[wasm32-unknown-emscripten] undefined symbols: longjmp, setjmp

[ahaoboy]

When the target is wasm32-unknown-emscripten, unable to find symbols: longjmp, setjmp, setjmp-longjmp support is enabled by default in Emscripten.
https://emscripten.org/docs/porting/setjmp-longjmp.html

I tried this code:

use ::libc;
extern "C" {
    fn printf(_: *const libc::c_char, _: ...) -> libc::c_int;
    fn setjmp(_: *mut libc::c_void) -> libc::c_int;
    fn longjmp(_: *mut libc::c_void, _: libc::c_int) -> !;
}


pub static mut exception_buffer: [u8; 100] = [0u8; 100];

pub unsafe extern "C" fn do_something(value: libc::c_int) {
    if value < 0 as libc::c_int {
        printf(
            b"do_something: Error! Value cannot be negative.\n\0" as *const u8
                as *const libc::c_char,
        );
        longjmp(
            exception_buffer.as_mut_ptr() as *mut libc::c_void,
            1 as libc::c_int,
        );
    }
    printf(
        b"do_something: Value is %d\n\0" as *const u8 as *const libc::c_char,
        value,
    );
}
fn main() {
    unsafe {
        let value: libc::c_int = -(5 as libc::c_int);
        if setjmp(exception_buffer.as_mut_ptr() as *mut libc::c_void) == 0 as libc::c_int {
            printf(
                b"Main: Setting up exception handling...\n\0" as *const u8 as *const libc::c_char,
            );
            do_something(value);
        } else {
            printf(b"Main: Handling exception...\n\0" as *const u8 as *const libc::c_char);
        }
        printf(
            b"Main: Program continues after exception handling.\n\0" as *const u8
                as *const libc::c_char,
        );
    }
}

I expected to see this happen: explanation
cargo run

Main: Setting up exception handling...
do_something: Error! Value cannot be negative.
Main: Handling exception...
Main: Program continues after exception handling.

Instead, this happened: explanation
cargo run --target=wasm32-unknown-emscripten

  = note: wasm-ld: error: /root/ct/wasm32-unknown-emscripten/debug/deps/emsdk_demo.5eeji6ymekqs85b7.rcgu.o: undefined symbol: longjmp
          wasm-ld: error: /root/ct/wasm32-unknown-emscripten/debug/deps/emsdk_demo.5eeji6ymekqs85b7.rcgu.o: undefined symbol: setjmp

Meta

rustc --version --verbose:

rustc 1.76.0-nightly (2b603f95a 2023-11-12)
binary: rustc
commit-hash: 2b603f95a48f10f931a61dd208fe3e5ffd64e491
commit-date: 2023-11-12
host: x86_64-unknown-linux-gnu
release: 1.76.0-nightly
LLVM version: 17.0.4


rustc 1.74.0 (79e9716c9 2023-11-13)
binary: rustc
commit-hash: 79e9716c980570bfd1f666e3b16ac583f0168962
commit-date: 2023-11-13
host: x86_64-unknown-linux-gnu
release: 1.74.0
LLVM version: 17.0.4

Backtrace

RUST_BACKTRACE=1 cargo build --target=wasm32-unknown-emscripten#                                                                                                            
u23#  RUST_BACKTRACE=1 cargo build --target=wasm32-unknown-emscripten
   Compiling emsdk-demo v0.1.0 (/root/code/emsdk-demo)
warning: static variable `exception_buffer` should have an upper case name
 --> src/main.rs:9:16
  |
9 | pub static mut exception_buffer: [u8; 100] = [0u8; 100];
  |                ^^^^^^^^^^^^^^^^ help: convert the identifier to upper case: `EXCEPTION_BUFFER`
  |
  = note: `#[warn(non_upper_case_globals)]` on by default

