Hi!
While compiling an example program in ioctl_tty(2) examples (now moving
to TCSETS(2const)), I saw several warnings:
tcgets.c:53:24: error: implicit conversion changes signedness: 'int' to 'tcflag_t' (aka 'unsigned int') [clang-diagnostic-sign-conversion,-warnings-as-errors]
tio.c_cflag &= ~CBAUD;
~~ ^~~~~~
tcgets.c:53:24: warning: use of a signed integer operand with a binary bitwise operator [hicpp-signed-bitwise]
tio.c_cflag &= ~CBAUD;
~~ ^~~~~~
tcgets.c:58:24: error: implicit conversion changes signedness: 'int' to 'tcflag_t' (aka 'unsigned int') [clang-diagnostic-sign-conversion,-warnings-as-errors]
tio.c_cflag &= ~(CBAUD << IBSHIFT);
~~ ^~~~~~~~~~~~~~~~~~~
tcgets.c:58:24: warning: use of a signed integer operand with a binary bitwise operator [hicpp-signed-bitwise]
tio.c_cflag &= ~(CBAUD << IBSHIFT);
~~ ^~~~~~~~~~~~~~~~~~~
tcgets.c:58:25: warning: use of a signed integer operand with a unary bitwise operator [hicpp-signed-bitwise]
tio.c_cflag &= ~(CBAUD << IBSHIFT);
~^~~~~~~~~~~~~~~~~~
Which seem reasonable warnings. Bitwise operations on signed integers
is bad for ye health. Let's see the definitions of struct termios:
alx@debian:/usr/include$ grepc termios x86_64-linux-gnu/ asm-generic/
x86_64-linux-gnu/bits/termios-struct.h:struct termios
{
tcflag_t c_iflag; /* input mode flags */
tcflag_t c_oflag; /* output mode flags */
tcflag_t c_cflag; /* control mode flags */
tcflag_t c_lflag; /* local mode flags */
cc_t c_line; /* line discipline */
cc_t c_cc[NCCS]; /* control characters */
speed_t c_ispeed; /* input speed */
speed_t c_ospeed; /* output speed */
#define _HAVE_STRUCT_TERMIOS_C_ISPEED 1
#define _HAVE_STRUCT_TERMIOS_C_OSPEED 1
};
asm-generic/termbits.h:struct termios {
tcflag_t c_iflag; /* input mode flags */
tcflag_t c_oflag; /* output mode flags */
tcflag_t c_cflag; /* control mode flags */
tcflag_t c_lflag; /* local mode flags */
cc_t c_line; /* line discipline */
cc_t c_cc[NCCS]; /* control characters */
};
Except for the speed members, they seem the same. The types of the
members are correctly unsigned:
alx@debian:/usr/include$ grepc tcflag_t x86_64-linux-gnu/ asm-generic/
x86_64-linux-gnu/bits/termios.h:typedef unsigned int tcflag_t;
asm-generic/termbits.h:typedef unsigned int tcflag_t;
So, all of the constants that are to be used in these members, which
will undergo bitwise operations, should use the U suffix. Here's the
list for the UAPI:
$ sed -n '/flag bits/,/^$/p' asm-generic/termbits.h
/* c_iflag bits */
#define IUCLC 0x0200
#define IXON 0x0400
#define IXOFF 0x1000
#define IMAXBEL 0x2000
#define IUTF8 0x4000
/* c_oflag bits */
#define OLCUC 0x00002
#define ONLCR 0x00004
#define NLDLY 0x00100
#define NL0 0x00000
#define NL1 0x00100
#define CRDLY 0x00600
#define CR0 0x00000
#define CR1 0x00200
#define CR2 0x00400
#define CR3 0x00600
#define TABDLY 0x01800
#define TAB0 0x00000
#define TAB1 0x00800
#define TAB2 0x01000
#define TAB3 0x01800
#define XTABS 0x01800
#define BSDLY 0x02000
#define BS0 0x00000
#define BS1 0x02000
#define VTDLY 0x04000
#define VT0 0x00000
#define VT1 0x04000
#define FFDLY 0x08000
#define FF0 0x00000
#define FF1 0x08000
/* c_lflag bits */
#define ISIG 0x00001
#define ICANON 0x00002
#define XCASE 0x00004
#define ECHO 0x00008
#define ECHOE 0x00010
#define ECHOK 0x00020
#define ECHONL 0x00040
#define NOFLSH 0x00080
#define TOSTOP 0x00100
#define ECHOCTL 0x00200
#define ECHOPRT 0x00400
#define ECHOKE 0x00800
#define FLUSHO 0x01000
#define PENDIN 0x04000
#define IEXTEN 0x08000
#define EXTPROC 0x10000
And glibc also (re)defines some of them, so those should also have the
U suffix.
Any opinions?
Have a lovely day!
Alex
--
<https://www.alejandro-colomar.es/>
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