Fails to compile when using strdup C23 standard function

[BlackGoku36]

Please include the following in your bug report:

Version of emscripten/emsdk:
emcc (Emscripten gcc/clang-like replacement + linker emulating GNU ld) 3.1.74 (1092ec3)
clang version 20.0.0git (https:/github.com/llvm/llvm-project 322eb1a92e6d4266184060346616fa0dbe39e731)
Target: wasm32-unknown-emscripten
Thread model: posix
InstalledDir: /Users/x/emsdk/upstream/bin

Failing command line in full:
Command line:

-> emcc src/usdc.c src/token.c external/lz4/lib/lz4.c -I external/lz4/lib -std=c23 -o build/wasm/wasm_usdc.html -Wall -Wextra --preload-file data -sMEMORY64=2

Output:

src/token.c:169:10: error: use of undeclared identifier 'strdup'; did you mean 'strupr'?
  169 |                 .str = strdup(str),
      |                        ^~~~~~
      |                        strupr
/Users/urjasvisuthar/emsdk/upstream/emscripten/cache/sysroot/include/compat/string.h:9:14: note: 'strupr' declared here
    9 | extern char* strupr(char *);
      |              ^
1 error generated.
emcc: error: '/Users/urjasvisuthar/emsdk/upstream/bin/clang -target wasm64-unknown-emscripten -fignore-exceptions -mno-bulk-memory -mno-bulk-memory-opt -mno-nontrapping-fptoint -mllvm -combiner-global-alias-analysis=false -mllvm -enable-emscripten-sjlj -mllvm -disable-lsr --sysroot=/Users/urjasvisuthar/emsdk/upstream/emscripten/cache/sysroot -DEMSCRIPTEN -Werror=implicit-function-declaration -Xclang -iwithsysroot/include/fakesdl -Xclang -iwithsysroot/include/compat -Iexternal/lz4/lib -std=c23 -Wall -Wextra src/token.c -c -o /var/folders/7x/khcwdw3d39g8c3k03mcrcw3r0000gn/T/emscripten_temp_5hhhrejl/token_1.o' failed (returned 1)

---

Full link command and output with -v appended:
Command line:

emcc src/usdc.c src/token.c external/lz4/lib/lz4.c -I external/lz4/lib -std=c23 -o build/wasm/wasm_usdc.html -Wall -Wextra --preload-file data -sMEMORY64=2 -v

Output:

