linux-kernel - Re: [PATCH] x86/asm/entry/32: Rename labels in INT 0x80 code path

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Date:	Mon, 8 Jun 2015 12:17:12 -0700
From:	Andy Lutomirski <luto@...capital.net>
To:	Ingo Molnar <mingo@...nel.org>
Cc:	Brian Gerst <brgerst@...il.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Denys Vlasenko <dvlasenk@...hat.com>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Kees Cook <keescook@...omium.org>,
	Borislav Petkov <bp@...en8.de>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Alexei Starovoitov <ast@...mgrid.com>,
	Oleg Nesterov <oleg@...hat.com>,
	Will Drewry <wad@...omium.org>,
	Steven Rostedt <rostedt@...dmis.org>,
	"the arch/x86 maintainers" <x86@...nel.org>,
	"H. Peter Anvin" <hpa@...or.com>
Subject: Re: [PATCH] x86/asm/entry/32: Rename labels in INT 0x80 code path

On Mon, Jun 8, 2015 at 12:14 PM, Ingo Molnar <mingo@...nel.org> wrote:
>
> * Brian Gerst <brgerst@...il.com> wrote:
>
>> On Mon, Jun 8, 2015 at 1:35 AM, Ingo Molnar <mingo@...nel.org> wrote:
>> >
>> > * Linus Torvalds <torvalds@...ux-foundation.org> wrote:
>> >
>> >> On Jun 7, 2015 11:42 AM, "Denys Vlasenko" <dvlasenk@...hat.com> wrote:
>> >> >
>> >> > Rename it to ia32_int80_target.
>> >>
>> >> Btw, could we arrive to get rid of the idiotic "ia32" naming too? It's wrong,
>> >> and it harkens back to the days when intel thought itanium makes sense and
>> >> wanted to talk about "intel architecture".
>> >
>> > Absolutely, I've been slowly eliminating uses of it - that naming is very
>> > annoying.
>> >
>> > Another thing I'm doing is to slowly remove references to 'emulation' - we
>> > don't emulate 32-bit in any way, we implement various 32-bit syscall ABIs (old
>> > a new) natively.
>> >
>> > I'd like to remove CONFIG_IA32_EMULATION from the .config as well - it offers
>> > nothing real over CONFIG_COMPAT.
>>
>> A few months ago I started working on a set of patches to decouple the X32
>> support from the 32-bit compat support.  There is actually quite a bit of
>> non-shared code between the two, mainly signal handling and syscall entries.
>> The code used by both should be CONFIG_COMPAT, but separate config defines
>> should be kept for the non-shared code.  That would allow X32 support without
>> dragging in all of the 32-bit compat support.  I never finished it because I
>> couldn't find a current distribution that supported X32 out of the box to test
>> with.
>
> So yes, x32 support outlined some of the shortcomings of our current compat code,
> which pretty much assumes that there's just a single compat model - which is far
> away from reality on x86, which has 3 compat modes:
>
>  - 16-bit registers, 16-bit memory model (vm86 mode)
>  - 32-bit registers, 32-bit memory model (CONFIG_COMPAT)
>  - 64-bit registers, 32-bit memory model (CONFIG_X86_X32_ABI)
>
> and both the naming and (necessarily) the organization of the code is suffering a
> bit from that currently.
>
> Perhaps we could improve things by reorganizing it along 'multiple ABIs' idiom,
> which x32 partially already started.
>
> The most important aspect of 'compat', in terms of complexity, is pointer size,
> i.e. the memory model. Register width of the ABI matters too, but is mostly
> resolved early on during system call entry. Pointer size details matter all across
> the kernel, in system calls that interact via user-space pointers.
>
>> I agree on dropping the word emulation though, since the hardware provides a
>> full 32-bit environment.  I suggest CONFIG_X86_32_COMPAT (or
>> CONFIG_COMPAT_X86_32) as a new name.
>
> So why not just use CONFIG_COMPAT and allow the configuration of the 3 system call
> ABIs:
>
>  - CONFIG_SYSCALL_ABI_X32
>  - CONFIG_SYSCALL_ABI_32

This would be quite nice -- we could get rid off all the
defined(CONFIG_X86_32) || defined(IA32_EMULATION) checks.

>  - CONFIG_SYSCALL_ABI_64
>
> Where 64-bit is always enabled on 64-bit kernels and ABI_32 is always enabled on
> 32-bit kernels.
>
> ABI_X32 enables the extra system calls that have 64-bit register width but a
> compact 32-bit memory model.
>
> ( I don't think we want CONFIG_ABI_16, because vm86 is really special, it's
>   essentially an early x86 hypervisor implementation with no separate system call
>   ABI. )

Agreed.

--Andy
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