With regards to 1), do not write/read structs directly to/from files. Instead write a proper serializer/deserializer. Without it, you may encounter another breakage soon when a different compiler/compiler options insert different struct padding bytes, which will then once again make your data non-portable, and a maliciously crafted save file with no length/size field validation on the deserializer level can lead to a variety of memory bugs.
struct layout is well specified, it should be possible to avoid any padding issues by just aligning and by padding (with dummy members) correctly. The problem in practice is mostly integer representation (big-endian vs little-endian).
Specified by whom? Not the C standard for sure. It is indeed soecified by individual ABIs, and ABIs don't tend to do anything too weird, but that's another question.
1: Letting your code break on pointer size changes is a quite bad sign imho (it's a sign that many other things are probably done with aliasing,etc and has a high risk of breaking due to undefined behaviour once gcc/clang gets around to utilizing it for an optimization).
2: iirc WASM was initially designed to be shimmable via Asm.JS to force laggards(Apple, Google) to implement it, Asm.JS in turn relied on specific rules in JS to get reliable 32bit arithmetic (but impossible for 64bit).
Wasm64 is implemented and works in Chrome and Firefox.. Apple is lagging again with Safari.
1: True, although it also limits the addressable memory and the typical 4GB limit seems less these days. I’m thinking of large apps like Figma running in the browser.
2: Will existing 32-bit WASM binaries break on WASM64 engines or does the binary have a flag for compatibility?
1: Something like Figma could probably offload some of the memory pressure to GPU textures. (But they'd probably run into safety browser limits before that).
2: Most runtimes are 64bit already, A runtime detecting a wasm32 binary will just continue to generate code with the current JIT compiler whilst WASM64 will require another JIT (and perhaps memory system since WASM32 runtimes are often based on "hacks" where 4gb of address space is reserved but not given real memory so that the JIT compiler gets an easier job without security implications).
I believe 32-bit was chosen partially due to implementation efficiency reasons. It makes sense because you can allocate a 4GB mapping, so there is no need for a second software virtual memory layer. Also perhaps they internally require tagged pointers, which are much cheaper, especially if aligned, if the pointer is only 32 bits
32 is better for a lot of things like simd. the strength of it is wasm can do both types now and js can't unfortunately. a number in js is strictly 64.
I love how WASM is the thing that finally blurred the line between Web and Native programming, formely two realms isolated from each other for a long time. This both develops better awareness of how the code is executed by the hardware, which JavaScript devs often lack, and also brings skilled folks from the Native platforms who seem to be not so against WASM as they were against JavaScript (and all other parts of the Web, really). Maybe this will bear fruit in that people will make more Native user interfaces again.
I wanted to love it. As someone who hasn't done any web stuff since I was a child, I thought it'd amazing for it to be "just another platform".
I'm a bit disappointed though:
* There's still no way to do DOM manipulation. So then it's tempting to just grab a canvas and draw everything yourself, which of course wreaks on things like accessibility. I'm no fan of the web, but at least it comes with a somewhat agreed-upon way to display graphical stuff – it's a bit of a shame if we're all gonna just treat it like a surface for pixels.
* WASI still leaves something to be desired. Why can't I have raw sockets and file access and stuff, in a POSIX-like way? I understand that sandboxing is important, so this can all be on a per-request-basis, but still. This "just another platform" is still too far from just that.
* The amount of JS glue needed to actually load WASM stuff in the browser is annoying. The idea of needing a bunch of magic "bundlers" is sad.
> WASI still leaves something to be desired. Why can't I have raw sockets and file access and stuff, in a POSIX-like way?
FWIW, that's exactly what they shipped first, with WASI preview 1 (wasip1). You can still use this today, and all runtimes with any level of WASI support will be able to run it.
If enough people adopt identical or similar js glue then they can use that for a new standard. If people dont care about a standard interface then why both creaing a new standard? Look what happened with jquery selectors and ajax. People loved it and it became the new standard built into browsers.
You can call JS in which you can manipulate the DOM.
Of course architecturally (also regarding your file access) it's better to use the wasm for logic as much as possible where the web (HTML/JS) provides the UI and IO, data flows into wasm for work and results flow back to the web.
This also has the benefit that you can keep your original C/C++ source code much more platform agnostic which helps reusability and testing.
> You can call JS in which you can manipulate the DOM.
Well sure. But for me, the promise of WASM was to make the browser "just another platform". Now it's "this special platform where you have to access some of the most important functionality through FFI interop with a very high-level, very opinionated language".
> Of course architecturally (also regarding your file access) it's better to use the wasm for logic as much as possible where the web (HTML/JS) provides the UI and IO, data flows into wasm for work and results flow back to the web.
OK, but like, I wanted the browser to be "just another platform". I don't want to use JS, and I consider HTML orthogonal to my logic. I realize that's not where we're at, but that's what I dreamt of. Hence my disappointment. Which is OK, I don't matter :)
> This also has the benefit that you can keep your original C/C++ source code much more platform agnostic which helps reusability and testing.
There's no way to draw on a canvas in WASM either. You just decided to write JS wrapper functions for that. But you didn't write wrapper functions for DOM manipulation.
