-Zbuild-std + lto="fat" = undefined reference to `core::panicking::panic`

[tmiasko]

$ cargo new --bin a
     Created binary (application) `a` package
$ cd a/
$ echo -e '[profile.dev]\nlto="fat"' >> Cargo.toml 
$ cargo run -Zbuild-std --target x86_64-unknown-linux-gnu
...
error: linking with `cc` failed: exit code: 1
  |
  = note: "cc" "-Wl,--as-needed" "-Wl,-z,noexecstack" "-m64" "-L" "/../.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/x86_64-unknown-linux-gnu/lib" "/tmp/a/target/x86_64-unknown-linux-gnu/debug/deps/a-f6afee8bd619dd6c.10btgdcccpdgwv38.rcgu.o" "-o" "/tmp/a/target/x86_64-unknown-linux-gnu/debug/deps/a-f6afee8bd619dd6c" "-Wl,--gc-sections" "-pie" "-Wl,-zrelro" "-Wl,-znow" "-nodefaultlibs" "-L" "/tmp/a/target/x86_64-unknown-linux-gnu/debug/deps" "-L" "/tmp/a/target/debug/deps" "-L" "/tmp/a/target/x86_64-unknown-linux-gnu/debug/build/backtrace-sys-23683e5572d20c8c/out" "-L" "/../.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/x86_64-unknown-linux-gnu/lib" "-Wl,--start-group" "-Wl,-Bstatic" "/tmp/rustcgyDZiW/libbacktrace_sys-ba159dd14189807b.rlib" "-Wl,--end-group" "/tmp/a/target/x86_64-unknown-linux-gnu/debug/deps/libcompiler_builtins-495badfa0e51e0a1.rlib" "-Wl,-Bdynamic" "-ldl" "-lrt" "-lpthread" "-lgcc_s" "-lc" "-lm" "-lrt" "-lpthread" "-lutil" "-lutil"
  = note: /usr/bin/ld: /tmp/a/target/x86_64-unknown-linux-gnu/debug/deps/libcompiler_builtins-495badfa0e51e0a1.rlib(compiler_builtins-495badfa0e51e0a1.compiler_builtins.ecun6ipv-cgu.15.rcgu.o): in function `<i128 as core::ops::arith::Sub>::sub':
          /../.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/src/rust/src/libcore/ops/arith.rs:194: undefined reference to `core::panicking::panic'
          /usr/bin/ld: /tmp/a/target/x86_64-unknown-linux-gnu/debug/deps/libcompiler_builtins-495badfa0e51e0a1.rlib(compiler_builtins-495badfa0e51e0a1.compiler_builtins.ecun6ipv-cgu.11.rcgu.o): in function `compiler_builtins::int::sdiv::Div::div':
          /../.cargo/registry/src/github.com-1ecc6299db9ec823/compiler_builtins-0.1.25/src/int/sdiv.rs:6: undefined reference to `core::panicking::panic'
          /usr/bin/ld: /../.cargo/registry/src/github.com-1ecc6299db9ec823/compiler_builtins-0.1.25/src/int/sdiv.rs:7: undefined reference to `core::panicking::panic'
          /usr/bin/ld: /tmp/a/target/x86_64-unknown-linux-gnu/debug/deps/libcompiler_builtins-495badfa0e51e0a1.rlib(compiler_builtins-495badfa0e51e0a1.compiler_builtins.ecun6ipv-cgu.11.rcgu.o): in function `compiler_builtins::int::sdiv::Mod::mod_':
          /../.cargo/registry/src/github.com-1ecc6299db9ec823/compiler_builtins-0.1.25/src/int/sdiv.rs:28: undefined reference to `core::panicking::panic'
          /usr/bin/ld: /../.cargo/registry/src/github.com-1ecc6299db9ec823/compiler_builtins-0.1.25/src/int/sdiv.rs:31: undefined reference to `core::panicking::panic'
          /usr/bin/ld: /tmp/a/target/x86_64-unknown-linux-gnu/debug/deps/libcompiler_builtins-495badfa0e51e0a1.rlib(compiler_builtins-495badfa0e51e0a1.compiler_builtins.ecun6ipv-cgu.13.rcgu.o):/../.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/src/rust/src/libcore/ops/bit.rs:515: more undefined references to `core::panicking::panic' follow
          collect2: error: ld returned 1 exit status
          