error: linking with `emcc` failed: exit status: 1
  |
  = note: LC_ALL="C" PATH="/root/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/x86_64-unknown-linux-gnu/bin:/root/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/x86_64-unknown-linux-gnu/bin/self-contained:/root/code/emsdk:/root/code/emsdk/upstream/emscripten:/run/user/0/fnm_multishells/51368_1701605570612/bin:/root/.vscode-server/bin/1a5daa3a0231a0fbba4f14db7ec463cf99d7768e/bin/remote-cli:/root/.local/share/pnpm:/root/.cargo/bin:/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin:/usr/games:/usr/local/games:/snap/bin" VSLANG="1033" "emcc" "-s" "EXPORTED_FUNCTIONS=[\"_main\"]" "/root/ct/wasm32-unknown-emscripten/debug/deps/emsdk_demo.1wof4idzl24j4p0a.rcgu.o" "/root/ct/wasm32-unknown-emscripten/debug/deps/emsdk_demo.2nt1liv8b0dfeizm.rcgu.o" "/root/ct/wasm32-unknown-emscripten/debug/deps/emsdk_demo.43djbu2r1eeqpn12.rcgu.o" "/root/ct/wasm32-unknown-emscripten/debug/deps/emsdk_demo.5eeji6ymekqs85b7.rcgu.o" "/root/ct/wasm32-unknown-emscripten/debug/deps/emsdk_demo.vg9f46yl3mh9xiu.rcgu.o" "/root/ct/wasm32-unknown-emscripten/debug/deps/emsdk_demo.2t7mycb9l7k0tgy.rcgu.o" "-L" "/root/ct/wasm32-unknown-emscripten/debug/deps" "-L" "/root/ct/debug/deps" "-L" "/root/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/wasm32-unknown-emscripten/lib" "/root/ct/wasm32-unknown-emscripten/debug/deps/liblibc-9bc98c84e1a910dc.rlib" "/root/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/wasm32-unknown-emscripten/lib/libstd-61e93cdfb239f7c2.rlib" "/root/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/wasm32-unknown-emscripten/lib/libpanic_unwind-c51bd600d3569b2d.rlib" "/root/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/wasm32-unknown-emscripten/lib/librustc_demangle-8e67090878f28f69.rlib" "/root/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/wasm32-unknown-emscripten/lib/libstd_detect-3fb9a4c301477b79.rlib" "/root/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/wasm32-unknown-emscripten/lib/libhashbrown-5c1b3f61e45e4bf0.rlib" "/root/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/wasm32-unknown-emscripten/lib/librustc_std_workspace_alloc-f99cb7d3c28bae00.rlib" "/root/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/wasm32-unknown-emscripten/lib/libminiz_oxide-942831f28a82cd36.rlib" "/root/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/wasm32-unknown-emscripten/lib/libadler-8e620a0166013244.rlib" "/root/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/wasm32-unknown-emscripten/lib/libunwind-b17b8f660cd36185.rlib" "/root/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/wasm32-unknown-emscripten/lib/libcfg_if-0c7bacfbf87cda18.rlib" "/root/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/wasm32-unknown-emscripten/lib/liblibc-48b2b822b890a628.rlib" "/root/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/wasm32-unknown-emscripten/lib/liballoc-e119f963323764f2.rlib" "/root/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/wasm32-unknown-emscripten/lib/librustc_std_workspace_core-dccfe230458f39f9.rlib" "/root/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/wasm32-unknown-emscripten/lib/libcore-ff850c1994b8a1ec.rlib" "/root/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/wasm32-unknown-emscripten/lib/libcompiler_builtins-295fcaa60ab90f2f.rlib" "-l" "c" "-B/root/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/x86_64-unknown-linux-gnu/bin/gcc-ld" "-fuse-ld=lld" "--target=wasm32-unknown-emscripten" "-s" "DISABLE_EXCEPTION_CATCHING=0" "-L" "/root/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/wasm32-unknown-emscripten/lib" "-L" "/root/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/wasm32-unknown-emscripten/lib/self-contained" "-o" "/root/ct/wasm32-unknown-emscripten/debug/deps/emsdk_demo.js" "-O0" "-g" "-sABORTING_MALLOC=0" "-Wl,--fatal-warnings"
  = note: wasm-ld: error: /root/ct/wasm32-unknown-emscripten/debug/deps/emsdk_demo.5eeji6ymekqs85b7.rcgu.o: undefined symbol: longjmp
          wasm-ld: error: /root/ct/wasm32-unknown-emscripten/debug/deps/emsdk_demo.5eeji6ymekqs85b7.rcgu.o: undefined symbol: setjmp