It's not 100% better, but it cuts out a few tokens which helps readability and moves the significant asterix further left where I think it's easier to spot.
Maybe I find this harder to parse because I'm not used to sizeof without brackets (though I know it's valid). But I think the bigger deal is that your version has a bug if the star is missing whereas there's has a bug if the star is present; it's easier to spot something extra than it is to spot something missing.
It's slower. Wasm32 can just reserve 8 GiB (32-bit pointer + 32-bit offset) of the virtual address space from the OS for each memory, so checking for out-of-bounds memory accesses imposes no performance penalty. Wasm64 can't do that, so each memory access is a bit slower.
Sometimes I wonder whether it's possible to run the wasm code in a separate sandboxed process to eliminate a lot of checks. I mean optionally, because normally JS calls wasm code synchronously in the same address space. The bridge will add more latency when there is a transition between JS and wasm. It's obviously complicated because some data structures can also be shared, such as SharedArrayBuffer.
Oh that's interesting, never noticed it in my experience but I have never written anything in wasm where it would matter. Makes perfect sense now that I think about it though. Thanks!
You don't need 4GB and it wastes memory to make pointers twice as big? Even Linux supports running 64-bit code in a 32-bit address space ("x32 ABI") for this reason.
With regards to 1), do not write/read structs directly to/from files. Instead write a proper serializer/deserializer. Without it, you may encounter another breakage soon when a different compiler/compiler options insert different struct padding bytes, which will then once again make your data non-portable, and a maliciously crafted save file with no length/size field validation on the deserializer level can lead to a variety of memory bugs.
struct layout is well specified, it should be possible to avoid any padding issues by just aligning and by padding (with dummy members) correctly. The problem in practice is mostly integer representation (big-endian vs little-endian).
Specified by whom? Not the C standard for sure. It is indeed soecified by individual ABIs, and ABIs don't tend to do anything too weird, but that's another question.
Why is a relatively new technology like WASM being limited to 32-bit pointers? Why repeat the same mistake again?
> Web is 32-bit. Your 64-bit structs will break. This was the root cause of most of my bugs. WASM is 32-bit address space, pointers are 4 bytes not 8.
1: Letting your code break on pointer size changes is a quite bad sign imho (it's a sign that many other things are probably done with aliasing,etc and has a high risk of breaking due to undefined behaviour once gcc/clang gets around to utilizing it for an optimization).
2: iirc WASM was initially designed to be shimmable via Asm.JS to force laggards(Apple, Google) to implement it, Asm.JS in turn relied on specific rules in JS to get reliable 32bit arithmetic (but impossible for 64bit).
Wasm64 is implemented and works in Chrome and Firefox.. Apple is lagging again with Safari.
Thanks!
1: True, although it also limits the addressable memory and the typical 4GB limit seems less these days. I’m thinking of large apps like Figma running in the browser.
2: Will existing 32-bit WASM binaries break on WASM64 engines or does the binary have a flag for compatibility?
1: Something like Figma could probably offload some of the memory pressure to GPU textures. (But they'd probably run into safety browser limits before that).
2: Most runtimes are 64bit already, A runtime detecting a wasm32 binary will just continue to generate code with the current JIT compiler whilst WASM64 will require another JIT (and perhaps memory system since WASM32 runtimes are often based on "hacks" where 4gb of address space is reserved but not given real memory so that the JIT compiler gets an easier job without security implications).
what would make it break? i think the program just calls a 64 bit wasm memory function if it uses the capability
I believe 32-bit was chosen partially due to implementation efficiency reasons. It makes sense because you can allocate a 4GB mapping, so there is no need for a second software virtual memory layer. Also perhaps they internally require tagged pointers, which are much cheaper, especially if aligned, if the pointer is only 32 bits
WASM has a (pointer + i32) address mode, and the effective address is 33 bits. So WASM implementations use 8GB mappings ...
32 is better for a lot of things like simd. the strength of it is wasm can do both types now and js can't unfortunately. a number in js is strictly 64.
Because a web page shouldn’t use 4 GB of ram, and the win is that each pointer can be half the size (better for memory and cache).
The real mistake is requiring pointer to be 64 bit when most programs don’t use it.
I love how WASM is the thing that finally blurred the line between Web and Native programming, formely two realms isolated from each other for a long time. This both develops better awareness of how the code is executed by the hardware, which JavaScript devs often lack, and also brings skilled folks from the Native platforms who seem to be not so against WASM as they were against JavaScript (and all other parts of the Web, really). Maybe this will bear fruit in that people will make more Native user interfaces again.
ActiveX, Alchemy, PNaCL,...
JVM, Z-Machine, P-Code.
I wanted to love it. As someone who hasn't done any web stuff since I was a child, I thought it'd amazing for it to be "just another platform".
I'm a bit disappointed though:
* There's still no way to do DOM manipulation. So then it's tempting to just grab a canvas and draw everything yourself, which of course wreaks on things like accessibility. I'm no fan of the web, but at least it comes with a somewhat agreed-upon way to display graphical stuff – it's a bit of a shame if we're all gonna just treat it like a surface for pixels.
