6 ms·

While I do agree WASM makes a lot of sense for the Web, I personally am having doubts regarding treating WASM as a general abstractions for native code as used

by xuejie 7y ago

While I do agree WASM makes a lot of sense for the Web, I personally am having doubts regarding treating WASM as a general abstractions for native code as used in the post. For this case, it might suit the job better to have a bytecode that resembles more of underlying machine architecture, rather than a still highly abstracted model like WASM. Please don't get me wrong, I do agree WASM is already one step ahead of, say, JavaScript, but we can do better than that. The problem with WASM here, is that it really is a bloated model like JVM in its early days, huge amount of work is needed to make it closer to native speed, which is contradictory to the original slogan. What's more, people are still planning to add tons of new features to it: https://webassembly.org/docs/future-features/ https://webassembly.org/docs/future-features/. Before you tell me those are opt-in features, the question I want to raise is: for an abstraction of general platform, you would definitely want to have a widely accepted standard so people know what features will be expected, one example is that people know SSE will be available for 64-bit x86 code. With all those opt-in features, I doubt if we can have a proper layer that adapts well to different implementations with different supported features. We might end up with the situation like Rust, where you can claim a secondary compiler could exist, but in practice people are all using the same compiler/implementation.

dmitriid 7y ago
Besides, doesn't LLVM already have an IR which servers as one such higher-level abstraction?
- rapsey 7y ago
  I'm pretty sure it is not stable and not designed for such a use case.
  - pjmlp 7y ago
    Apple kind of disagrees with watchOS bitcode.
    - tom_mellior 7y ago
      "not designed for that use case" != "isn't used for that use case in practice" Apple has tight control over the bitcode version and the target platforms supported by Xcode. That's not the same thing as accepting arbitrary LLVM bitcode files.
      - pjmlp 7y ago
        Nothing prevents LLVM project to adopt such variant, other than unwillingness to do so.
- jcelerier 7y ago
  No, LLVM IR is machine specific. Any "native" language is since the ABI of a struct will depend e.g. on the size of pointers for that platform. E.g. Consider in C int foo[sizeof(void*)];
  - pjmlp 7y ago
    Open source LLVM IR is machine specific, it doesn't have to be, as proven by watchOS bitcode, or PNaCL.
    - saagarjha 7y ago
      Both of the examples you gave were very carefully architected to make sure that was the case.
      - pjmlp 7y ago
        Which doesn't prevent the case of someone contributing back such kind of variants.
    - jcelerier 7y ago
      > it doesn't have to be, as proven by watchOS bitcode, or PNaCL. Both of those have fixed 32-bit pointer sizes and are little-endian. When you compile for watchOS bitcode or PNaCL you just target a single virtual machine & "system" ABI. LLVM IR or any related techniques won't ever allow you to produce a 32 / 64 bit or ARM / x86 app that is able to leverage the whole feature set of the platform from the same bitcode.
      - pjmlp 7y ago
        Yet watchOS migrated from 32 bit to 64 bit. It is possible, LLVM project just needs to actually want to support such use cases in a portable way.
        jcelerier 7y ago
        > Yet watchOS migrated from 32 bit to 64 bit. that is what they said in the press release but in practice they migrated from "classical" 32bit ARM to ILP-32 (akin to the x32 ABI on linux) so the size of pointers, etc etc does not change from 32-bit. You get more registers & stuff like that which is nice, but that is not moving to 64 bit, just having nicer 32 bit execution on 64 bit CPUs. If you want proper aarch64 support on WatchOS you have to recompile.
- jahewson 7y ago
  Google created pretty much this, called it PNaCl and shipped it in Chrome. It now has been retired in favor of WASM.
  - pjmlp 7y ago
    Because Mozilla went political and came up with asm.js as counter technology.