          emcc: error: '/root/code/emsdk/upstream/bin/wasm-ld -o /root/ct/wasm32-unknown-emscripten/debug/deps/emsdk_demo.wasm /root/ct/wasm32-unknown-emscripten/debug/deps/emsdk_demo.1wof4idzl24j4p0a.rcgu.o /root/ct/wasm32-unknown-emscripten/debug/deps/emsdk_demo.2nt1liv8b0dfeizm.rcgu.o /root/ct/wasm32-unknown-emscripten/debug/deps/emsdk_demo.43djbu2r1eeqpn12.rcgu.o /root/ct/wasm32-unknown-emscripten/debug/deps/emsdk_demo.5eeji6ymekqs85b7.rcgu.o /root/ct/wasm32-unknown-emscripten/debug/deps/emsdk_demo.vg9f46yl3mh9xiu.rcgu.o /root/ct/wasm32-unknown-emscripten/debug/deps/emsdk_demo.2t7mycb9l7k0tgy.rcgu.o -L/root/ct/wasm32-unknown-emscripten/debug/deps -L/root/ct/debug/deps -L/root/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/wasm32-unknown-emscripten/lib /root/ct/wasm32-unknown-emscripten/debug/deps/liblibc-9bc98c84e1a910dc.rlib /root/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/wasm32-unknown-emscripten/lib/libstd-61e93cdfb239f7c2.rlib /root/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/wasm32-unknown-emscripten/lib/libpanic_unwind-c51bd600d3569b2d.rlib /root/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/wasm32-unknown-emscripten/lib/librustc_demangle-8e67090878f28f69.rlib /root/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/wasm32-unknown-emscripten/lib/libstd_detect-3fb9a4c301477b79.rlib /root/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/wasm32-unknown-emscripten/lib/libhashbrown-5c1b3f61e45e4bf0.rlib /root/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/wasm32-unknown-emscripten/lib/librustc_std_workspace_alloc-f99cb7d3c28bae00.rlib /root/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/wasm32-unknown-emscripten/lib/libminiz_oxide-942831f28a82cd36.rlib /root/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/wasm32-unknown-emscripten/lib/libadler-8e620a0166013244.rlib /root/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/wasm32-unknown-emscripten/lib/libunwind-b17b8f660cd36185.rlib /root/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/wasm32-unknown-emscripten/lib/libcfg_if-0c7bacfbf87cda18.rlib /root/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/wasm32-unknown-emscripten/lib/liblibc-48b2b822b890a628.rlib /root/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/wasm32-unknown-emscripten/lib/liballoc-e119f963323764f2.rlib /root/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/wasm32-unknown-emscripten/lib/librustc_std_workspace_core-dccfe230458f39f9.rlib /root/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/wasm32-unknown-emscripten/lib/libcore-ff850c1994b8a1ec.rlib /root/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/wasm32-unknown-emscripten/lib/libcompiler_builtins-295fcaa60ab90f2f.rlib -lc-debug -L/root/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/wasm32-unknown-emscripten/lib -L/root/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/wasm32-unknown-emscripten/lib/self-contained --fatal-warnings -L/root/code/emsdk/upstream/emscripten/cache/sysroot/lib/wasm32-emscripten -lGL -lal -lhtml5 -lstubs-debug -lnoexit -lc-debug -ldlmalloc -lcompiler_rt -lc++ -lc++abi-debug -lsockets -mllvm -combiner-global-alias-analysis=false -mllvm -enable-emscripten-cxx-exceptions -mllvm -enable-emscripten-sjlj -mllvm -disable-lsr /tmp/tmpg1ciymx5libemscripten_js_symbols.so --export-if-defined=main --export-if-defined=__get_exception_message --export-if-defined=free --export-if-defined=__start_em_asm --export-if-defined=__stop_em_asm --export-if-defined=__start_em_lib_deps --export-if-defined=__stop_em_lib_deps --export-if-defined=__start_em_js --export-if-defined=__stop_em_js --export-if-defined=__main_argc_argv --export-if-defined=fflush --export=emscripten_stack_get_end --export=emscripten_stack_get_free --export=emscripten_stack_get_base --export=emscripten_stack_get_current --export=emscripten_stack_init --export=stackSave --export=stackRestore --export=stackAlloc --export=__errno_location --export=__get_temp_ret --export=__set_temp_ret --export=__cxa_is_pointer_type --export=__cxa_can_catch --export=__cxa_increment_exception_refcount --export=__cxa_decrement_exception_refcount --export=setThrew --export=__cxa_free_exception --export=__wasm_call_ctors --export=__get_exception_message --export=free --export-table -z stack-size=65536 --initial-memory=16777216 --max-memory=16777216 --no-entry --stack-first --table-base=1' failed (returned 1)
          

