linux: implement arbitrary and split speeds in termios

Linux has supported arbitrary speeds and split speeds in the kernel
since 2008 on all platforms except Alpha (fixed in 2020), but glibc
was never updated to match. This is further complicated by POSIX uses
of macros for the cf[gs]et[io]speed interfaces, rather than plain
numbers, as it really ought to have.

On most platforms, the glibc ABI includes the c_[io]speed fields in
struct termios, but they are incorrectly used. On MIPS and SPARC, they
are entirely missing.

For backwards compatibility, the kernel will still use the legacy
speed fields unless they are set to BOTHER, and will use the legacy
output speed as the input speed if the latter is 0 (== B0). However,
the specific encoding used is visible to user space applications,
including ones other than the one running.

- SPARC and MIPS get a new struct termios, and tc[gs]etattr() is
  versioned accordingly. However, the new struct termios is set to be
  a strict extension of the old one, which means that cf* interfaces
  other than the speed-related ones do not need versioning.
- The Bxxx constants are redefined as equivalent to their integer
  values and the legacy Bxxx constants are renamed __Bxxx.
- cf[gs]et[io]speed() and cfsetspeed() are versioned accordingly.
- tcgetattr() and cfset[io]speed() are adjusted to always keep the
  c_[io]speed fields correct (unlike earlier versions), but to
  canonicalize the representation to ALSO configure the legacy fields
  if a valid legacy representation exists.
- tcsetattr(), too, canonicalizes the representation in this way
  before passing it to the kernel, to maximize compatibility with
  older applications/tools.
- The old IBAUD0 hack is removed; it is no longer necessary since
  even the legacy c_cflag baud rate fields have had separate input
  values for a long time.

Signed-off-by: H. Peter Anvin (Intel) <hpa@zytor.com>
Reviewed-by: Adhemerval Zanella  <adhemerval.zanella@linaro.org>

6 files changed, 65 insertions, 65 deletions

diff --git a/sysdeps/unix/sysv/linux/alpha/bits/termios-c_cflag.h b/sysdeps/unix/sysv/linux/alpha/bits/termios-c_cflag.h
index 1f9f7f2..d830884 100644
--- a/sysdeps/unix/sysv/linux/alpha/bits/termios-c_cflag.h
+++ b/sysdeps/unix/sysv/linux/alpha/bits/termios-c_cflag.h
@@ -36,4 +36,6 @@
 
 #ifdef __USE_MISC
 # define ADDRB 04000000000
+# define CMSPAR  010000000000 /* Mark or space (stick) parity.  */
+# define CRTSCTS 020000000000 /* Flow control.  */
 #endif
diff --git a/sysdeps/unix/sysv/linux/alpha/bits/termios-baud.h b/sysdeps/unix/sysv/linux/alpha/bits/termios-cbaud.h
index 324d5d8..69421f6 100644
--- a/sysdeps/unix/sysv/linux/alpha/bits/termios-baud.h
+++ b/sysdeps/unix/sysv/linux/alpha/bits/termios-cbaud.h
@@ -17,30 +17,29 @@
    <https://www.gnu.org/licenses/>.  */
 
 #ifndef _TERMIOS_H
-# error "Never include <bits/termios-baud.h> directly; use <termios.h> instead."
+# error "Never include <bits/termios-cbaud.h> directly; use <termios.h> instead."
 #endif
 
 #ifdef __USE_MISC
-# define CBAUD	0000037
-# define CBAUDEX 0000000
-# define CMSPAR	  010000000000		/* mark or space (stick) parity */
-# define CRTSCTS  020000000000		/* flow control */
+# define CBAUD	    000000037
+# define CBAUDEX    000000000
+# define CIBAUD     007600000
+# define IBSHIFT    16
 #endif
 
-#define  B57600   00020
-#define  B115200  00021
-#define  B230400  00022
-#define  B460800  00023
-#define  B500000  00024
-#define  B576000  00025
-#define  B921600  00026
-#define  B1000000 00027
-#define  B1152000 00030
-#define  B1500000 00031
-#define  B2000000 00032
-#define  B2500000 00033
-#define  B3000000 00034
-#define  B3500000 00035
-#define  B4000000 00036
-
-#define __MAX_BAUD B4000000
+#define  __B57600   00020
+#define  __B115200  00021
+#define  __B230400  00022
+#define  __B460800  00023
+#define  __B500000  00024
+#define  __B576000  00025
+#define  __B921600  00026
+#define  __B1000000 00027
+#define  __B1152000 00030
+#define  __B1500000 00031
+#define  __B2000000 00032
+#define  __B2500000 00033
+#define  __B3000000 00034
+#define  __B3500000 00035
+#define  __B4000000 00036
+#define  __BOTHER   00037
diff --git a/sysdeps/unix/sysv/linux/alpha/kernel-features.h b/sysdeps/unix/sysv/linux/alpha/kernel-features.h
index 6eae48f..83fdf91 100644
--- a/sysdeps/unix/sysv/linux/alpha/kernel-features.h
+++ b/sysdeps/unix/sysv/linux/alpha/kernel-features.h
@@ -54,4 +54,15 @@
 #undef __ASSUME_CLONE3
 #define __ASSUME_CLONE3 0
 
