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Date: Fri, 16 Nov 2012 08:27:08 +0000
From: Justin Cormack <>
Subject: Re: termios ugliness

On 16 Nov 2012 03:52, "Rich Felker" <> wrote:
> Hi all,
> In the process of integrating the powerpc port, it's come to my
> attention that the termios structure (used for setting terminal
> attributes) differs gratuitously between archs at the kernel level.
> glibc (and thus the LSB ABI, which we've tried to follow) fudges
> around this by always using the same userspace structure and
> translating from the kernelspace structure. I'm not sure what the
> benefit of this is (aside from having extra slots for expansion in
> c_cc array), but the downsides are (1) binary bloat and ugly
> arch-specific code for conversion, and (2) failure of a direct TCGETS
> ioctl (as opposed to a tcgetattr function call) to fill the struct
> properly, since it bypasses the translation.
> My leaning is to ignore the existing ABI on this and just use the
> arch-specific structure from the kernel on ppc and any other archs
> with this brokenness (alpha seems to be the main other one, possibly
> the only). Unlike x86, x86_64, or arm, I don't see a lot of usefulness
> in running glibc binaries on musl-powerpc; if it's ever needed, we
> could do patch-up work in the dynamic linker (which will eventually be
> needed anyway to deal with wrong regoff_t on x86_64 and 32-bit-off_t
> functions on 32-bit archs) to load such apps/libs.
> Since it's a decision we can't really change later without breaking
> ABI, though, I'd like to ask the community: does anybody have a strong
> feeling about whether we should use the kernel termios structure
> directly or do like glibc and use an arch-generic userspace termios
> structure and code to convert to/from the kernel version?
> The powerpc port will probably be considered experimental in the
> upcoming release, so we can take our time on the issue a bit, but I'd
> still rather hear comments sooner than later if you have some.
> Rich

I would prefer the kernel structure.


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