strict.test_atexit_standalone regression: "undefined symbol: __syscall_pause"

[juj]

After PR #26860

commit 4bf5fb7a35c38935d20c6f8a7e3a3f1153932758
Author: Kleis Auke Wolthuizen <github@kleisauke.nl>
Date:   Thu May 21 22:24:38 2026 +0200

    Update musl to v1.2.6 (#26860)

test strict.test_atexit_standalone fails with

C:\emsdk\emscripten\main>test\runner strict.test_atexit_standalone
Running 1 tests
[1/1] test_atexit_standalone (test_core.strict.test_atexit_standalone) ... FAIL

Stdout:
wasm-ld: error: C:\emsdk\emscripten\main\cache\sysroot\lib\wasm32-emscripten\libstandalonewasm-nocatch-pure.a(exit.o): undefined symbol: __syscall_pause
emcc: error: ''C:/emsdk/llvm/git/build_main_vs2022_64/Release/bin\wasm-ld.exe' -o test_atexit.wasm 'C:\Users\clb\AppData\Local\Temp\tmp1dpzghcilibemscripten_js_symbols.so' --strip-debug --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-table -z stack-size=65536 --no-growable-memory --initial-heap=16777216 --stack-first --table-base=1 'C:\Users\clb\AppData\Local\Temp\emscripten_temp_3q07pvdp\test_atexit.o' '-LC:\emsdk\emscripten\main\cache\sysroot\lib\wasm32-emscripten' '-LC:\emsdk\emscripten\main\src\lib' 'C:\emsdk\emscripten\main\cache\sysroot\lib\wasm32-emscripten\crt1.o' -lstandalonewasm-nocatch-pure -lc-debug -ldlmalloc-debug -lcompiler_rt -lsockets --fatal-warnings -mllvm -combiner-global-alias-analysis=false -mllvm -disable-lsr' failed (returned 1)

None


======================================================================
FAIL: test_atexit_standalone (test_core.strict.test_atexit_standalone)
----------------------------------------------------------------------
Traceback (most recent call last):
  File "C:\emsdk\emscripten\main\test\common.py", line 1213, in run_process
    rtn = utils.run_process(cmd, check=check, **kwargs)
  File "C:\emsdk\emscripten\main\tools\utils.py", line 45, in run_process
    ret = subprocess.run(cmd, check=check, input=input, *args, **kw)
  File "C:\emsdk\python\3.13.3_64bit\Lib\subprocess.py", line 577, in run
    raise CalledProcessError(retcode, process.args,
                             output=stdout, stderr=stderr)
subprocess.CalledProcessError: Command '['C:\\emsdk\\emscripten\\main\\emcc.bat', 'C:\\emsdk\\emscripten\\main\\test\\core\\test_atexit.c', '-o', 'test_atexit.js', '-sNO_DEFAULT_TO_CXX', '-sSTRICT', '-sSTANDALONE_WASM', '-sPURE_WASI', '-Wclosure', '-Werror', '-Wno-limited-postlink-optimizations', '-Wno-unused-command-line-argument', '-Wno-unused-command-line-argument']' returned non-zero exit status 1.

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "C:\emsdk\emscripten\main\test\common.py", line 380, in resulting_test
    return func(self, *args)
  File "C:\emsdk\emscripten\main\test\decorators.py", line 496, in metafunc
    return func(self, *args, **kwargs)
  File "C:\emsdk\emscripten\main\test\test_core.py", line 2540, in test_atexit
    self.do_core_test('test_atexit.c')
    ~~~~~~~~~~~~~~~~~^^^^^^^^^^^^^^^^^
  File "C:\emsdk\emscripten\main\test\test_core.py", line 501, in do_core_test
    self.do_run_in_out_file_test(Path('core', testname), **kwargs)
    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "C:\emsdk\emscripten\main\test\common.py", line 1404, in do_run_in_out_file_test
    output = self._build_and_run(srcfile, expected, **kwargs)
  File "C:\emsdk\emscripten\main\test\common.py", line 1423, in _build_and_run
    js_file = self.build(filename, **kwargs)
  File "C:\emsdk\emscripten\main\test\common.py", line 913, in build
    self.run_process(cmd, stderr=self.stderr_redirect if not DEBUG else None)
    ~~~~~~~~~~~~~~~~^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "C:\emsdk\emscripten\main\test\common.py", line 1218, in run_process
    self.fail(f'subprocess exited with non-zero return code({e.returncode}): `{shlex.join(cmd)}`')
    ~~~~~~~~~^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
AssertionError: subprocess exited with non-zero return code(1): `'C:\emsdk\emscripten\main\emcc.bat' 'C:\emsdk\emscripten\main\test\core\test_atexit.c' -o test_atexit.js -sNO_DEFAULT_TO_CXX -sSTRICT -sSTANDALONE_WASM -sPURE_WASI -Wclosure -Werror -Wno-limited-postlink-optimizations -Wno-unused-command-line-argument -Wno-unused-command-line-argument`

Stdout:
wasm-ld: error: C:\emsdk\emscripten\main\cache\sysroot\lib\wasm32-emscripten\libstandalonewasm-nocatch-pure.a(exit.o): undefined symbol: __syscall_pause
emcc: error: ''C:/emsdk/llvm/git/build_main_vs2022_64/Release/bin\wasm-ld.exe' -o test_atexit.wasm 'C:\Users\clb\AppData\Local\Temp\tmp1dpzghcilibemscripten_js_symbols.so' --strip-debug --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-table -z stack-size=65536 --no-growable-memory --initial-heap=16777216 --stack-first --table-base=1 'C:\Users\clb\AppData\Local\Temp\emscripten_temp_3q07pvdp\test_atexit.o' '-LC:\emsdk\emscripten\main\cache\sysroot\lib\wasm32-emscripten' '-LC:\emsdk\emscripten\main\src\lib' 'C:\emsdk\emscripten\main\cache\sysroot\lib\wasm32-emscripten\crt1.o' -lstandalonewasm-nocatch-pure -lc-debug -ldlmalloc-debug -lcompiler_rt -lsockets --fatal-warnings -mllvm -combiner-global-alias-analysis=false -mllvm -disable-lsr' failed (returned 1)

None

----------------------------------------------------------------------
Ran 1 test in 0.472s

FAILED (failures=1)

C:\emsdk\emscripten\main>

[sbc100]

@kleisauke should we maybe create a real version of __syscall_pause? Or maybe just remove its usage from system/lib/libc/musl/src/exit/exit.c?

[kleisauke]

I think it might be easier to stub the pause() syscall in standalone mode, similar to how we handle it in libstubs (which is disabled by -sSTRICT, since that mode builds with -sALLOW_UNIMPLEMENTED_SYSCALLS=0).

I've just opened PR #27038 to address this. Thanks for reporting!