svn commit: r266553 - head/release/scripts
imp at bsdimp.com
Tue May 27 20:31:31 UTC 2014
On May 27, 2014, at 1:40 PM, Tijl Coosemans <tijl at FreeBSD.org> wrote:
> On Tue, 27 May 2014 07:18:06 -0600 Warner Losh wrote:
>> On May 27, 2014, at 1:36 AM, Tijl Coosemans <tijl at FreeBSD.org> wrote:
>>> On Mon, 26 May 2014 16:31:21 -0600 Warner Losh wrote:
>>>> On May 26, 2014, at 4:18 PM, Tijl Coosemans <tijl at FreeBSD.org> wrote:
>>>>> On Mon, 26 May 2014 09:53:57 -0600 Warner Losh wrote:
>>>>>> On May 26, 2014, at 8:39 AM, Nathan Whitehorn <nwhitehorn at freebsd.org> wrote:
>>>>>>> On 05/26/14 02:35, Tijl Coosemans wrote:
>>>>>>>> I suppose you could replace the "x86" in the pkg scheme with i386/amd64,
>>>>>>>> but then you'd still be talking about i386:32, amd64:32 and amd64:64
>>>>>>>> instead of x86:32, x86:x32 and x86:64.
>>>>>> I suppose you could replace these by ?i386?, ?x32? (or ?amd64x32?) and
>>>>>> ?amd64? respectively.
>>>>> So you're on an amd64 or mips64 system (as indicated by uname) but you
>>>>> want to use the 32-bit package if possible. How does your script know
>>>>> about the magic "x32", "amd64x32" or "mipsn32" strings? Wouldn't it be
>>>>> easier if you could just use "`uname -p`:32??
>>>> Oh give me a break. You know it because you know you are building for
>>>> mipsn32 because that?s what you?ve set MACHINE_ARCH or TARGET_ARCH to,
>>> No, MACHINE_ARCH or TARGET_ARCH is "amd64" or "mips64". You are building
>>> the 64-bit OS and then decide separately per package whether you want the
>>> ILP32 one or the LP64 one.
>> I think I understand why we?re talking past each other. This bit is wrong.
>> The LP64 one has a MACHINE_ARCH of ?amd64? or ?mips64?. The ILP32 one will
>> have MACHINE_ARCH of ?i386? or ?mips?. The weird ones (ILP32 with 64-bit
>> registers) will have a different MACHINE_ARCH of ?x32? or ?mipsn32?.
>> Selection can be done on a case by case basis, but this will be validated
>> against the supported_abis sysctl. There?s no need to have different names
>> here, the current standard ones do just fine, are completely sufficient and
>> all inclusive. This is rather by definition, and your understanding of the
>> definition sounds flawed.
>> While we have limited support for building 32-bit binaries, it is to build
>> 32-bit binaries for a different MACHINE_ARCH. -m32 on amd64 creates i386
>> binaries, not amd64:32 binaries. -m32 on powerpc64 creates powerpc binaries,
>> not powerpc64:32 binaries. On mips, -mabi-n32 (I think the option is) is
>> required to create the mipsn32 binaries. In every single one of these cases,
>> there exists a MACHINE_ARCH that completely describes the binary.
> amd64:32 is provided by the -mx32 compiler flag.
True, but not relevant.
>> So I?m still waiting for a use case that requires the new names. One has
>> not been articulated, and I don?t think one actually exists.
> Imagine you've built a system with MACHINE_ARCH amd64 and one with
> MACHINE_ARCH mips64. Now you want to populate these systems with a list
> of packages for which you wrote a script. These systems each support 2
> ABIs: a native 64-bit one (amd64 and mips64) and a native 32-bit one (x32
> and mipsn32). Both are native in the sense that they make full use of the
> instruction set. This is not like i386 on amd64 or mips o32 on mips64
> because those are more like compat shims that operate under special
> (crippled) cpu modes that nobody uses unless they're stuck with old code.
> Both our ABIs on the other hand are native and equally valid and which one
> to use for a particular package depends entirely on the use case. If your
> use case requires more than 4G of address space you'll have to use the
> 64-bit package, otherwise you can use the 32-bit package which, depending
> on how pointer heavy the code is, may give a performance benefit. You
> make this choice for each of the packages in your list and add that
> information to your script.