/Users/urjasvisuthar/emsdk/upstream/bin/clang -target wasm64-unknown-emscripten -fignore-exceptions -mno-bulk-memory -mno-bulk-memory-opt -mno-nontrapping-fptoint -mllvm -combiner-global-alias-analysis=false -mllvm -enable-emscripten-sjlj -mllvm -disable-lsr --sysroot=/Users/urjasvisuthar/emsdk/upstream/emscripten/cache/sysroot -DEMSCRIPTEN -Werror=implicit-function-declaration -Xclang -iwithsysroot/include/fakesdl -Xclang -iwithsysroot/include/compat -Iexternal/lz4/lib -std=c23 -Wall -Wextra -v src/usdc.c -c -o /var/folders/7x/khcwdw3d39g8c3k03mcrcw3r0000gn/T/emscripten_temp_s3__nidp/usdc_0.o
clang version 20.0.0git (https:/github.com/llvm/llvm-project 322eb1a92e6d4266184060346616fa0dbe39e731)
Target: wasm64-unknown-emscripten
Thread model: posix
InstalledDir: /Users/urjasvisuthar/emsdk/upstream/bin
 (in-process)
 "/Users/urjasvisuthar/emsdk/upstream/bin/clang-20" -cc1 -triple wasm64-unknown-emscripten -emit-obj -disable-free -clear-ast-before-backend -disable-llvm-verifier -discard-value-names -main-file-name usdc.c -mrelocation-model static -mframe-pointer=none -ffp-contract=on -fno-rounding-math -mconstructor-aliases -target-cpu generic -target-feature -bulk-memory -target-feature -bulk-memory-opt -target-feature -nontrapping-fptoint -fvisibility=hidden -debugger-tuning=gdb -fdebug-compilation-dir=/Users/urjasvisuthar/Desktop/test/fta -v -fcoverage-compilation-dir=/Users/urjasvisuthar/Desktop/test/fta -resource-dir /Users/urjasvisuthar/emsdk/upstream/lib/clang/20 -D EMSCRIPTEN -I external/lz4/lib -isysroot /Users/urjasvisuthar/emsdk/upstream/emscripten/cache/sysroot -internal-isystem /Users/urjasvisuthar/emsdk/upstream/lib/clang/20/include -internal-isystem /Users/urjasvisuthar/emsdk/upstream/emscripten/cache/sysroot/include/wasm64-emscripten -internal-isystem /Users/urjasvisuthar/emsdk/upstream/emscripten/cache/sysroot/include -Werror=implicit-function-declaration -Wall -Wextra -std=c23 -ferror-limit 19 -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 /var/folders/7x/khcwdw3d39g8c3k03mcrcw3r0000gn/T/emscripten_temp_s3__nidp/usdc_0.o -x c src/usdc.c
clang -cc1 version 20.0.0git based upon LLVM 20.0.0git default target x86_64-apple-darwin24.1.0
ignoring nonexistent directory "/Users/urjasvisuthar/emsdk/upstream/emscripten/cache/sysroot/include/wasm64-emscripten"
#include "..." search starts here:
#include <...> search starts here:
 external/lz4/lib
 /Users/urjasvisuthar/emsdk/upstream/emscripten/cache/sysroot/include/fakesdl
 /Users/urjasvisuthar/emsdk/upstream/emscripten/cache/sysroot/include/compat
 /Users/urjasvisuthar/emsdk/upstream/lib/clang/20/include
 /Users/urjasvisuthar/emsdk/upstream/emscripten/cache/sysroot/include
End of search list.
 /Users/urjasvisuthar/emsdk/upstream/bin/clang -target wasm64-unknown-emscripten -fignore-exceptions -mno-bulk-memory -mno-bulk-memory-opt -mno-nontrapping-fptoint -mllvm -combiner-global-alias-analysis=false -mllvm -enable-emscripten-sjlj -mllvm -disable-lsr --sysroot=/Users/urjasvisuthar/emsdk/upstream/emscripten/cache/sysroot -DEMSCRIPTEN -Werror=implicit-function-declaration -Xclang -iwithsysroot/include/fakesdl -Xclang -iwithsysroot/include/compat -Iexternal/lz4/lib -std=c23 -Wall -Wextra -v src/token.c -c -o /var/folders/7x/khcwdw3d39g8c3k03mcrcw3r0000gn/T/emscripten_temp_s3__nidp/token_1.o
clang version 20.0.0git (https:/github.com/llvm/llvm-project 322eb1a92e6d4266184060346616fa0dbe39e731)
Target: wasm64-unknown-emscripten
Thread model: posix
InstalledDir: /Users/urjasvisuthar/emsdk/upstream/bin
 (in-process)
 "/Users/urjasvisuthar/emsdk/upstream/bin/clang-20" -cc1 -triple wasm64-unknown-emscripten -emit-obj -disable-free -clear-ast-before-backend -disable-llvm-verifier -discard-value-names -main-file-name token.c -mrelocation-model static -mframe-pointer=none -ffp-contract=on -fno-rounding-math -mconstructor-aliases -target-cpu generic -target-feature -bulk-memory -target-feature -bulk-memory-opt -target-feature -nontrapping-fptoint -fvisibility=hidden -debugger-tuning=gdb -fdebug-compilation-dir=/Users/urjasvisuthar/Desktop/test/fta -v -fcoverage-compilation-dir=/Users/urjasvisuthar/Desktop/test/fta -resource-dir /Users/urjasvisuthar/emsdk/upstream/lib/clang/20 -D EMSCRIPTEN -I external/lz4/lib -isysroot /Users/urjasvisuthar/emsdk/upstream/emscripten/cache/sysroot -internal-isystem /Users/urjasvisuthar/emsdk/upstream/lib/clang/20/include -internal-isystem /Users/urjasvisuthar/emsdk/upstream/emscripten/cache/sysroot/include/wasm64-emscripten -internal-isystem /Users/urjasvisuthar/emsdk/upstream/emscripten/cache/sysroot/include -Werror=implicit-function-declaration -Wall -Wextra -std=c23 -ferror-limit 19 -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 /var/folders/7x/khcwdw3d39g8c3k03mcrcw3r0000gn/T/emscripten_temp_s3__nidp/token_1.o -x c src/token.c
clang -cc1 version 20.0.0git based upon LLVM 20.0.0git default target x86_64-apple-darwin24.1.0
ignoring nonexistent directory "/Users/urjasvisuthar/emsdk/upstream/emscripten/cache/sysroot/include/wasm64-emscripten"
#include "..." search starts here:
#include <...> search starts here:
 external/lz4/lib
 /Users/urjasvisuthar/emsdk/upstream/emscripten/cache/sysroot/include/fakesdl
 /Users/urjasvisuthar/emsdk/upstream/emscripten/cache/sysroot/include/compat
 /Users/urjasvisuthar/emsdk/upstream/lib/clang/20/include
 /Users/urjasvisuthar/emsdk/upstream/emscripten/cache/sysroot/include
End of search list.
src/token.c:169:10: error: use of undeclared identifier 'strdup'; did you mean 'strupr'?
  169 |                 .str = strdup(str),
      |                        ^~~~~~
      |                        strupr
/Users/urjasvisuthar/emsdk/upstream/emscripten/cache/sysroot/include/compat/string.h:9:14: note: 'strupr' declared here
    9 | extern char* strupr(char *);
      |              ^
1 error generated.
emcc: error: '/Users/urjasvisuthar/emsdk/upstream/bin/clang -target wasm64-unknown-emscripten -fignore-exceptions -mno-bulk-memory -mno-bulk-memory-opt -mno-nontrapping-fptoint -mllvm -combiner-global-alias-analysis=false -mllvm -enable-emscripten-sjlj -mllvm -disable-lsr --sysroot=/Users/urjasvisuthar/emsdk/upstream/emscripten/cache/sysroot -DEMSCRIPTEN -Werror=implicit-function-declaration -Xclang -iwithsysroot/include/fakesdl -Xclang -iwithsysroot/include/compat -Iexternal/lz4/lib -std=c23 -Wall -Wextra -v src/token.c -c -o /var/folders/7x/khcwdw3d39g8c3k03mcrcw3r0000gn/T/emscripten_temp_s3__nidp/token_1.o' failed (returned 1)

