Undefined reference to `_Unwind_Resume`

[jefftime]

I tried to compile a no_std project with Rust, but setting the eh_unwind_resume lang_item does not seem to work properly. Building in release with cargo or -O with rustc works properly, but a debug build fails with an undefined reference to '_Unwind_Resume'.

Here is the code I tried to get working.

rustc --version --verbose:

rustc 1.25.0-nightly (e6072a7b3 2018-01-13)
binary: rustc
commit-hash: e6072a7b3835f1875e81c9fd27799f9b20a0770c
commit-date: 2018-01-13
host: x86_64-unknown-linux-gnu
release: 1.25.0-nightly
LLVM version: 4.0

[steveklabnik]

We had talked on Hacker News, and while this version compiles for me, it doesn't seem to for @jefftime

https://gist.github.com/steveklabnik/5abd59a8fe7e5abda3db58bd8c208fbb

[hanna-kruppe]

Seems similar to #47442. As mentioned there, projects that don't want unwinding need to compile with panic=abort to work reliably.

[jefftime]

Neither setting panic=abort nor specifying the eh_personality, eh_unwind_resume, and panic_fmt lang_items successfully compile with debug settings for me

[FenrirWolf]

Even when you recompile core via xargo?

[pietroalbini]

Might this be related with #47551?

[bossmc]

@pietroalbini Probably not, in that case the link is fine, but the generated binary is broken.

This also fails to link for me (rustc 1.25.0-nightly (79a521b 2018-01-15)) with:

Error: linking with `cc` failed: exit code: 1
  |
  = note: "cc" "-Wl,--as-needed" "-Wl,-z,noexecstack" "-m64" "-L" "/home/andy/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/x86_64-unknown-linux-gnu/lib" "test.test0.rcgu.o" "test.test1.rcgu.o" "test.test2.rcgu.o" "-o" "test" "-Wl,--gc-sections" "-pie" "-Wl,-z,relro,-z,now" "-nodefaultlibs" "-L" "/home/andy/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/x86_64-unknown-linux-gnu/lib" "-l" "c" "-Wl,-Bstatic" "/home/andy/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/x86_64-unknown-linux-gnu/lib/libcore-9d4b7130b0117f1c.rlib" "-Wl,-Bdynamic"
  = note: test.test0.rcgu.o: In function `_$LT$core..result..Result$LT$T$C$$u20$E$GT$$GT$::unwrap::h4cfe66017ee4cfbf':
          test0-317d481089b8c8fe83113de504472633.rs:(.text._ZN47_$LT$core..result..Result$LT$T$C$$u20$E$GT$$GT$6unwrap17h4cfe66017ee4cfbfE+0x3d): undefined reference to `_Unwind_Resume'
          test.test0.rcgu.o: In function `core::result::unwrap_failed::h8821e290e357350d':
          test0-317d481089b8c8fe83113de504472633.rs:(.text._ZN4core6result13unwrap_failed17h8821e290e357350dE+0x95): undefined reference to `_Unwind_Resume'
          collect2: error: ld returned 1 exit status

If I add -l gcc_s (since the glibc unwinding implementation is in libgcc_s) to the link command it links and runs correctly. Either:

• Result's [no_std] implementation is wrong to assume libgcc_s will be present to provide unwinding support
• The [no_std] link commands are wrong to not include libgcc_s on the XXX-unknown-linux-gnu target

Attempting to build against x86_64-unknown-linux-musl suggests it's the former, that build also fails with a much longer link failure (longer, but still all about _Unwind_XXX functions).

[bossmc]

Ah, sorry, my analysis at the end there is bogus, the #[lang = "eh_unwind_resume"] function is supposed to be used in place of the "default" implementation (which is just extern-ing a rust_eh_unwind_resume). See

rust/src/librustc_trans/context.rs

Lines 395 to 422 in da569fa

	pub fn eh_unwind_resume(&self) -> ValueRef {
	use attributes;
	let unwresume = &self.eh_unwind_resume;
	if let Some(llfn) = unwresume.get() {
	return llfn;
	}
	let tcx = self.tcx;
	assert!(self.sess().target.target.options.custom_unwind_resume);
	if let Some(def_id) = tcx.lang_items().eh_unwind_resume() {
	let llfn = callee::resolve_and_get_fn(self, def_id, tcx.intern_substs(&[]));
	unwresume.set(Some(llfn));
	return llfn;
	}
	let ty = tcx.mk_fn_ptr(ty::Binder(tcx.mk_fn_sig(
	iter::once(tcx.mk_mut_ptr(tcx.types.u8)),
	tcx.types.never,
	false,
	hir::Unsafety::Unsafe,
	Abi::C
	)));
	let llfn = declare::declare_fn(self, "rust_eh_unwind_resume", ty);
	attributes::unwind(llfn, true);
	unwresume.set(Some(llfn));
	llfn
	}

.

[glandium]

Today I've hit the same error with the following:

#![no_std]
#![no_main]
#![feature(lang_items)]
#[link(name="c")]
extern "C" {}

#[lang = "panic_fmt"]
#[no_mangle]
pub fn panic_fmt(_: core::fmt::Arguments, _: &'static str, _: u32, _: u32) -> ! {
    loop {}
}

#[no_mangle]
pub extern "C" fn main(_argc: isize, _arg: *const *const u8) -> isize {
    let a: Result<(), usize> = Err(42);
    a.unwrap();
    0
}

And with the following added to the corresponding Cargo.toml:

[profile.release]
panic="abort"

[profile.dev]
panic="abort"

The above fails to build with cargo +nightly build but builds fine with cargo +nightly build --release. x86_64-unknown-linux-gnu target.

[glandium]

FWIW, when looking at the llvm-ir emitted for unwrap_failed, with opt-level=0, I can see multiple to label %somelabel unwind label %cleanup, but there are none with opt-level=1. They seem to correspond to the assembly calling _Unwind_Resume.

[hadronized]

Hello. I have a similar issue there.

Code here.