapping coz
[/home/pspritechologist/tempcoz/coz/libcoz/libcoz.cpp:128] Including MAIN, which is /home/pspritechologist/<SRC PATH>/target/debug/<BINARY>
/usr/include/c++/14.1.1/bits/basic_string.h:1328: std::__cxx11::basic_string<_CharT, _Traits, _Alloc>::reference std::__cxx11::basic_string<_CharT, _Traits, _Alloc>::front() [with _CharT = char; _Traits = std::char_traits<char>; _Alloc = std::allocator<char>; reference = char&]: Assertion '!empty()' failed.

[camelid]

Thanks for adding some more info. I'm still unable to reproduce this, which makes me wonder if it could be a problem specific to arch or to newer versions of the kernel. I'm on Ubuntu 22.04.1 (kernel 6.5.0-44-generic). Will do some more digging.

[camelid]

Is this happening for anyone on Ubuntu 22? I can't upgrade right now, so I'm not able to check if it's an Ubuntu vs Arch issue, a kernel version issue, or something else entirely.

[greaka]

I can also reproduce it using the toy.rs example.

Linux 6.10.10-arch1-1 #1 SMP PREEMPT_DYNAMIC Thu, 12 Sep 2024 17:21:02 +0000 x86_64 GNU/Linux
cargo 1.83.0-nightly (80d82ca22 2024-09-27)

Installed via aur coz-git commit 62534a4.

/usr/include/c++/14.1.1/bits/basic_string.h:1328: std::__cxx11::basic_string<_CharT, _Traits, _Alloc>::reference std::__cxx11::basic_string<_CharT, _Traits, _Alloc>::front() [with _CharT = char; _Traits = std::char_traits<char>; _Alloc = std::allocator<char>; reference = char&]: Assertion '!empty()' failed.

[jullanggit]

I have the same issue with the following setup:

Linux 6.11.3-arch1-1 #1 SMP PREEMPT_DYNAMIC Thu, 10 Oct 2024 20:11:06 +0000 x86_64 GNU/Linux
cargo 1.83.0-nightly (15fbd2f60 2024-10-08)
coz from coz-git (aur) commit 62534a4

[camelid]

I just setup an arch vm to try to reproduce this, and I still can't. I ran coz on a simple hello-world C file, a simple hello-world Rust crate, and the toy-rs benchmark. All of them worked fine.

Linux archlinux 6.10.10-arch1-1 #1 SMP PREEMPT_DYNAMIC Thu, 12 Sep 2024 17:21:02 +0000 x86_64 GNU/Linux
g++ (GCC) 14.2.1 20240910
cargo 1.81.0 (2dbb1af80 2024-08-20)

coz installed from source (62534a4)

[camelid]

When installing from git, are you following the instructions here? Obviously they need to be adapted to work on arch linux, but when I did, it worked fine. I also had to export PKG_CONFIG_PATH=/usr/local/lib/pkgconfig:$PKG_CONFIG_PATH and export LD_LIBRARY_PATH=/usr/local/lib:$LD_LIBRARY_PATH for some reason, but that was to fix a cmake config error rather than a coz runtime assert.

[camelid]

Could you go into lldb/gdb and print a backtrace of the assert failure (lldb preferred because usually gives better backtraces)? This is a bit complicated because coz is actually a python script that then loads the coz dylib.

Basically (the (lldb) part is the prompt):

$ lldb ./path/to/benchmark/executable
(lldb) env LD_PRELOAD=/usr/local/lib/libcoz.so
(lldb) env COZ_BINARY_SCOPE=MAIN
(lldb) run
... assert failure printed here ...
(lldb) bt

EDIT: You can also try installing another project from this lab into lldb, which may help with the debugging: https://github.com/plasma-umass/ChatDBG

[Pspritechologist]

Does this seem to be the output you would expect?

[/<HOME_DIR>/coz/libcoz/libcoz.cpp:100] bootstrapping coz
[/<HOME_DIR>/coz/libcoz/libcoz.cpp:128] Including MAIN, which is /<HOME_DIR>/rust_test/target/debug/rust_test
/usr/include/c++/14.1.1/bits/basic_string.h:1328: std::__cxx11::basic_string<_CharT, _Traits, _Alloc>::reference std::__cxx11::basic_string<_CharT, _Traits, _Alloc>::front() [with _CharT = char; _Traits = std::char_traits<char>; _Alloc = std::allocator<char>; reference = char&]: Assertion '!empty()' failed.
Process 39127 stopped
* thread #1, name = 'rust_test', stop reason = signal SIGABRT
    frame #0: 0x00007ffff7d1d3f4 libc.so.6`___lldb_unnamed_symbol3669 + 276
libc.so.6`___lldb_unnamed_symbol3669:
->  0x7ffff7d1d3f4 <+276>: movl   %eax, %ebx
    0x7ffff7d1d3f6 <+278>: negl   %ebx
    0x7ffff7d1d3f8 <+280>: cmpl   $0xfffff000, %eax ; imm = 0xFFFFF000 
    0x7ffff7d1d3fd <+285>: movl   $0x0, %eax

Just let me know if I need to run it differently.