warning: `emsdk-demo` (bin "emsdk-demo") generated 1 warning
error: could not compile `emsdk-demo` (bin "emsdk-demo") due to previous error; 1 warning emitted```

</p>
</details>

[bjorn3]

setjmp and longjmp look to be defined by the javascript side rather than the wasm side. By default any function undefined on the wasm side will result in a linker error. Emscripten passes a list of symbols to import from javascript to the linker, but maybe setjmp and longjmp are missing from this list? You can try passing -Clink-arg=-Wl,--import-undefined to rustc.

[ahaoboy]

setjmp and longjmp look to be defined by the javascript side rather than the wasm side. By default any function undefined on the wasm side will result in a linker error. Emscripten passes a list of symbols to import from javascript to the linker, but maybe setjmp and longjmp are missing from this list? You can try passing -Clink-arg=-Wl,--import-undefined to rustc.

The longjmp and setjmp are c functiion

emcc ./main.c -s ENVIRONMENT='node' -o main.js
node ./main.js
outpu:
Main: Setting up exception handling...
do_something: Error! Value cannot be negative.
Main: Handling exception...
Main: Program continues after exception handling.

#include <stdio.h>
#include <setjmp.h>

jmp_buf exception_buffer;

void do_something(int value)
{
  if (value < 0)
  {
    printf("do_something: Error! Value cannot be negative.\n");
    longjmp(exception_buffer, 1); // Jump back to the setjmp point with a return value of 1
  }

  printf("do_something: Value is %d\n", value);
}

int main()
{
  int value = -5;

  if (setjmp(exception_buffer) == 0)
  {
    // Program execution enters here when setjmp is first called
    printf("Main: Setting up exception handling...\n");
    do_something(value); // Call a function that may longjmp in case of an error
  }
  else
  {
    // Program execution enters here if longjmp was called
    printf("Main: Handling exception...\n");
  }

  printf("Main: Program continues after exception handling.\n");
  return 0;
}
// emcc ./main.c -s ENVIRONMENT='node' -o main.js

[bjorn3]

The actual implementation is in javascript using javascript exceptions by default unless you enable the option to use wasm exceptions instead.

[ahaoboy]

The actual implementation is in javascript using javascript exceptions by default unless you enable the option to use wasm exceptions instead.

The issue is that compiling with the default parameters using emcc is successful, but executing with Cargo's default parameters results in an error. Could this inconsistency be due to Cargo passing different default parameters than emcc?

// both are ok
 emcc ./main.c -s ENVIRONMENT='web,node' -o main.js
 emcc ./main.c -o main.js

// error
cargo run --target=wasm32-unknown-emscripten

[bjorn3]

Rustc passes -Wl,--fatal-warnings and -sABORTING_MALLOC=0 to emcc. There is no other difference that I can tell.

[ahaoboy]

Rustc passes -Wl,--fatal-warnings and -sABORTING_MALLOC=0 to emcc. There is no other difference that I can tell.

I tried to manually add these parameters -Wl,--fatal-warnings -s ABORTING_MALLOC=0 . Although they can compile, there is a runtime error RuntimeError: Aborted(missing function: setjmp) when running, but emcc can compile and run.

 emcc --version
emcc (Emscripten gcc/clang-like replacement + linker emulating GNU ld) 3.1.50 (047b82506d6b471873300a5e4d1e690420b582d0)
Copyright (C) 2014 the Emscripten authors (see AUTHORS.txt)
This is free and open source software under the MIT license.
There is NO warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.