PRINTF_LONG_DOUBLE is not compatible with MAIN_MODULE

[allsey87]

Version of emscripten/emsdk:

root@576256f6896e:/src# emcc -v
emcc (Emscripten gcc/clang-like replacement + linker emulating GNU ld) 3.1.61 (67fa4c16496b157a7fc3377afd69ee0445e8a6e3)
clang version 19.0.0git (https:/github.com/llvm/llvm-project 7cfffe74eeb68fbb3fb9706ac7071f8caeeb6520)
Target: wasm32-unknown-emscripten
Thread model: posix
InstalledDir: /emsdk/upstream/bin

Failing command line in full:
emcc test.c -sPRINTF_LONG_DOUBLE=1 -sMAIN_MODULE

Contents of test.c:

#include <stdio.h>

int main() {
    printf("Hello, World!");
    return 0;
}

Full link command and output with -v appended:

root@576256f6896e:/src# emcc test.c -sPRINTF_LONG_DOUBLE=1 -sMAIN_MODULE -v
 /emsdk/upstream/bin/clang -target wasm32-unknown-emscripten -fignore-exceptions -fPIC -fvisibility=default -mllvm -combiner-global-alias-analysis=false -mllvm -enable-emscripten-sjlj -mllvm -disable-lsr --sysroot=/emsdk/upstream/emscripten/cache/sysroot -DEMSCRIPTEN -Werror=implicit-function-declaration -Xclang -iwithsysroot/include/fakesdl -Xclang -iwithsysroot/include/compat -v test.c -c -o /tmp/emscripten_temp_pbobb795/test_0.o
clang version 19.0.0git (https:/github.com/llvm/llvm-project 7cfffe74eeb68fbb3fb9706ac7071f8caeeb6520)
Target: wasm32-unknown-emscripten
Thread model: posix
InstalledDir: /emsdk/upstream/bin
 (in-process)
 "/emsdk/upstream/bin/clang-19" -cc1 -triple wasm32-unknown-emscripten -emit-obj -disable-free -clear-ast-before-backend -disable-llvm-verifier -discard-value-names -main-file-name test.c -mrelocation-model pic -pic-level 2 -mframe-pointer=none -ffp-contract=on -fno-rounding-math -mconstructor-aliases -target-feature +mutable-globals -target-cpu generic -debugger-tuning=gdb -fdebug-compilation-dir=/src -v -fcoverage-compilation-dir=/src -resource-dir /emsdk/upstream/lib/clang/19 -D EMSCRIPTEN -isysroot /emsdk/upstream/emscripten/cache/sysroot -internal-isystem /emsdk/upstream/lib/clang/19/include -internal-isystem /emsdk/upstream/emscripten/cache/sysroot/include/wasm32-emscripten -internal-isystem /emsdk/upstream/emscripten/cache/sysroot/include -Werror=implicit-function-declaration -ferror-limit 19 -fvisibility=default -fgnuc-version=4.2.1 -fskip-odr-check-in-gmf -fignore-exceptions -fcolor-diagnostics -iwithsysroot/include/fakesdl -iwithsysroot/include/compat -mllvm -combiner-global-alias-analysis=false -mllvm -enable-emscripten-sjlj -mllvm -disable-lsr -o /tmp/emscripten_temp_pbobb795/test_0.o -x c test.c
clang -cc1 version 19.0.0git based upon LLVM 19.0.0git default target x86_64-unknown-linux-gnu
ignoring nonexistent directory "/emsdk/upstream/emscripten/cache/sysroot/include/wasm32-emscripten"
#include "..." search starts here:
#include <...> search starts here:
 /emsdk/upstream/emscripten/cache/sysroot/include/fakesdl
 /emsdk/upstream/emscripten/cache/sysroot/include/compat
 /emsdk/upstream/lib/clang/19/include
 /emsdk/upstream/emscripten/cache/sysroot/include
End of search list.
 /emsdk/upstream/bin/clang --version
 /emsdk/upstream/bin/wasm-ld -o a.out.wasm /tmp/emscripten_temp_pbobb795/test_0.o -L/emsdk/upstream/emscripten/cache/sysroot/lib/wasm32-emscripten/pic -lGL-getprocaddr -lal -lhtml5 -lprintf_long_double-debug -lstubs-debug -lnoexit -lc-debug -ldlmalloc -lcompiler_rt -lc++-noexcept -lc++abi-debug-noexcept -lsockets -mllvm -combiner-global-alias-analysis=false -mllvm -enable-emscripten-sjlj -mllvm -disable-lsr --export-if-defined=setThrew --export-if-defined=_emscripten_stack_restore --export-if-defined=emscripten_stack_get_current --export-if-defined=_emscripten_tempret_set --export-if-defined=malloc --export-if-defined=_emscripten_stack_alloc --export-if-defined=_emscripten_tempret_get --export-if-defined=htons --export-if-defined=ntohs --export-if-defined=htonl --export-if-defined=_emscripten_timeout --export-if-defined=__cxa_is_pointer_type --export-if-defined=emscripten_stack_get_base --export-if-defined=emscripten_stack_get_end --export-if-defined=free --export-if-defined=__cxa_can_catch --export-if-defined=__cxa_increment_exception_refcount --export-if-defined=__cxa_decrement_exception_refcount --export-if-defined=fileno --export-if-defined=emscripten_builtin_memalign --export-if-defined=__dl_seterr --export-if-defined=memcmp --export-if-defined=memcpy --export-if-defined=__errno_location --export-if-defined=__cxa_demangle /tmp/tmpn5vhuwbslibemscripten_js_symbols.so --import-memory --strip-debug --export=emscripten_stack_get_end --export=emscripten_stack_get_free --export=emscripten_stack_get_base --export=emscripten_stack_get_current --export=emscripten_stack_set_limits --export=_emscripten_stack_alloc --export=__get_temp_ret --export=__set_temp_ret --export=__wasm_call_ctors --export=setThrew --export=_emscripten_stack_restore --export=_emscripten_tempret_set --export=malloc --export=_emscripten_tempret_get --export=htons --export=ntohs --export=htonl --export=_emscripten_timeout --export=__cxa_is_pointer_type --export=free --export=__cxa_can_catch --export=__cxa_increment_exception_refcount --export=__cxa_decrement_exception_refcount --export=fileno --export=emscripten_builtin_memalign --export=__dl_seterr --export=memcmp --export=memcpy --export=__errno_location --export=__cxa_demangle --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 --export-if-defined=__main_argc_argv --export-if-defined=__wasm_apply_data_relocs --export-if-defined=fflush --experimental-pic --unresolved-symbols=import-dynamic -pie --no-export-dynamic -z stack-size=65536 --no-growable-memory --initial-memory=16777216 --no-entry --stack-first
 /emsdk/upstream/bin/wasm-ld -o a.out.wasm --whole-archive /tmp/emscripten_temp_pbobb795/test_0.o -L/emsdk/upstream/emscripten/cache/sysroot/lib/wasm32-emscripten/pic -lGL-getprocaddr -lal -lhtml5 -lprintf_long_double-debug -lstubs-debug -lnoexit -lc-debug -ldlmalloc -lcompiler_rt -lc++-noexcept -lc++abi-debug-noexcept -lsockets --no-whole-archive -mllvm -combiner-global-alias-analysis=false -mllvm -enable-emscripten-sjlj -mllvm -disable-lsr --export-if-defined=setThrew --export-if-defined=_emscripten_stack_restore --export-if-defined=emscripten_stack_get_current --export-if-defined=_emscripten_tempret_set --export-if-defined=malloc --export-if-defined=_emscripten_stack_alloc --export-if-defined=_emscripten_tempret_get --export-if-defined=htons --export-if-defined=ntohs --export-if-defined=htonl --export-if-defined=_emscripten_timeout --export-if-defined=__cxa_is_pointer_type --export-if-defined=emscripten_stack_get_base --export-if-defined=emscripten_stack_get_end --export-if-defined=free --export-if-defined=__cxa_can_catch --export-if-defined=__cxa_increment_exception_refcount --export-if-defined=__cxa_decrement_exception_refcount --export-if-defined=fileno --export-if-defined=emscripten_builtin_memalign --export-if-defined=__dl_seterr --export-if-defined=memcmp --export-if-defined=memcpy --export-if-defined=__errno_location --export-if-defined=__cxa_demangle /tmp/tmpmzhuwxfwlibemscripten_js_symbols.so --import-memory --strip-debug --export-dynamic --export=emscripten_stack_get_end --export=emscripten_stack_get_free --export=emscripten_stack_get_base --export=emscripten_stack_get_current --export=emscripten_stack_set_limits --export=_emscripten_stack_alloc --export=__get_temp_ret --export=__set_temp_ret --export=__wasm_call_ctors --export=setThrew --export=_emscripten_stack_restore --export=_emscripten_tempret_set --export=malloc --export=_emscripten_tempret_get --export=htons --export=ntohs --export=htonl --export=_emscripten_timeout --export=__cxa_is_pointer_type --export=free --export=__cxa_can_catch --export=__cxa_increment_exception_refcount --export=__cxa_decrement_exception_refcount --export=fileno --export=emscripten_builtin_memalign --export=__dl_seterr --export=memcmp --export=memcpy --export=__errno_location --export=__cxa_demangle --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 --export-if-defined=__main_argc_argv --export-if-defined=__wasm_apply_data_relocs --export-if-defined=fflush --experimental-pic --unresolved-symbols=import-dynamic -pie -z stack-size=65536 --no-growable-memory --initial-memory=16777216 --no-entry --stack-first
wasm-ld: error: duplicate symbol: __vfprintf_internal
>>> defined in /emsdk/upstream/emscripten/cache/sysroot/lib/wasm32-emscripten/pic/libprintf_long_double-debug.a(vfprintf.o)
>>> defined in /emsdk/upstream/emscripten/cache/sysroot/lib/wasm32-emscripten/pic/libc-debug.a(vfprintf.o)