+/* Alpha did not provide BOTHER, CIBAUD or the termios2 ioctls until
+   kernel 4.20.  Even though struct __kernel_termios and struct
+   termios2 are the same on Alpha, Calling the legacy TCSETS* ioctls
+   with BOTHER set triggers a bug in these old kernels, so only use
+   the legacy TCSETS* ioctl numbers if neither BOTHER nor split speed is
+   needed; that way the code will fail gracefully. */
+#if __LINUX_KERNEL_VERSION < 0x041400
+# undef  __ASSUME_TERMIOS2
+# define __ASSUME_TERMIOS2 0
+#endif
+
 #endif /* _KERNEL_FEATURES_H */
diff --git a/sysdeps/unix/sysv/linux/alpha/kernel_termios.h b/sysdeps/unix/sysv/linux/alpha/kernel_termios.h
deleted file mode 100644
index 6a777dd..0000000
--- a/sysdeps/unix/sysv/linux/alpha/kernel_termios.h
+++ /dev/null
@@ -1,43 +0,0 @@
-/* Copyright (C) 1997-2025 Free Software Foundation, Inc.
-   This file is part of the GNU C Library.
-
-   The GNU C Library is free software; you can redistribute it and/or
-   modify it under the terms of the GNU Lesser General Public
-   License as published by the Free Software Foundation; either
-   version 2.1 of the License, or (at your option) any later version.
-
-   The GNU C Library is distributed in the hope that it will be useful,
-   but WITHOUT ANY WARRANTY; without even the implied warranty of
-   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
-   Lesser General Public License for more details.
-
-   You should have received a copy of the GNU Lesser General Public
-   License along with the GNU C Library.  If not, see
-   <https://www.gnu.org/licenses/>.  */
-
-#ifndef _KERNEL_TERMIOS_H
-#define _KERNEL_TERMIOS_H 1
-
-/* The following corresponds to the values from the Linux 2.1.20 kernel.  */
-
-/* We need the definition of tcflag_t, cc_t, and speed_t.  */
-#include <termios.h>
-
-#define __KERNEL_NCCS 19
-
-struct __kernel_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_cc[__KERNEL_NCCS];	/* control characters */
-    cc_t c_line;		/* line discipline */
-    speed_t c_ispeed;		/* input speed */
-    speed_t c_ospeed;		/* output speed */
-  };
-
-#define _HAVE_C_ISPEED 1
-#define _HAVE_C_OSPEED 1
-
-#endif /* kernel_termios.h */
diff --git a/sysdeps/unix/sysv/linux/alpha/libc.abilist b/sysdeps/unix/sysv/linux/alpha/libc.abilist
index d5df965..1e3f278 100644
--- a/sysdeps/unix/sysv/linux/alpha/libc.abilist
+++ b/sysdeps/unix/sysv/linux/alpha/libc.abilist
@@ -3099,6 +3099,11 @@ GLIBC_2.41 sched_getattr F
 GLIBC_2.41 sched_setattr F
 GLIBC_2.42 __inet_ntop_chk F
 GLIBC_2.42 __inet_pton_chk F
+GLIBC_2.42 cfgetispeed F
+GLIBC_2.42 cfgetospeed F
+GLIBC_2.42 cfsetispeed F
+GLIBC_2.42 cfsetospeed F
+GLIBC_2.42 cfsetspeed F
 GLIBC_2.42 pthread_gettid_np F
 GLIBC_2.42 uabs F
 GLIBC_2.42 uimaxabs F
diff --git a/sysdeps/unix/sysv/linux/alpha/termios_arch.h b/sysdeps/unix/sysv/linux/alpha/termios_arch.h
new file mode 100644
index 0000000..20025f2
--- /dev/null
+++ b/sysdeps/unix/sysv/linux/alpha/termios_arch.h
@@ -0,0 +1,26 @@
+/* Architectural parameters for Linux termios - Alpha/PowerPC version
+
+   Copyright (C) 1997-2025 Free Software Foundation, Inc.
+   This file is part of the GNU C Library.
+
+   The GNU C Library is free software; you can redistribute it and/or
+   modify it under the terms of the GNU Lesser General Public
+   License as published by the Free Software Foundation; either
+   version 2.1 of the License, or (at your option) any later version.
+
+   The GNU C Library is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+   Lesser General Public License for more details.
+
+   You should have received a copy of the GNU Lesser General Public
+   License along with the GNU C Library; if not, see
+   <https://www.gnu.org/licenses/>.  */
+
+#ifndef TERMIOS_INTERNALS_H
+# error "<termios_arch.h> should only be included from <termios_internals.h>"
+#endif
+
+#define _TERMIOS2_NCCS 19
+#define _HAVE_TERMIOS2_C_CC_BEFORE_C_LINE 1
+#define _HAVE_STRUCT_OLD_TERMIOS 0