* WASI still leaves something to be desired. Why can't I have raw sockets and file access and stuff, in a POSIX-like way? I understand that sandboxing is important, so this can all be on a per-request-basis, but still. This "just another platform" is still too far from just that.
* The amount of JS glue needed to actually load WASM stuff in the browser is annoying. The idea of needing a bunch of magic "bundlers" is sad.
> WASI still leaves something to be desired. Why can't I have raw sockets and file access and stuff, in a POSIX-like way?
FWIW, that's exactly what they shipped first, with WASI preview 1 (wasip1). You can still use this today, and all runtimes with any level of WASI support will be able to run it.
If enough people adopt identical or similar js glue then they can use that for a new standard. If people dont care about a standard interface then why both creaing a new standard? Look what happened with jquery selectors and ajax. People loved it and it became the new standard built into browsers.
You can call JS in which you can manipulate the DOM.
Of course architecturally (also regarding your file access) it's better to use the wasm for logic as much as possible where the web (HTML/JS) provides the UI and IO, data flows into wasm for work and results flow back to the web.
This also has the benefit that you can keep your original C/C++ source code much more platform agnostic which helps reusability and testing.
> You can call JS in which you can manipulate the DOM.
Well sure. But for me, the promise of WASM was to make the browser "just another platform". Now it's "this special platform where you have to access some of the most important functionality through FFI interop with a very high-level, very opinionated language".
> Of course architecturally (also regarding your file access) it's better to use the wasm for logic as much as possible where the web (HTML/JS) provides the UI and IO, data flows into wasm for work and results flow back to the web.
OK, but like, I wanted the browser to be "just another platform". I don't want to use JS, and I consider HTML orthogonal to my logic. I realize that's not where we're at, but that's what I dreamt of. Hence my disappointment. Which is OK, I don't matter :)
> This also has the benefit that you can keep your original C/C++ source code much more platform agnostic which helps reusability and testing.
It feels the opposite to me.
There's no way to draw on a canvas in WASM either. You just decided to write JS wrapper functions for that. But you didn't write wrapper functions for DOM manipulation.
You're right. But at least the JS wrapper for the canvas is just used for setting up the shared memory, if I remember correctly?
At any rate: this doubly makes my point.
Meta: a space is missing in the title.
Since this is one of the bugs, I always recommemd writing
Like this instead: It's not 100% better, but it cuts out a few tokens which helps readability and moves the significant asterix further left where I think it's easier to spot.It's totally true, using sizeof like a function is one of my pet peeves. Even the kernel people do it but it's WRONG and you are right.
But ACSHUALLY, how you write allocation is like this
The kernel people seem to finally have figured out this one in 2026.> Meta: a space is missing in the title.
I like the word "everybug" :-D
Honestly, I think I'm more likely to get your form wrong than the original one. This doesn't obviously look wrong to me:
Maybe I find this harder to parse because I'm not used to sizeof without brackets (though I know it's valid). But I think the bigger deal is that your version has a bug if the star is missing whereas there's has a bug if the star is present; it's easier to spot something extra than it is to spot something missing.Fun game! The demo works great on mobile except for some small font sizes and you can't hover over items to see the tooltip before selecting them.
The memory64 proposal was merged into upstream last year, any reason to opt into 32 bit despite that?
It's slower. Wasm32 can just reserve 8 GiB (32-bit pointer + 32-bit offset) of the virtual address space from the OS for each memory, so checking for out-of-bounds memory accesses imposes no performance penalty. Wasm64 can't do that, so each memory access is a bit slower.
Sometimes I wonder whether it's possible to run the wasm code in a separate sandboxed process to eliminate a lot of checks. I mean optionally, because normally JS calls wasm code synchronously in the same address space. The bridge will add more latency when there is a transition between JS and wasm. It's obviously complicated because some data structures can also be shared, such as SharedArrayBuffer.
Oh that's interesting, never noticed it in my experience but I have never written anything in wasm where it would matter. Makes perfect sense now that I think about it though. Thanks!
You don't need 4GB and it wastes memory to make pointers twice as big? Even Linux supports running 64-bit code in a 32-bit address space ("x32 ABI") for this reason.
> Even Linux supports running 64-bit code in a 32-bit address space ("x32 ABI") for this reason.
I don't think that ever had much, if any, adoption and it looks like it will be removed in the next few releases.
Apple
they limit some good things on purpose just for the sake of ecosystem competition. but with this they are slowly implementing it?
Probably a firefox bug but the interface hit boxes are misaligned when fullscreen
If you are porting anything from C into WebAssembly, keep in mind that you still inherit C based vulnerabilities. [0] [1]
[0] https://soft.vub.ac.be/Publications/2022/vub-tr-soft-22-02.p...
[1] https://www.usenix.org/system/files/sec20-lehmann.pdf
which of these vulnerabilities are most concerning to you in wasm programs?
Also https://00f.net/2018/11/25/webassembly-doesnt-make-unsafe-la...
No worries, it is sandboxed. /s
i want to hack 99 night in the forest