From mboxrd@z Thu Jan 1 00:00:00 1970 X-Spam-Checker-Version: SpamAssassin 3.4.4 (2020-01-24) on inbox.vuxu.org X-Spam-Level: X-Spam-Status: No, score=-1.0 required=5.0 tests=MAILING_LIST_MULTI, RCVD_IN_MSPIKE_H2 autolearn=ham autolearn_force=no version=3.4.4 Received: (qmail 17945 invoked from network); 7 Feb 2023 14:59:33 -0000 Received: from second.openwall.net (193.110.157.125) by inbox.vuxu.org with ESMTPUTF8; 7 Feb 2023 14:59:33 -0000 Received: (qmail 1139 invoked by uid 550); 7 Feb 2023 14:59:30 -0000 Mailing-List: contact musl-help@lists.openwall.com; run by ezmlm Precedence: bulk List-Post: List-Help: List-Unsubscribe: List-Subscribe: List-ID: Reply-To: musl@lists.openwall.com Received: (qmail 1092 invoked from network); 7 Feb 2023 14:59:29 -0000 Date: Tue, 7 Feb 2023 09:59:16 -0500 From: Rich Felker To: Peter Collingbourne Cc: Markus Wichmann , musl@lists.openwall.com Message-ID: <20230207145916.GQ4163@brightrain.aerifal.cx> References: <20230204063021.2681891-1-pcc@google.com> <20230205200003.GA1998@voyager> <20230205234930.GM4163@brightrain.aerifal.cx> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.5.21 (2010-09-15) Subject: Re: [musl] [PATCH] arm: Use __WCHAR_TYPE__ for wchar_t if defined On Mon, Feb 06, 2023 at 05:15:08PM -0800, Peter Collingbourne wrote: > On Sun, Feb 5, 2023 at 3:49 PM Rich Felker wrote: > > > > On Sun, Feb 05, 2023 at 09:00:03PM +0100, Markus Wichmann wrote: > > > On Sat, Feb 04, 2023 at 08:08:36AM +0100, alice wrote: > > > > On Sat Feb 4, 2023 at 7:30 AM CET, Peter Collingbourne wrote: > > > > > When building with -fshort-wchar the definition of wchar_t is > > > > > incorrect. Get the correct definition from the compiler if available. > > > > > > > > > > This is useful when reusing the freestanding parts of musl on a > > > > > bare-metal target that uses -fshort-wchar. > > > > > > > > somebody talked about this in 2015, see > > > > https://www.openwall.com/lists/musl/2015/02/18/2 > > > > for the previous discussion. > > > > > > > > i understand in this case it's proposed a little different- > > > > "reusing freestanding parts" as opposed to building a whole libc.so, but in > > > > that case you could most likely patch this in when reusing it standalone only? > > > > > > > > it doesn't seem a good idea for it to be there, in general. > > > > > > Seconded. A lot of code in musl depends on wchar_t being able to hold > > > the current maximum Unicode codepoint of 0x10FFFF at least, so the type > > > must be at least 21 bits. > > > > Absolutely. -fshort-wchar requests a different ABI that is > > fundamentally incompatible with libc and with use of the libc headers, > > and also fundamentally incompatible with Unicode and the requirements > > of the C language (unless you only want to support the BMP) -- C does > > not allow "multi-wchar_t characters". > > > > If you're targeting freestanding environment not using libc, you > > should use -nostdinc and provide headers suitable to your environment > > instead of the libc ones. But really you should fix the offending code > > not to use wchar_t for UTF-16, and not use -fshort-wchar. Modern C has > > a char16_t type for this purpose. > > Thanks, I agree with this and the other replies that I got. It did > seem at first that musl could be used unmodified in projects that > build with -fshort-wchar, but given the implications of a UTF-16 > wchar_t for the code that implements , it makes more sense > for this flag to be unsupported by musl and for any utilizing projects > to be fixed to not require -fshort-wchar. > > Currently we accidentally "support" -fshort-wchar on architectures > that happen to use __WCHAR_TYPE__ to define wchar_t. Would it make > sense to add something like a static assert to alltypes.h that checks > that sizeof(wchar_t) >= 4? If you count target-specific options, GCC probably has hundreds of options that produce incompatible/broken ABIs. We certainly don't have the means to trap all or even most of them. In the case of most, including -fshort-wchar, GCC documents this: "Warning: the -fshort-wchar switch causes GCC to generate code that is not binary compatible with code generated without that switch. Use it to conform to a non-default application binary interface." so I don't really think any action is needed. Rich