wasm-ld: error: duplicate symbol: vfprintf
>>> defined in /emsdk/upstream/emscripten/cache/sysroot/lib/wasm32-emscripten/pic/libprintf_long_double-debug.a(vfprintf.o)
>>> defined in /emsdk/upstream/emscripten/cache/sysroot/lib/wasm32-emscripten/pic/libc-debug.a(vfprintf.o)

wasm-ld: error: duplicate symbol: vfiprintf
>>> defined in /emsdk/upstream/emscripten/cache/sysroot/lib/wasm32-emscripten/pic/libprintf_long_double-debug.a(vfprintf.o)
>>> defined in /emsdk/upstream/emscripten/cache/sysroot/lib/wasm32-emscripten/pic/libc-debug.a(vfprintf.o)

wasm-ld: error: duplicate symbol: __small_vfprintf
>>> defined in /emsdk/upstream/emscripten/cache/sysroot/lib/wasm32-emscripten/pic/libprintf_long_double-debug.a(vfprintf.o)
>>> defined in /emsdk/upstream/emscripten/cache/sysroot/lib/wasm32-emscripten/pic/libc-debug.a(vfprintf.o)
emcc: error: '/emsdk/upstream/bin/wasm-ld -o a.out.wasm --whole-archive /tmp/emscripten_temp_pbobb795/test_0.o -L/emsdk/upstream/emscripten/cache/sysroot/lib/wasm32-emscripten/pic -lGL-getprocaddr -lal -lhtml5 -lprintf_long_double-debug -lstubs-debug -lnoexit -lc-debug -ldlmalloc -lcompiler_rt -lc++-noexcept -lc++abi-debug-noexcept -lsockets --no-whole-archive -mllvm -combiner-global-alias-analysis=false -mllvm -enable-emscripten-sjlj -mllvm -disable-lsr --export-if-defined=setThrew --export-if-defined=_emscripten_stack_restore --export-if-defined=emscripten_stack_get_current --export-if-defined=_emscripten_tempret_set --export-if-defined=malloc --export-if-defined=_emscripten_stack_alloc --export-if-defined=_emscripten_tempret_get --export-if-defined=htons --export-if-defined=ntohs --export-if-defined=htonl --export-if-defined=_emscripten_timeout --export-if-defined=__cxa_is_pointer_type --export-if-defined=emscripten_stack_get_base --export-if-defined=emscripten_stack_get_end --export-if-defined=free --export-if-defined=__cxa_can_catch --export-if-defined=__cxa_increment_exception_refcount --export-if-defined=__cxa_decrement_exception_refcount --export-if-defined=fileno --export-if-defined=emscripten_builtin_memalign --export-if-defined=__dl_seterr --export-if-defined=memcmp --export-if-defined=memcpy --export-if-defined=__errno_location --export-if-defined=__cxa_demangle /tmp/tmpmzhuwxfwlibemscripten_js_symbols.so --import-memory --strip-debug --export-dynamic --export=emscripten_stack_get_end --export=emscripten_stack_get_free --export=emscripten_stack_get_base --export=emscripten_stack_get_current --export=emscripten_stack_set_limits --export=_emscripten_stack_alloc --export=__get_temp_ret --export=__set_temp_ret --export=__wasm_call_ctors --export=setThrew --export=_emscripten_stack_restore --export=_emscripten_tempret_set --export=malloc --export=_emscripten_tempret_get --export=htons --export=ntohs --export=htonl --export=_emscripten_timeout --export=__cxa_is_pointer_type --export=free --export=__cxa_can_catch --export=__cxa_increment_exception_refcount --export=__cxa_decrement_exception_refcount --export=fileno --export=emscripten_builtin_memalign --export=__dl_seterr --export=memcmp --export=memcpy --export=__errno_location --export=__cxa_demangle --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 --export-if-defined=__main_argc_argv --export-if-defined=__wasm_apply_data_relocs --export-if-defined=fflush --experimental-pic --unresolved-symbols=import-dynamic -pie -z stack-size=65536 --no-growable-memory --initial-memory=16777216 --no-entry --stack-first' failed (returned 1)

[sbc100]

Yes, this is an issue with -sMAIN_MODULE=1.

While we should fix this issue, I would also strongly recommend against using -sMAIN_MODULE=1 since it includes all symbols from all libraries and doesn't do any dead code elimination. If you can switch to -sMAIN_MODULE=2 that would solve this issue, and give you much smaller payloads.

[allsey87]

Indeed, however in this case I am compiling CPython and I think it is hard (impossible?) to know what functions will be needed by the imported modules.

[sbc100]

Are you working on pyodide? Or is this a separate CPython effort?

[allsey87]

A separate project that integrates CPython into a larger system

[sbc100]

If possible I would strongly advise against using -sMAIN_MODULE=2 and instead trying to come up with some sore of reasonable subset of symbols that your side modules have access to. I assume that dynamically loading side modules is hard requirement for you?

Fixing this particular issue is kind of pain due to the way that -sMAIN_MODULE wraps everything in -Wl,--whole-archive. I'll see if we can some up with reasonable fix though.

[allsey87]

So I don't need this issue fixed for my project, I am reporting it more because perhaps someone else can save themselves 5-10 minutes by just googling "emscripten __vfprintf_internal duplicate symbol" or something like that.