Long hypothetical, but so what? In such a case, you’d pick one of two different MACHINE_ARCH values depending on the package. This this is a fairly atypical use case, it would not be unreasonable for the person wanting to do this to know the proper companion ABI. In both cases, you have the choice of two other values to use. Which one you use will depend on a variety of factors, and what might be right for one application may be wrong for others.
And in both cases, there’s actually two choices: for amd64, you’d have i386 and x32. Both of these are fine choices, and it would depend on the workload which one is better (i386 has better toolchain support and maturity, x32 offers some interesting theoretical wins, but doesn’t have the same maturity). Same with mips64, you’d have two choices as well. In both cases, you can’t just take uname/MACHINE_ARCH and slap :32 on the end.
> Now let's work with Nathan's patch which uses the following string to
> identify the pkg repository to fetch packages from:
> `uname -s`:`uname -r | cut -f 1 -d .`:`uname -p`
> On our two systems that would be FreeBSD:11:amd64 and FreeBSD:11:mips64.
> Now if your script has to install the 32-bit version of a package how
> can it go from those two strings to FreeBSD:11:x32 or FreeBSD:11:mipsn32
> without a lookup table?
You couldn’t. Which is the whole reason I want to have them have a standard name so you don’t need the lookup table for the common case. This is an “off in the weeds” case, and optimizing for it doesn’t make sense. Especially because in each case, you have two different 32-bit ABIs to choose from. You’d have to have some kind of table in either case. Also, the proper name for n32, in your current system, is mips:32:n32, which (a) is wrong and (b) isn’t regular.
> I say, you can more easily indicate whether you
> want the 32-bit or 64-bit package by appending :32 or :64 to the original
> strings, so FreeBSD:11:amd64:32 and FreeBSD:11:mips64:32.
Except there’s no such thing as mips64:32 in the current system. There’s two different ABIs that could mean. It could be o32 or n32, with the same sort of trade offs. There’d need to be a person in the loop to know, so there’s already a need to have special knowledge. You can’t get there by just adding :32 to the existing thing...
> Like I said in a reply to Nathan's patch, pkg could default to :32 or :64
> for every arch so it can be left out in many cases. FreeBSD:11:i386
> would then be equivalent to FreeBSD:11:i386:32, FreeBSD:11:amd64 to
> FreeBSD:11:amd64:64, etc.
I don’t see what value that adds to have the extra :32 or :64. Nathan’s patches make it possible to have an automated build system with the typical use case (I want to build all my binaries, packages, etc the same). But adding a :32 isn’t going to even work for your hypothetical example because people actually building such systems will need to specify which 32-bit ABI they want to use anyway. And the degenerate case of :32 just doesn’t work with mips…
Consider too that we’re planning a new i386 ABI, which is identical to the current i386 ABI, except time_t is 64 bit. We’ve penciled in the name i386t64 for this ABI/MACHINE_ARCH. This will be much less painful, it is thought, than finding all the current places that take time_t as an arg and shimming… So if we were to do that, then your current scheme wouldn’t be able to encompass that eventuality and we’d be back to this argument...
> This also does not preclude the existence of a mipsn32 MACHINE_ARCH in
> case you want to build a pure mipsn32 system (including the kernel), but
> I wonder how many people would use that if it is possible to have a
> mips64 system run n32 binaries. I don't think many people would run a
> pure x32 system (with x32 kernel) so I don't see the need to have an
> "x32" value for MACHINE_ARCH (or TARGET_ARCH).
Actually, you absolutely must have a x32 MACHINE_ARCH if you want to be able to run x32 binaries. Otherwise, how are you going to build the libraries that use that API? Our build system simply isn’t setup to build them any other way. Although the usr/lib32 stuff could grow extra goo for that, you are still building them the same way you’d build. We have a stylized way to create a sys root, which is needed for the compilers to work. We’d likely have to grow better multi lib support than we have now as well. You’d need some way to identify these binaries, segregate their ld.so, etc. Even if no kernel ever is linked this way, it is still an absolute requirement.
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