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D) Scared that disclosing microarchitectural details will open them up to more patent fights that they have to pay off without a lot of benefit to endusers or d

D) Scared that disclosing microarchitectural details will open them up to more patent fights that they have to pay off without a lot of benefit to endusers or developers. E) All of the above

marcan_42 6y ago
E) Because they are doing things nobody else is allowed to (extending the ARMv8-A instruction set outside of the implementation-defined register mechanism, and blatantly breaking ARM architectural requirements like hard-coding VHE mode to on), and ARM lawyers are on the edge of their seats. No, really, Apple are going out of their way not to document certain details about the M1, and this is almost certainly the reason. ARM are scared to death of fragmentation, Apple somehow managed to get away with doing it anyway, and ARM do not want anyone else to get any ideas.
- monocasa 6y ago
  If Apple cared what ARM thought, they would have finished implementing the spec. AArch64 is as much Apple's as it is ARM's and I doubt they're scared. They have a do wtf you want license and ultimately don't really care if the rest of ARM withers and dies.
  - marcan_42 6y ago
    There is no such "do wtf you want" license. The ARM architectural license allows licensees (like Apple, Cavium, Samsung, and others) to implement CPUs that comply with the architecture. Some things are off-limits, like custom instructions. Apple broke those rules. They probably got away with doing that as a "special exception" under the understanding that they were doing so for "embedded" use cases, i.e. iOS devices that will only ever run iOS, but now that their designs are in an open platform (M1), things have changed, and ARM is not happy.
    - monocasa 6y ago
      Apple literally designed large parts of AArch64. There's no do wtf you want license that you can go out and buy, but Apple has one none the less from the sheer fact that it's partially their's to begin with and they negotiated it with ARM before AArch64 was even a twinkle in their eyes. ARM probably has some trademark mechanisms that they could in some world use to enforce compliance from Apple, but Apple has been super duper careful to refer to it as Apple Silicon rather than ARM.
    - skissane 6y ago
      > There is no such "do wtf you want" license How do you know? ARM's license agreements with Apple are confidential and just about nobody knows what's actually in them (and the few who have seen them aren't allowed to talk about it.) The standard terms which ARM offers to its other customers may be quite different from the terms it has negotiated with Apple. Apple is a customer with unique clout and leverage, which means they can extract terms in negotiations which other customers may not be able to. If ARM offers Apple (or any other customer) "special terms", it wants to keep that fact confidential, so that other customers who have the (less generous) standard terms don't start pressuring for special terms for them as well.
      - marcan_42 6y ago
        I know, because Apple went through the trouble of close-sourcing the M1 bring-up code in XNU source dumps... because it suddenly contains secret new instructions, while until now ARM XNU builds were largely public. These instructions enable an entire new set of parallel execution modes, among other things, to run more protected kernel code. Completely nonstandard stuff. Also, Apple somehow managed to push custom kernel support to the documentation of kmutil, but not the actual binary, until several macOS releases later. That would only happen if the latter got pulled for some extraneous reason. I've been working on this since December; the entire situation is all showing signs pointing straight at ARM's lawyers having gotten involved to some extent.
        monocasa 6y ago
- skissane 6y ago
  It is at least possible (if not likely) that Apple has a special deal with ARM that lets them get away with all this. Which may mean that ARM wants them to be quiet about. Not because Apple is breaking the rules, but because ARM doesn't want to rub into its other customers the fact that Apple has a special deal that other customers aren't being offered.
  - saagarjha 6y ago
    This sounds the most likely, tbh. Apple has been breaking the spec for years, but they’ve been very testy about ever mentioning their custom extensions and ARM has probably agreed to look the other way as long as they don’t draw attention to the fact.
    - skissane 6y ago
      > ARM has probably agreed to look the other way as long as they don’t draw attention to the fact That makes it sound like it is some kind of "tacit understanding", "I won't say anything if you don't say anything". I'm suggesting that maybe Apple's license agreement explicitly states that they are allowed to do all this, but also maybe its confidentiality clauses prohibit either party from publicly acknowledging that fact without the other party's explicit permission. A company like Apple – who has a well-funded legal department, and I've never heard any suggestion that they are anything other than competent – wouldn't set up a multi-billion dollar business on the foundation of "agreed to look the other way". They'd have it all set out in writing, crystal clear and totally secret.
    - marcan_42 6y ago
      The difference is until now nobody could use those extensions, especially all the kernel mode stuff. Now they can, since the M1 is an open platform (running third-party kernel code is supported).
      - monocasa 6y ago
        AMX on the A13 was available from EL0 with no real issues.
- davidw 6y ago
  I am old enough to remember the "good old days" when there were OS/chip pairs from all the big companies. IBM, Sun, HP, SGI, DEC all had their own Unix versions that ran on their own hardware. That's part of the reason that tools like 'configure' are so ugly.