    - afiori 7y ago
      Or as some other (like, eg Google itself) would say: > Because Mozilla went political and came up with asm.js as better technology.
      - pjmlp 7y ago
        I am pretty sure that asm.js would not happened if Chrome already had the market share it enjoys nowadays. WASM is still catching up to PNaCL in performance, hardly better.
  - AndrewDucker 7y ago
    For the reasoning behind this, see https://github.com/WebAssembly/design/blob/master/FAQ.md#why-not-just-use-llvm-bitcode-as-a-binary-format https://github.com/WebAssembly/design/blob/master/FAQ.md#why...
- TazeTSchnitzel 7y ago
  LLVM IR is unstable, way too big in scope, and not as machine-independent as people think. There have been several efforts to use it as a target-independent high-level bytecode, and they either are very platform-specific single-vendor affairs (Apple) or were retired in favour of a simpler new language that doesn't have its problems (SPIR became SPIR-V, PNaCl became WebAssembly).
BiteCode_dev 7y ago
And yet, it will probably be used for that and become popular. Tech doesn't need to be perfect, the best, or even very good to win. They need to have a killer feature and a low cost of adoption. Wasm seems on the right tracker for that.
- xuejie 7y ago
  I totally agree that it's not the best tech always wins, that's why I'm pointing it out, I really wish that 5 years from now, we can rely on something that makes sense to be there, not just because something has a low cost of adoption.
- onebot 7y ago
  > need to have a killer feature and a low cost of adoption This is a powerful statement actually. Could be applied to any tech startup product.
cjbprime 7y ago
It sounds like you're bringing up a register-based vs stack-based VM argument, and claiming that register-based VMs have better performance because their model is closer to the hardware. My understanding is that this intuition is usually untrue, because a JIT benefits from the stack-based code preserving code flow and thus allowing more efficient code generation.
- xuejie 7y ago
  No I'm not talking about register-based vs stack-based VM, that's a totally different topic. I'm just saying WASM is still quite distant from real hardware, making it a non-trivial task to performantly run the code. In fact if you look at the asm.js, which is the original inspiration of WASM, it is a much closer mode to real hardware. And of course JIT can make WASM fast but if you look around, building a performant WASM JIT still remains terribly hard, some implementation even needs LLVM to perform optimizations. I'd say if this is the case, we must've chosen the wrong model.
  - TazeTSchnitzel 7y ago
    Why is it hard? Isn't wasm designed so you can statically and quickly compile pieces of it or the whole thing to native code, rather than needing to do all the tricks dynamic language runtimes do?
    - xuejie 7y ago
      That is their very nice slogan, while in reality WASM still has quite a way to go to compete with native code. Some shits I see these days are that when code speed is measured, people compare that with JS but not native code, when portability is talked about, the comparison is then made against native code, not JS.
  - TomMarius 7y ago
    What major implementations are using LLVM? Firefox is using Cranelift, Chrome is using V8, both of these shouldn't be using LLVM, AFAIK, or am I wrong?
kbumsik 7y ago
> The problem with WASM here, is that it really is a bloated model like JVM in its early days, Isn't WASM (as of its MVP) quite simple VM model compared to other VMs? I agree with your concern about the new futures though. It might introduce another hell of segmentation.
pjmlp 7y ago
That is not an issue regarding bytecode formats in general, given that in some platforms only the kernel does the final compilation to machine code, and they are a common executable format since early 60's. However I do agree with WASM everywhere fashion complaint.
pjc50 7y ago
> bytecode that resembles more of underlying machine architecture In what way? This discussion lacks specifics. Doesn't this also risk tying you to a specific machine, which is the opposite of the intent?

