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Date: Sun, 1 Nov 2020 21:48:32 +0100
From: Wolf <wolf@wolfsden.cz>
To: musl@lists.openwall.com
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 <C6S7DCPAVDGM.3MUY7E2KQQCMO@mussels>
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Subject: Re: [musl] swprintf possible bug


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On 2020-11-01 17:17:49 -0300, =C3=89rico Nogueira wrote:
> For what it's worth, if this is a bug, it would seem to be in how musl
> decides when to print characters (not the formatting functions
> themselves), since the below program doesn't print anything:
>=20
> #include <wchar.h>
> #include <stdio.h>
>=20
> int main() {
>   fputws(L"[=D0=9F=D1=80=D0=B8=D0=B2=D0=B5=D1=82 =D0=92=D0=B0=D1=81=D0=B8=
=D0=BB=D0=B8=D0=B9]\n", stdout);
>   // I don't know if I'm accessing a wchar_t appropriately here
>   fputwc(L"[=D0=9F=D1=80=D0=B8=D0=B2=D0=B5=D1=82 =D0=92=D0=B0=D1=81=D0=B8=
=D0=BB=D0=B8=D0=B9]\n"[3], stdout);
>   return 0;
> }
>=20
> I tried tracing the execution from fputws, and not printing anything
> seems to be caused by the return value of wcsrtombs().

That seems to be on the right track, since when you actually check the
return code from fputws:

	#include <wchar.h>
	#include <stdio.h>

	int main(void) {
		if (fputws(L"[=D0=9F=D1=80=D0=B8=D0=B2=D0=B5=D1=82 =D0=92=D0=B0=D1=81=D0=
=B8=D0=BB=D0=B8=D0=B9]\n", stdout) =3D=3D -1) {
			perror("fputws");
		}
	}

you get this:

	# ./a
	fputws: Illegal byte sequence

I think it is caused by C (or POSIX) locale being default on entry to
main, so you need to actually activate the system locale by calling
setlocale(LC_ALL, "").

Indeed, if you modify the program to:

	#include <wchar.h>
	#include <stdio.h>
	#include <locale.h>

	int main(void) {
		setlocale(LC_ALL, "");
		if (fputws(L"[=D0=9F=D1=80=D0=B8=D0=B2=D0=B5=D1=82 =D0=92=D0=B0=D1=81=D0=
=B8=D0=BB=D0=B8=D0=B9]\n", stdout) =3D=3D -1) {
			perror("fputws");
		}
	}

It starts to work:

	# ./a
	[=D0=9F=D1=80=D0=B8=D0=B2=D0=B5=D1=82 =D0=92=D0=B0=D1=81=D0=B8=D0=BB=D0=B8=
=D0=B9]


W.

--=20
There are only two hard things in Computer Science:
cache invalidation, naming things and off-by-one errors.

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