5 ms·

Most of the problems exposed here aren't C related, but OS or architecture related. An ABI where function parameters are passed over A, B, and C registers and t

by jmrm 5y ago

Most of the problems exposed here aren't C related, but OS or architecture related. An ABI where function parameters are passed over A, B, and C registers and the return value is stored in the Z register have nothing to do with any language.

saagarjha 5y ago
Ok, but the way this is exposed is via C so you really have to figure out what it is going to do to use it.
dzaima 5y ago
Except that C defines the way nearly everything everywhere passes function parameters over registers. Not C's fault, but still a thing affecting everyone that doesn't write C, as C doesn't even try to be a good ABI, because it wasn't meant to be.
- mek6800d2 5y ago
  What does this mean? C defines the mechanism(s) for passing arguments to a function? That's news to me. The parent's point was that the binary mechanisms are OS- and architecture-dependent. (And compiler-/build-dependent too; e.g., when compilers are designed to pass arguments via registers rather than on a stack.) As other commenters have tried to point out, the diversity of target platforms precludes a single, one-size-fits-all ABI -- for C or for any other language. How does a language "try to be a good ABI"? An example of such a language would help.
  - dzaima 5y ago
    C itself doesn't, but the OS deciding how it interfaces with C quickly results in all C programs for that OS doing the same thing, and, since C is the lingua franca of programming languages, in every single program with a cross-language API. An ABI doesn't need to be a language. In fact, I'd say that makes it worse, as now you'd have a potentially conflicting goal, wanting to make it nicer for the language itself, possibly at the cost of making for a worse ABI. But one could do well with not having varying width integers (looking especially at you, "long"), having a defined structure layout, and one (primary) calling convention per architecture (it not being the absolute best if goals change would be fine, as it'd only be used to talk between different languages, and that usually doesn't happen with such a frequency that a couple nanoseconds hurt). Sure, you'd still end up with some variance, but it'd be a lot easier to work with, and it'd be pretty hard to reach the count of 176 ABIs of C. edit: ..and just not defining things that aren't actually related to ABI (or may need to change), i.e. intmax_t
- lelanthran 5y ago
  > Except that C defines the way nearly everything everywhere passes function parameters over registers. I don't think that that is correct. Sure, your C implementation defines which params go into which register in a certain way, but other C implementations define the same thing in a different way.

by jmrm 5y ago

saagarjha 5y ago

Ok, but the way this is exposed is via C so you really have to figure out what it is going to do to use it.

dzaima 5y ago

Except that C defines the way nearly everything everywhere passes function parameters over registers. Not C's fault, but still a thing affecting everyone that doesn't write C, as C doesn't even try to be a good ABI, because it wasn't meant to be.

mek6800d2 5y ago
What does this mean? C defines the mechanism(s) for passing arguments to a function? That's news to me. The parent's point was that the binary mechanisms are OS- and architecture-dependent. (And compiler-/build-dependent too; e.g., when compilers are designed to pass arguments via registers rather than on a stack.) As other commenters have tried to point out, the diversity of target platforms precludes a single, one-size-fits-all ABI -- for C or for any other language. How does a language "try to be a good ABI"? An example of such a language would help.
- dzaima 5y ago
  C itself doesn't, but the OS deciding how it interfaces with C quickly results in all C programs for that OS doing the same thing, and, since C is the lingua franca of programming languages, in every single program with a cross-language API. An ABI doesn't need to be a language. In fact, I'd say that makes it worse, as now you'd have a potentially conflicting goal, wanting to make it nicer for the language itself, possibly at the cost of making for a worse ABI. But one could do well with not having varying width integers (looking especially at you, "long"), having a defined structure layout, and one (primary) calling convention per architecture (it not being the absolute best if goals change would be fine, as it'd only be used to talk between different languages, and that usually doesn't happen with such a frequency that a couple nanoseconds hurt). Sure, you'd still end up with some variance, but it'd be a lot easier to work with, and it'd be pretty hard to reach the count of 176 ABIs of C. edit: ..and just not defining things that aren't actually related to ABI (or may need to change), i.e. intmax_t
lelanthran 5y ago
> Except that C defines the way nearly everything everywhere passes function parameters over registers. I don't think that that is correct. Sure, your C implementation defines which params go into which register in a certain way, but other C implementations define the same thing in a different way.