linux-kernel - RE: [PATCH v3] serial: make uart_console_write->putchar()'s character an unsigned char

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Date:   Thu, 3 Mar 2022 11:44:42 +0000
From:   David Laight <David.Laight@...LAB.COM>
To:     "'Maciej W. Rozycki'" <macro@...am.me.uk>,
        Paul Cercueil <paul@...pouillou.net>
CC:     Jiri Slaby <jslaby@...e.cz>,
        'Uwe Kleine-König' 
        <u.kleine-koenig@...gutronix.de>,
        "gregkh@...uxfoundation.org" <gregkh@...uxfoundation.org>,
        Alexandre Belloni <alexandre.belloni@...tlin.com>,
        Mateusz Holenko <mholenko@...micro.com>,
        Neil Armstrong <narmstrong@...libre.com>,
        Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Liviu Dudau <liviu.dudau@....com>,
        Baruch Siach <baruch@...s.co.il>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Paul Mackerras <paulus@...ba.org>,
        "Michael Ellerman" <mpe@...erman.id.au>,
        Michal Simek <michal.simek@...inx.com>,
        "Karol Gugala" <kgugala@...micro.com>,
        Jerome Brunet <jbrunet@...libre.com>,
        "Peter Korsgaard" <peter@...sgaard.com>,
        Florian Fainelli <f.fainelli@...il.com>,
        Alexander Shiyan <shc_work@...l.ru>,
        Krzysztof Kozlowski <krzysztof.kozlowski@...onical.com>,
        Alexandre Torgue <alexandre.torgue@...s.st.com>,
        Fabio Estevam <festevam@...il.com>,
        "Russell King" <linux@...linux.org.uk>,
        Ludovic Desroches <ludovic.desroches@...rochip.com>,
        Andy Gross <agross@...nel.org>,
        "bcm-kernel-feedback-list@...adcom.com" 
        <bcm-kernel-feedback-list@...adcom.com>,
        NXP Linux Team <linux-imx@....com>,
        "linux-serial@...r.kernel.org" <linux-serial@...r.kernel.org>,
        Vineet Gupta <vgupta@...nel.org>,
        Orson Zhai <orsonzhai@...il.com>,
        Tobias Klauser <tklauser@...tanz.ch>,
        Patrice Chotard <patrice.chotard@...s.st.com>,
        "Albert Ou" <aou@...s.berkeley.edu>,
        Maxime Coquelin <mcoquelin.stm32@...il.com>,
        Manivannan Sadhasivam <mani@...nel.org>,
        Martin Blumenstingl <martin.blumenstingl@...glemail.com>,
        Sascha Hauer <s.hauer@...gutronix.de>,
        Takao Orito <orito.takao@...ionext.com>,
        Vladimir Zapolskiy <vz@...ia.com>,
        Lorenzo Pieralisi <lorenzo.pieralisi@....com>,
        Paul Walmsley <paul.walmsley@...ive.com>,
        Bjorn Andersson <bjorn.andersson@...aro.org>,
        Sudeep Holla <sudeep.holla@....com>,
        Richard Genoud <richard.genoud@...il.com>,
        Chunyan Zhang <zhang.lyra@...il.com>,
        "Nicolas Ferre" <nicolas.ferre@...rochip.com>,
        "David S. Miller" <davem@...emloft.net>,
        Taichi Sugaya <sugaya.taichi@...ionext.com>,
        Palmer Dabbelt <palmer@...belt.com>,
        Pengutronix Kernel Team <kernel@...gutronix.de>,
        "Kevin Hilman" <khilman@...libre.com>,
        Baolin Wang <baolin.wang7@...il.com>,
        "Shawn Guo" <shawnguo@...nel.org>,
        Andreas Färber <afaerber@...e.de>
Subject: RE: [PATCH v3] serial: make uart_console_write->putchar()'s character
 an unsigned char

From: Maciej W. Rozycki
> Sent: 03 March 2022 11:31
..
>  It does, but, oh dear, it's a "solution" to a problem we have created in
> the first place.  Why do we ever want to have signed characters in the TTY
> layer, and then to vary between platforms?  It's asking for portability
> issues.

C 'char' is signed because the pdp/11 byte load sign extended.

I guess some ABI use unsigned char to avoid issues with all
the functions that take/return an int parameter that is
either a 'char' cast to 'unsigned char' or EOF.

EOF is usually (-1) - but doesn't have to be.
But it needs to be different from any value obtained
by casting a 'char' to 'unsigned char'.
(But that may only need to be all characters, not all values of 'char'.)

Then you get the requirement that:
	sizeof (int) >= sizeof (short) >= sizeof (char)
which means that it is perfectly valid for all 3 to be the same size [1].
In that case 'unsigned char' promotes to 'unsigned int'
which probably breaks some code.
It also makes defining EOF troublesome!

[1] The C compiler for a DSP had this 'feature'.

	David

-
Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1PT, UK
Registration No: 1397386 (Wales)