error: aborting due to previous error

Looks like this is either an issue with compiler-builtins which should avoid
using any checked operations which could generate references to core crate, or
an issue with cargo -Zbuild-std which should always built this crate with
-Coverflow-checks=no.

[josephlr]

We encountered a similar issue in cloud-hypervisor/rust-hypervisor-firmware#69 where the following three features in combination resulted in a link failure:

• LTO
• debug build
• -Zbuild-std

However, our issues weren't solved by just using overflow-checks = false or by disabling debug assertions. We had to disable LTO or set opt-level = 1.

The issue seems to be that when libcore/compiler-builtins is built with LTO, compiler-builtins still needs to reference some functions from libcore (like core::ptr::const_ptr::offset or core::panicking::panic). However, these functions get eliminated from the main binary due to LTO, so compiler-builtins ends up with undefined references. This doesn't happen with opt-level = 1 as the calls from compiler-builtins to libcore are inlined, removing any LTO related issues.

[alexcrichton]

This crate is designed to in theory not reference any symbols from libcore. If that happens there's a bug in this crate. For example no functions should panic, and nothing should be referencing functions upstream in libcore itself.

[Rahix]

I'm also facing this on AVR:

   Compiling arduino-leonardo v0.1.0 (/avr-hal/boards/arduino-leonardo)
error: linking with `avr-gcc` failed: exit code: 1
  |
  = note: "avr-gcc" "-mmcu=atmega32u4" "-Wl,--as-needed" "-L" "/rust/build/x86_64-unknown-linux-gnu/stage1/lib/rustlib/avr-atmega32u4/lib" "/avr-hal/target/avr-atmega32u4/debug/examples/rahix_are_we_large_int_yet-2408b37d61755303.panic_halt-adf0e0db19dc9c4b.panic_halt.524x37ge-cgu.0.rcgu.o.rcgu.o" "-o" "/avr-hal/target/avr-atmega32u4/debug/examples/rahix_are_we_large_int_yet-2408b37d61755303.elf" "-Wl,--gc-sections" "-no-pie" "-L" "/avr-hal/target/avr-atmega32u4/debug/deps" "-L" "/avr-hal/target/debug/deps" "-L" "/rust/build/x86_64-unknown-linux-gnu/stage1/lib/rustlib/avr-atmega32u4/lib" "-Wl,--start-group" "-Wl,--end-group" "-Wl,-Bstatic" "/avr-hal/target/avr-atmega32u4/debug/deps/libcompiler_builtins-03d212bc2672989c.rlib" "-Wl,-Bdynamic" "-lgcc"
  = note: /usr/bin/avr-ld: /avr-hal/target/avr-atmega32u4/debug/deps/libcompiler_builtins-03d212bc2672989c.rlib(compiler_builtins-03d212bc2672989c.compiler_builtins.elxguzph-cgu.7.rcgu.o): in function `compiler_builtins::int::shift::Ashl::ashl':
          /home/rahix/.cargo/registry/src/github.com-1ecc6299db9ec823/compiler_builtins-0.1.36/src/int/shift.rs:(.text._ZN17compiler_builtins3int5shift4Ashl4ashl17hfb01a5f265cfc56eE+0x150): undefined reference to `core::panicking::panic'
          /usr/bin/avr-ld: /avr-hal/target/avr-atmega32u4/debug/deps/libcompiler_builtins-03d212bc2672989c.rlib(compiler_builtins-03d212bc2672989c.compiler_builtins.elxguzph-cgu.7.rcgu.o): in function `compiler_builtins::int::shift::Lshr::lshr':
          /home/rahix/.cargo/registry/src/github.com-1ecc6299db9ec823/compiler_builtins-0.1.36/src/int/shift.rs:(.text._ZN17compiler_builtins3int5shift4Lshr4lshr17hdf6ef8cc4c3c992bE+0x1f8): undefined reference to `core::panicking::panic'
          /usr/bin/avr-ld: /avr-hal/target/avr-atmega32u4/debug/deps/libcompiler_builtins-03d212bc2672989c.rlib(compiler_builtins-03d212bc2672989c.compiler_builtins.elxguzph-cgu.1.rcgu.o): in function `compiler_builtins::int::specialized_div_rem::u32_div_rem':
          /home/rahix/.cargo/registry/src/github.com-1ecc6299db9ec823/compiler_builtins-0.1.36/src/int/specialized_div_rem/delegate.rs:95: undefined reference to `core::panicking::panic'
          collect2: error: ld returned 1 exit status