by xuejie 7y ago

dmitriid 7y ago

Besides, doesn't LLVM already have an IR which servers as one such higher-level abstraction?

rapsey 7y ago
I'm pretty sure it is not stable and not designed for such a use case.
- pjmlp 7y ago
  Apple kind of disagrees with watchOS bitcode.
  - tom_mellior 7y ago
    "not designed for that use case" != "isn't used for that use case in practice" Apple has tight control over the bitcode version and the target platforms supported by Xcode. That's not the same thing as accepting arbitrary LLVM bitcode files.
    - pjmlp 7y ago
      Nothing prevents LLVM project to adopt such variant, other than unwillingness to do so.
jcelerier 7y ago
No, LLVM IR is machine specific. Any "native" language is since the ABI of a struct will depend e.g. on the size of pointers for that platform. E.g. Consider in C int foo[sizeof(void*)];
- pjmlp 7y ago
  Open source LLVM IR is machine specific, it doesn't have to be, as proven by watchOS bitcode, or PNaCL.
  - saagarjha 7y ago
    Both of the examples you gave were very carefully architected to make sure that was the case.
    - pjmlp 7y ago
      Which doesn't prevent the case of someone contributing back such kind of variants.
  - jcelerier 7y ago
    > it doesn't have to be, as proven by watchOS bitcode, or PNaCL. Both of those have fixed 32-bit pointer sizes and are little-endian. When you compile for watchOS bitcode or PNaCL you just target a single virtual machine & "system" ABI. LLVM IR or any related techniques won't ever allow you to produce a 32 / 64 bit or ARM / x86 app that is able to leverage the whole feature set of the platform from the same bitcode.
    - pjmlp 7y ago
      Yet watchOS migrated from 32 bit to 64 bit. It is possible, LLVM project just needs to actually want to support such use cases in a portable way.
      - jcelerier 7y ago
        > Yet watchOS migrated from 32 bit to 64 bit. that is what they said in the press release but in practice they migrated from "classical" 32bit ARM to ILP-32 (akin to the x32 ABI on linux) so the size of pointers, etc etc does not change from 32-bit. You get more registers & stuff like that which is nice, but that is not moving to 64 bit, just having nicer 32 bit execution on 64 bit CPUs. If you want proper aarch64 support on WatchOS you have to recompile.
jahewson 7y ago
Google created pretty much this, called it PNaCl and shipped it in Chrome. It now has been retired in favor of WASM.
- pjmlp 7y ago
  Because Mozilla went political and came up with asm.js as counter technology.
  - afiori 7y ago
    Or as some other (like, eg Google itself) would say: > Because Mozilla went political and came up with asm.js as better technology.
    - pjmlp 7y ago
      I am pretty sure that asm.js would not happened if Chrome already had the market share it enjoys nowadays. WASM is still catching up to PNaCL in performance, hardly better.
- AndrewDucker 7y ago
  For the reasoning behind this, see https://github.com/WebAssembly/design/blob/master/FAQ.md#why-not-just-use-llvm-bitcode-as-a-binary-format https://github.com/WebAssembly/design/blob/master/FAQ.md#why...
TazeTSchnitzel 7y ago
LLVM IR is unstable, way too big in scope, and not as machine-independent as people think. There have been several efforts to use it as a target-independent high-level bytecode, and they either are very platform-specific single-vendor affairs (Apple) or were retired in favour of a simpler new language that doesn't have its problems (SPIR became SPIR-V, PNaCl became WebAssembly).

BiteCode_dev 7y ago

And yet, it will probably be used for that and become popular. Tech doesn't need to be perfect, the best, or even very good to win. They need to have a killer feature and a low cost of adoption. Wasm seems on the right tracker for that.

xuejie 7y ago
I totally agree that it's not the best tech always wins, that's why I'm pointing it out, I really wish that 5 years from now, we can rely on something that makes sense to be there, not just because something has a low cost of adoption.
onebot 7y ago
> need to have a killer feature and a low cost of adoption This is a powerful statement actually. Could be applied to any tech startup product.

cjbprime 7y ago

It sounds like you're bringing up a register-based vs stack-based VM argument, and claiming that register-based VMs have better performance because their model is closer to the hardware. My understanding is that this intuition is usually untrue, because a JIT benefits from the stack-based code preserving code flow and thus allowing more efficient code generation.

xuejie 7y ago
No I'm not talking about register-based vs stack-based VM, that's a totally different topic. I'm just saying WASM is still quite distant from real hardware, making it a non-trivial task to performantly run the code. In fact if you look at the asm.js, which is the original inspiration of WASM, it is a much closer mode to real hardware. And of course JIT can make WASM fast but if you look around, building a performant WASM JIT still remains terribly hard, some implementation even needs LLVM to perform optimizations. I'd say if this is the case, we must've chosen the wrong model.
- TazeTSchnitzel 7y ago
  Why is it hard? Isn't wasm designed so you can statically and quickly compile pieces of it or the whole thing to native code, rather than needing to do all the tricks dynamic language runtimes do?
  - xuejie 7y ago
    That is their very nice slogan, while in reality WASM still has quite a way to go to compete with native code. Some shits I see these days are that when code speed is measured, people compare that with JS but not native code, when portability is talked about, the comparison is then made against native code, not JS.
- TomMarius 7y ago
  What major implementations are using LLVM? Firefox is using Cranelift, Chrome is using V8, both of these shouldn't be using LLVM, AFAIK, or am I wrong?

kbumsik 7y ago

> The problem with WASM here, is that it really is a bloated model like JVM in its early days, Isn't WASM (as of its MVP) quite simple VM model compared to other VMs? I agree with your concern about the new futures though. It might introduce another hell of segmentation.

pjmlp 7y ago

That is not an issue regarding bytecode formats in general, given that in some platforms only the kernel does the final compilation to machine code, and they are a common executable format since early 60's. However I do agree with WASM everywhere fashion complaint.

pjc50 7y ago

> bytecode that resembles more of underlying machine architecture In what way? This discussion lacks specifics. Doesn't this also risk tying you to a specific machine, which is the opposite of the intent?