D) Scared that disclosing microarchitectural details will open them up to more patent fights that they have to pay off without a lot of benefit to endusers or developers. E) All of the above

marcan_42 6y ago

E) Because they are doing things nobody else is allowed to (extending the ARMv8-A instruction set outside of the implementation-defined register mechanism, and blatantly breaking ARM architectural requirements like hard-coding VHE mode to on), and ARM lawyers are on the edge of their seats. No, really, Apple are going out of their way not to document certain details about the M1, and this is almost certainly the reason. ARM are scared to death of fragmentation, Apple somehow managed to get away with doing it anyway, and ARM do not want anyone else to get any ideas.

monocasa 6y ago
If Apple cared what ARM thought, they would have finished implementing the spec. AArch64 is as much Apple's as it is ARM's and I doubt they're scared. They have a do wtf you want license and ultimately don't really care if the rest of ARM withers and dies.
- marcan_42 6y ago
  There is no such "do wtf you want" license. The ARM architectural license allows licensees (like Apple, Cavium, Samsung, and others) to implement CPUs that comply with the architecture. Some things are off-limits, like custom instructions. Apple broke those rules. They probably got away with doing that as a "special exception" under the understanding that they were doing so for "embedded" use cases, i.e. iOS devices that will only ever run iOS, but now that their designs are in an open platform (M1), things have changed, and ARM is not happy.
  - monocasa 6y ago
    Apple literally designed large parts of AArch64. There's no do wtf you want license that you can go out and buy, but Apple has one none the less from the sheer fact that it's partially their's to begin with and they negotiated it with ARM before AArch64 was even a twinkle in their eyes. ARM probably has some trademark mechanisms that they could in some world use to enforce compliance from Apple, but Apple has been super duper careful to refer to it as Apple Silicon rather than ARM.
  - skissane 6y ago
    > There is no such "do wtf you want" license How do you know? ARM's license agreements with Apple are confidential and just about nobody knows what's actually in them (and the few who have seen them aren't allowed to talk about it.) The standard terms which ARM offers to its other customers may be quite different from the terms it has negotiated with Apple. Apple is a customer with unique clout and leverage, which means they can extract terms in negotiations which other customers may not be able to. If ARM offers Apple (or any other customer) "special terms", it wants to keep that fact confidential, so that other customers who have the (less generous) standard terms don't start pressuring for special terms for them as well.
    - marcan_42 6y ago
      I know, because Apple went through the trouble of close-sourcing the M1 bring-up code in XNU source dumps... because it suddenly contains secret new instructions, while until now ARM XNU builds were largely public. These instructions enable an entire new set of parallel execution modes, among other things, to run more protected kernel code. Completely nonstandard stuff. Also, Apple somehow managed to push custom kernel support to the documentation of kmutil, but not the actual binary, until several macOS releases later. That would only happen if the latter got pulled for some extraneous reason. I've been working on this since December; the entire situation is all showing signs pointing straight at ARM's lawyers having gotten involved to some extent.
      - monocasa 6y ago
skissane 6y ago
It is at least possible (if not likely) that Apple has a special deal with ARM that lets them get away with all this. Which may mean that ARM wants them to be quiet about. Not because Apple is breaking the rules, but because ARM doesn't want to rub into its other customers the fact that Apple has a special deal that other customers aren't being offered.
- saagarjha 6y ago
  This sounds the most likely, tbh. Apple has been breaking the spec for years, but they’ve been very testy about ever mentioning their custom extensions and ARM has probably agreed to look the other way as long as they don’t draw attention to the fact.
  - skissane 6y ago
    > ARM has probably agreed to look the other way as long as they don’t draw attention to the fact That makes it sound like it is some kind of "tacit understanding", "I won't say anything if you don't say anything". I'm suggesting that maybe Apple's license agreement explicitly states that they are allowed to do all this, but also maybe its confidentiality clauses prohibit either party from publicly acknowledging that fact without the other party's explicit permission. A company like Apple – who has a well-funded legal department, and I've never heard any suggestion that they are anything other than competent – wouldn't set up a multi-billion dollar business on the foundation of "agreed to look the other way". They'd have it all set out in writing, crystal clear and totally secret.
  - marcan_42 6y ago
    The difference is until now nobody could use those extensions, especially all the kernel mode stuff. Now they can, since the M1 is an open platform (running third-party kernel code is supported).
    - monocasa 6y ago
      AMX on the A13 was available from EL0 with no real issues.
davidw 6y ago
I am old enough to remember the "good old days" when there were OS/chip pairs from all the big companies. IBM, Sun, HP, SGI, DEC all had their own Unix versions that ran on their own hardware. That's part of the reason that tools like 'configure' are so ugly.