alt Hacker NewsI think this is a fine post. But one comment:
> remember that for compilers which emit machine code, like roc and rustc, doing memory-unsafe things is a big part of the job
I don't really think that this is true, in the way that it's written.
I think that for the hot binary patching / code reloading features, yes, that is going to need unsafe. But for regular old "producing an executable" compilation? Emitting machine code isn't the part that requires unsafe. The language's runtime is a more likely site to find unsafe.
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Many people try to twist the fact memory safe languages have unsafe code blocks to make the pivot that why bother.
It is like someone arguing that since they always bump the head somehow while wearing seatbelts, then they are only a nuisance and should not be used.
Yeah that is definitely 1000% wrong. A compiler can do its job with totally abstract data structures. If anything would need to do unsafe stuff in memory, it would probably be a linker.
I agree that it’s not inherent to emitting machine code but I do think it reflects a different set of priorities.
In extremely high performance code you use different data structures and algorithms and change your approach to memory allocation. TigerBeetle famously does all memory allocation once on startup.
Roc is attempting to make a similar set of trade-offs in their compiler as Zig, so it makes sense that the author finds many shared patterns.
That line confused me, too. What parts of their compiler require memory-unsafe operations to produce machine code?
I think if you interpret it charitably it means that any bug in the emitted machine code is already a likely memory-unsafe miscompilation if it is ran.
The compiler itself might be perfectly "memory safe" but the generated binary fundamentally is always at risk (besides WebAssembly I suppose).
I'm fully aware of the separation of compiler and binary, and being able to compile untrusted code safely is nice, but a perfectly safe compiler that generates vulnerable binaries isn't that much better.
Agreed, that’s disturbingly incorrect.
If anything, compilers are perfect models of trees and well formed programs.
> I think that for the hot binary patching / code reloading features, yes, that is going to need unsafe. But for regular old "producing an executable" compilation? Emitting machine code isn't the part that requires unsafe. The language's runtime is a more likely site to find unsafe.
Agreed! Emitting machine code is not unsafe, since it's just writing bytes down - it's only once you execute that machine code that there's potentially unsafety. The reason I said "a big part of the job" is that in practice a lot of compilers both emit machine code and execute it - but you're totally right that it's not a requirement that a compiler do both.
In addition to the examples you gave (hot binary patching/code reloading, language runtime, etc.), others would be things like evaluating userspace code at compile time (e.g. const fn in Rust, or in Roc any expression that could be hoisted to the top level), running tests and inspecting their output to decide what to display to the user, etc.
Those are the types of things I had in mind when I wrote that.