Weird clang "bug"

[latent goblet]

Call it a bug or not, the following behavior is quite surprising to me and I'm not sure to actually understand what's happening:

void exit(int code)
{
    extern void js_exit(int code);
    js_exit(code);
}


int accept(void)
{
    exit(-1);
}

when compiling this file, I get the following error:

clang --target=wasm32 \
                -std=c99 -nostdlib -Wextra -Wall -Werror -Wconversion -funsigned-char -pedantic-errors \
                -finput-charset=utf-8 -fexec-charset=utf-8 \
                -Os -flto \
                -Wl,--no-entry \
                -Wl,--allow-undefined-file=/home/src/js_symbols.syms \
                -Wl,--import-memory \
                -Wl,--export=__heap_base \
                -Wl,--export=accept \
                        /home/src/main.c \
                        /home/src/std/impl.c \
                -o /home/dist/app.wasm
/home/src/main.c:9:1: error: function declared 'noreturn' should not return [-Werror,-Winvalid-noreturn]
    9 | }
      | ^
1 error generated.

I suspect this is because of the special semantic of the exit function. if I rename the symbol to exot , it works fine (I get another compile error about accept not returning an int, which is fine)

where is the problem exactly? what is clang trying to do?

[midnight canopy]

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[gritty vapor]

does js_exit always return?

[latent goblet]

well, it is part of the symbols left undefned and injected at runtime. it is listed in the file linked here --allow-undefined-file=/home/src/js_symbols.syms

I have the same issue with _Exit

[latent goblet]

(in practice I think I could ask js_exit to throw an error. it would go against the contract of exit but maybe not the one of _Exit)

[gritty vapor]

try

__attribute__((noreturn)) extern void js_exit(int code);

or _Noreturn from C11

[latent goblet]

what does that do? I never tried __attribute__?

[gritty vapor]

GCC and Clang specific way of adding attributes

[latent goblet]

(yes it works now)

in the assumption I could inline some WASM directly to do this:

void _Exit(int code)
{
    __inline_wasm("unreachable");
}

I guess that "hack" wouldn't work, right?

(unreachable is a WASM instruction that makes the program stop)

[gritty vapor]

probably

though where is the code going to be shown

[latent goblet]

so essentially what happens is that, as the spec requires, _Exitshould never return. but in my case, it does return a data object of type void

which is not correct

is that so ?

void _Exit(int code)
{
    extern void js_exit(int code);
    js_exit(code);
    for(;;);
}

this works for example

[midnight canopy]

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[latent goblet]

do you think that alternatice is valid in C ? @gritty vapor , without compiler extension or anything ?

[gritty vapor]

yes

[latent goblet]

niiiiice

I love that lang

[gritty vapor]

might as well put the function in the for loop as well

[latent goblet]

indeed

[gritty vapor]

so it just repeatedly called until it quits

[latent goblet]

savage

but I like that

especially if on the JS side, I alert("Something went terribly wrong. close this tab asap")

because it blocks the thread

[gritty vapor]

lol

[latent goblet]

function js_exit(errorCode) {
  const message = `WASM module crashed hard. Error code: ${errorCode}`;
  alert(message, "\nClose this tab asap");
  throw message;
}

what a nice interop