[jullanggit]

I got the following with one of my small projects:

❯ lldb target/coz/poker_bot
(lldb) target create "target/coz/poker_bot"
Current executable set to '/home/julius/.config/rebos/files/common/home/julius/Code/rust/poker_bot/target/coz/poker_bot' (x86_64).
(lldb) env LD_PRELOAD=/usr/local/lib/libcoz.so
(lldb) env COZ_BINARY_SCOPE=MAIN
(lldb)
(lldb) run
Process 159563 launched: '/home/julius/.config/rebos/files/common/home/julius/Code/rust/poker_bot/target/coz/poker_bot' (x86_64)
[/home/julius/coz/libcoz/libcoz.cpp:100] bootstrapping coz
[/home/julius/coz/libcoz/libcoz.cpp:128] Including MAIN, which is /home/julius/.config/rebos/files/common/home/julius/Code/rust/poker_bot/target/coz/poker_bot
/usr/include/c++/14.1.1/bits/basic_string.h:1328: std::__cxx11::basic_string<_CharT, _Traits, _Alloc>::reference std::__cxx11::basic_string<_CharT, _Traits, _Alloc>::front() [with _CharT = char; _Traits = std::char_traits<char>; _Alloc = std::allocator<char>; reference = char&]: Assertion '!empty()' failed.
Process 159563 stopped
* thread #1, name = 'poker_bot', stop reason = signal SIGABRT
    frame #0: 0x00007ffff7d923f4 libc.so.6`___lldb_unnamed_symbol3669 + 276
libc.so.6`___lldb_unnamed_symbol3669:
->  0x7ffff7d923f4 <+276>: movl   %eax, %ebx
    0x7ffff7d923f6 <+278>: negl   %ebx
    0x7ffff7d923f8 <+280>: cmpl   $0xfffff000, %eax ; imm = 0xFFFFF000
    0x7ffff7d923fd <+285>: movl   $0x0, %eax
(lldb) bt
* thread #1, name = 'poker_bot', stop reason = signal SIGABRT
  * frame #0: 0x00007ffff7d923f4 libc.so.6`___lldb_unnamed_symbol3669 + 276
    frame #1: 0x00007ffff7d39120 libc.so.6`raise + 32
    frame #2: 0x00007ffff7d204c3 libc.so.6`abort + 223
    frame #3: 0x00007ffff7ad3af0 libstdc++.so.6`std::__glibcxx_assert_fail(file=<unavailable>, line=<unavailable>, function=<unavailable>, condition=<unavailable>) at assert_fail.cc:41:10
    frame #4: 0x00007ffff7cdaf50 libdwarf++.so.0`dwarf::cursor::string(std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char>>&) + 144
    frame #5: 0x00007ffff7cec714 libdwarf++.so.0`dwarf::line_table::line_table(std::shared_ptr<dwarf::section> const&, unsigned long, unsigned int, std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char>> const&, std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char>> const&) + 2212
    frame #6: 0x00007ffff7ce5944 libdwarf++.so.0`dwarf::compilation_unit::get_line_table() const + 388
    frame #7: 0x00007ffff7f5686a libcoz.so`memory_map::process_file(this=<unavailable>, name=<unavailable>, load_address=<unavailable>, source_scope=<unavailable>) at inspect.cpp:487:48
    frame #8: 0x00007ffff7f59684 libcoz.so`memory_map::build(this=0x0000000000000000, binary_scope=size=0, source_scope=size=0) at inspect.cpp:315:24
    frame #9: 0x00007ffff7f5f333 libcoz.so`wrapped_main(argc=0, argv=0x00007ffff7ffd000, env=0x000055555569a848) at libcoz.cpp:175:13
    frame #10: 0x00007ffff7d21ecc libc.so.6`__libc_start_main + 140
    frame #11: 0x0000555555590025 poker_bot`_start + 37 

[camelid]

Thank you so much! This indicates a bug in the libelfin dependency (that's what libdwarf++ is). Essentially, it calls string::front() on an empty string, which causes an assert failure only when assertions are enabled. They are apparently enabled by default on Arch but not other architectures. I will create a patched version of libelfin soon.

[jullanggit]

Thanks!

[camelid]

Ok, can you try applying this PR's patch to your local libelfin clone? plasma-umass/libelfin#2

Make sure to re-make and make install both libelfin and Coz afterward.

[jullanggit]

Mabe its something on my side, but i get this error when compiling:

cursor.cc: In member function ‘void dwarf::cursor::string(std::string&)’:
cursor.cc:95:27: error: lvalue required as unary ‘&’ operand
   95 |         memmove(&out.c_str(), p, size);
      |                  ~~~~~~~~~^~

[jullanggit]

Chatgpt suggested changing the line to memmove(&out[0], p, size);, which compiles and, as far as I can tell, works!

[camelid]

Whoops, sorry about that. It's actually probably simplest to just guard the original front() call by a condition checking for an empty string. C++ has some weird version-specific behavior around null-termination and thus safety of dereferencing pointers to empty strings.

@jullanggit can you try this updated version of the PR? plasma-umass/libelfin#2

[jullanggit]

I tried it and, as far as I can tell, it works! Thanks!

[camelid]

Awesome! Thanks for your help with the debugging.