---

Google group conversation:
https://groups.google.com/g/emscripten-discuss/c/3DMpT62eLuE

[drmdanowar]

This is the most important part of the best way

[sbc100]

The reason for this is that -std=c23 (or -std=c11) will define __STRICT_ANSI__ and musl assumes that this means that strdup is not available:

emscripten/system/lib/libc/musl/include/string.h

Lines 62 to 77 in 1ce7ff5

	#if defined(_POSIX_SOURCE) || defined(_POSIX_C_SOURCE) \
	|| defined(_XOPEN_SOURCE) || defined(_GNU_SOURCE) \
	|| defined(_BSD_SOURCE)
	char *strtok_r (char *__restrict, const char *__restrict, char **__restrict);
	int strerror_r (int, char *, size_t);
	char *stpcpy(char *__restrict, const char *__restrict);
	char *stpncpy(char *__restrict, const char *__restrict, size_t);
	size_t strnlen (const char *, size_t);
	char *strdup (const char *);
	char *strndup (const char *, size_t);
	char *strsignal(int);
	char *strerror_l (int, locale_t);
	int strcoll_l (const char *, const char *, locale_t);
	size_t strxfrm_l (char *__restrict, const char *__restrict, size_t, locale_t);
	void *memmem(const void *, size_t, const void *, size_t);
	#endif

While this assumption was try for c11 it is no longer true for c23 which added strdup to the standard: https://en.cppreference.com/w/c/string/byte/strdup

Kind of crazy that strdup was not part of the C standard until 2023 :)

Anyway, I think musl upstream is looking into fixing this: https://www.openwall.com/lists/musl/2023/05/31/20.

We could fix it downstream ahead of them if folks are running into this.