However, for me, adding overflow-checks = false does fix it:

[profile.dev.package.compiler_builtins]
overflow-checks = false

Curiously, I get a warning about this not being used, but it works:

warning: profile package spec `compiler_builtins` in profile `dev` did not match any packages
   Compiling compiler_builtins v0.1.36
   Compiling bare-metal v0.2.5
   Compiling nb v1.0.0
   Compiling vcell v0.1.2
[...]
   Compiling arduino-leonardo v0.1.0 (/avr-hal/boards/arduino-leonardo)
    Finished dev [optimized + debuginfo] target(s) in 11.24s

As @tmiasko wrote, maybe compiler-builtins should actually specify overflow-checks = false by itself?

[alecmocatta]

I'm also seeing this with WASM: there's an undefined reference to _ZN4core9panicking5panic17he4861068bc6d1d99E in __multi3 which causes wasm-bindgen to fail with cannot import from modules ('env') with '--no-modules'.

I see the same behaviour as @Rahix: the profile package spec triggers a warning but does actually work.

[jonahbron]

I encountered this issue as well, and fixed it with the setting mentioned by @Rahix . This issue cropped up in my program when I introduced a usage of core::cell::RefCell, not sure if that's related. I found this comment by googling "avr undefined reference to core panicking panic"

[lexxvir]

I'd like to note that the issue still occurs (one year already) and existing workaround is slightly annoying when building crates.

[Amanieu]

This should be fixed in the latest version of compiler-builtins. If this problem still occurs, please show the error message that indicates which function is calling panic.

[tmiasko]

Testing with compiler-builtins 0.1.68, the original steps still reproduce the issue for me. Panics originate from arithmetic operations that perform overflow checks:

error: linking with `cc` failed: exit status: 1
  |
  = note: "cc" "-m64" "/tmp/a/target/x86_64-unknown-linux-gnu/debug/deps/a-67c5d10adbae7870.std-5f98db226bab3e6c.std.dd5d69d6-cgu.0.rcgu.o.rcgu.o" "-Wl,--as-needed" "-L" "/tmp/a/target/x86_64-unknown-linux-gnu/debug/deps" "-L" "/tmp/a/target/debug/deps" "-L" "/home/../rust/build/x86_64-unknown-linux-gnu/stage1/lib/rustlib/x86_64-unknown-linux-gnu/lib" "-Wl,--start-group" "-Wl,--end-group" "-Wl,-Bstatic" "/tmp/a/target/x86_64-unknown-linux-gnu/debug/deps/libcompiler_builtins-89ced71a6bca4a7c.rlib" "-Wl,-Bdynamic" "-lgcc_s" "-lutil" "-lrt" "-lpthread" "-lm" "-ldl" "-lc" "-Wl,--eh-frame-hdr" "-Wl,-znoexecstack" "-L" "/home/../rust/build/x86_64-unknown-linux-gnu/stage1/lib/rustlib/x86_64-unknown-linux-gnu/lib" "-o" "/tmp/a/target/x86_64-unknown-linux-gnu/debug/deps/a-67c5d10adbae7870" "-Wl,--gc-sections" "-pie" "-Wl,-zrelro,-znow" "-nodefaultlibs"
  = note: /usr/bin/ld: /tmp/a/target/x86_64-unknown-linux-gnu/debug/deps/libcompiler_builtins-89ced71a6bca4a7c.rlib(compiler_builtins-89ced71a6bca4a7c.compiler_builtins.1a0b759d-cgu.14.rcgu.o): in function `<u128 as core::ops::arith::Add>::add':
          /home/../rust/build/x86_64-unknown-linux-gnu/stage1/lib/rustlib/src/rust/library/core/src/ops/arith.rs:126: undefined reference to `core::panicking::panic'
          /usr/bin/ld: /tmp/a/target/x86_64-unknown-linux-gnu/debug/deps/libcompiler_builtins-89ced71a6bca4a7c.rlib(compiler_builtins-89ced71a6bca4a7c.compiler_builtins.1a0b759d-cgu.14.rcgu.o): in function `<i16 as core::ops::arith::Sub>::sub':
          /home/../rust/build/x86_64-unknown-linux-gnu/stage1/lib/rustlib/src/rust/library/core/src/ops/arith.rs:233: undefined reference to `core::panicking::panic'
          /usr/bin/ld: /tmp/a/target/x86_64-unknown-linux-gnu/debug/deps/libcompiler_builtins-89ced71a6bca4a7c.rlib(compiler_builtins-89ced71a6bca4a7c.compiler_builtins.1a0b759d-cgu.14.rcgu.o): in function `<u128 as core::ops::arith::AddAssign>::add_assign':
          /home/../rust/build/x86_64-unknown-linux-gnu/stage1/lib/rustlib/src/rust/library/core/src/ops/arith.rs:779: undefined reference to `core::panicking::panic'
          /usr/bin/ld: /tmp/a/target/x86_64-unknown-linux-gnu/debug/deps/libcompiler_builtins-89ced71a6bca4a7c.rlib(compiler_builtins-89ced71a6bca4a7c.compiler_builtins.1a0b759d-cgu.14.rcgu.o): in function `<i16 as core::ops::arith::SubAssign>::sub_assign':
          /home/../rust/build/x86_64-unknown-linux-gnu/stage1/lib/rustlib/src/rust/library/core/src/ops/arith.rs:846: undefined reference to `core::panicking::panic'
          /usr/bin/ld: /tmp/a/target/x86_64-unknown-linux-gnu/debug/deps/libcompiler_builtins-89ced71a6bca4a7c.rlib(compiler_builtins-89ced71a6bca4a7c.compiler_builtins.1a0b759d-cgu.7.rcgu.o): in function `compiler_builtins::int::specialized_div_rem::u128_div_rem':
          /home/../.cargo/registry/src/github.com-1ecc6299db9ec823/compiler_builtins-0.1.68/src/int/specialized_div_rem/asymmetric.rs:51: undefined reference to `core::panicking::panic'
          /usr/bin/ld: /tmp/a/target/x86_64-unknown-linux-gnu/debug/deps/libcompiler_builtins-89ced71a6bca4a7c.rlib(compiler_builtins-89ced71a6bca4a7c.compiler_builtins.1a0b759d-cgu.7.rcgu.o):/home/../.cargo/registry/src/github.com-1ecc6299db9ec823/compiler_builtins-0.1.68/src/int/specialized_div_rem/asymmetric.rs:52: more undefined references to `core::panicking::panic' follow
          collect2: error: ld returned 1 exit status
          
  = help: some `extern` functions couldn't be found; some native libraries may need to be installed or have their path specified
  = note: use the `-l` flag to specify native libraries to link
  = note: use the `cargo:rustc-link-lib` directive to specify the native libraries to link with Cargo (see https://doc.rust-lang.org/cargo/reference/build-scripts.html#cargorustc-link-libkindname)