From: David Laight <David.Laight@ACULAB.COM>
To: "'Maciej W. Rozycki'" <macro@orcam.me.uk>,
Paul Cercueil <paul@crapouillou.net>
Cc: "Jiri Slaby" <jslaby@suse.cz>,
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Subject: RE: [PATCH v3] serial: make uart_console_write->putchar()'s character an unsigned char
Date: Thu, 3 Mar 2022 11:44:42 +0000 [thread overview]
Message-ID: <9fa84690ed244eba89f1efe4e6670f80@AcuMS.aculab.com> (raw)
In-Reply-To: <alpine.DEB.2.21.2203031102570.50870@angie.orcam.me.uk>
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
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Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1PT, UK
Registration No: 1397386 (Wales)
next prev parent reply other threads:[~2022-03-03 11:44 UTC|newest]
Thread overview: 18+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-03-02 7:27 [PATCH v3] serial: make uart_console_write->putchar()'s character an unsigned char Jiri Slaby
2022-03-02 17:52 ` Uwe Kleine-König
2022-03-02 23:57 ` David Laight
2022-03-03 7:06 ` Jiri Slaby
2022-03-03 9:55 ` Maciej W. Rozycki
2022-03-03 10:22 ` Paul Cercueil
2022-03-03 11:30 ` Maciej W. Rozycki
2022-03-03 11:35 ` Jiri Slaby
2022-03-03 11:44 ` David Laight [this message]
2022-03-03 12:27 ` Paul Cercueil
2022-03-03 10:23 ` David Laight
2022-03-31 22:59 ` Maciej W. Rozycki
2022-03-02 18:21 ` Vladimir Zapolskiy
2022-03-03 6:32 ` Jiri Slaby
2022-03-03 7:45 ` Greg KH
2022-03-03 7:49 ` Jiri Slaby
2022-03-03 8:07 ` Greg KH
2022-03-03 8:09 ` Jiri Slaby
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