Bug 2375150

This looks like an attempt in uboot-tools to use the termios2 kernel interfaces with the old glibc headers. Quoting the uboot-tools header:

/*
 * We need to use raw TCGETS2/TCSETS2 or TCGETS/TCSETS ioctls with the BOTHER
 * flag in struct termios2/termios, defined in Linux headers <asm/ioctls.h>
 * (included by <sys/ioctl.h>) and <asm/termbits.h>. Since these headers
 * conflict with glibc's header file <termios.h>, it is not possible to use
 * libc's termios functions and we need to reimplement them via ioctl() calls.
 *
 * An arbitrary baudrate is supported when the macro BOTHER is defined. The
 * baudrate value itself is then stored into the c_ospeed and c_ispeed members.
 * If ioctls TCGETS2/TCSETS2 are defined and supported then these fields are
 * present in struct termios2, otherwise these fields are present in struct
 * termios.
 *
 * Note that the Bnnn constants from <termios.h> need not be compatible with Bnnn
 * constants from <asm/termbits.h>.
 */

If the uboot-tools developers have suggestions how we can make the porting easier for them, maybe they can suggest that on libc-alpha?

I'll reach out to upstream

I've posted an RFC patch for u-boot: https://lists.denx.de/pipermail/u-boot/2025-June/593131.html

The problem as I understand it is that the PowerPC architecture does not define a struct termios2 as is the case for other architectures.

In https://elixir.bootlin.com/linux/v6.16-rc3/source/arch/powerpc/include/uapi/asm/termbits.h it says:

#define NCCS 19
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_cc[NCCS];		/* control characters */
	cc_t c_line;			/* line discipline (== c_cc[19]) */
	speed_t c_ispeed;		/* input speed */
	speed_t c_ospeed;		/* output speed */
};

/* For PowerPC the termios and ktermios are the same */

struct ktermios {
	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[NCCS];		/* control characters */
	cc_t c_line;			/* line discipline (== c_cc[19]) */
	speed_t c_ispeed;		/* input speed */
	speed_t c_ospeed;		/* output speed */
};

while all other architectures have a legacy struct termios and a struct termios2 that is the same than struct ktermios:

https://elixir.bootlin.com/linux/v6.16-rc3/source/include/uapi/asm-generic/termbits.h

#define NCCS 19
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 */
};

struct termios2 {
	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 */
};

struct ktermios {
	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 */
};

Given that the u-boot header that Florian mentioned, includes the kernel headers, then of course there's no struct termios2 for PowerPC.

Dan also mentioned this glibc https://sourceware.org/git/?p=glibc.git;a=commit;h=5f54d8bc48983bed844c02e1fe614ad223e78838

But AFAICT that change is not completely correct because is defining the TCGETS2/TCSETS*2 ioctls but using a struct termios2
that is not defined for PowerPC. Unless the #include <asm/ioctls.h> somehow includes the asm-generic headers that define the
struct termios2 ?

(In reply to Javier Martinez Canillas from comment #4)
> Dan also mentioned this glibc
> https://sourceware.org/git/?p=glibc.git;a=commit;
> h=5f54d8bc48983bed844c02e1fe614ad223e78838
> 
> But AFAICT that change is not completely correct because is defining the
> TCGETS2/TCSETS*2 ioctls but using a struct termios2
> that is not defined for PowerPC. Unless the #include <asm/ioctls.h> somehow
> includes the asm-generic headers that define the
> struct termios2 ?

None of this should be necessary with current glibc (at least I hope so) because it's now termios2-based on all architectures.  We could define _LIBC_LINUX_TERMIOS2 in <features.h> to help u-boot to help to disable the compatibility hacks.

(In reply to Florian Weimer from comment #5)
> (In reply to Javier Martinez Canillas from comment #4)
> > Dan also mentioned this glibc
> > https://sourceware.org/git/?p=glibc.git;a=commit;
> > h=5f54d8bc48983bed844c02e1fe614ad223e78838
> > 
> > But AFAICT that change is not completely correct because is defining the
> > TCGETS2/TCSETS*2 ioctls but using a struct termios2
> > that is not defined for PowerPC. Unless the #include <asm/ioctls.h> somehow
> > includes the asm-generic headers that define the
> > struct termios2 ?
> 
> None of this should be necessary with current glibc (at least I hope so)
> because it's now termios2-based on all architectures.  We could define
> _LIBC_LINUX_TERMIOS2 in <features.h> to help u-boot to help to disable the
> compatibility hacks.

I'm confused, but who defines the struct termios2 for the PowerPC architecture?

You said that current glibc it is now termios2-based on all architectures, but
I couldn't find where is defined for PowerPC.

Hmm. I missed the incorrect definition problem. I raised it on libc-alpha. Hopefully it's just a typo, and the constant should use struct termios.

(In reply to Florian Weimer from comment #7)
> Hmm. I missed the incorrect definition problem. I raised it on libc-alpha.
> Hopefully it's just a typo, and the constant should use struct termios.

Yes, that should work too.

for the record, https://sourceware.org/pipermail/libc-alpha/2025-July/168322.html

What is mentioned in https://sourceware.org/pipermail/libc-alpha/2025-July/168339.html is not accurate AFAICT:

"<linux/termios.h> defines it, but that header conflicts with <termios.h>."

but what I see in the Linux kernel source repo is the following:

$ make x86_64_defconfig prepare modules_prepare

$ cat ./arch/x86/include/generated/uapi/asm/termbits.h
#include <asm-generic/termbits.h>

$ grep "struct termios2" include/uapi/asm-generic/termbits.h 
19:struct termios2 {

$ head -n 40 arch/powerpc/include/uapi/asm/termbits.h
/* SPDX-License-Identifier: GPL-2.0+ WITH Linux-syscall-note */
#ifndef _ASM_POWERPC_TERMBITS_H
#define _ASM_POWERPC_TERMBITS_H

/*
 * This program is free software; you can redistribute it and/or
 * modify it under the terms of the GNU General Public License
 * as published by the Free Software Foundation; either version
 * 2 of the License, or (at your option) any later version.
 */

#include <asm-generic/termbits-common.h>

typedef unsigned int    tcflag_t;

/*
 * termios type and macro definitions.  Be careful about adding stuff
 * to this file since it's used in GNU libc and there are strict rules
 * concerning namespace pollution.
 */

#define NCCS 19
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_cc[NCCS];                /* control characters */
        cc_t c_line;                    /* line discipline (== c_cc[19]) */
        speed_t c_ispeed;               /* input speed */
        speed_t c_ospeed;               /* output speed */
};

/* For PowerPC the termios and ktermios are the same */

struct ktermios {
        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 */

In other words, struct termios and struct termios2 (if defined for the arch) are defined in <asm/termbits.h>,
which for x86 is just <asm-generic/termbits.h> and powerpc has its own that does not define a struct termios2.