4 ms·

I honestly can't tell if you know a lot more than me or a lot less than me about how computers work... A couple of honest questions: 1. Where do you save the c

by 0xffff2 10mo ago

I honestly can't tell if you know a lot more than me or a lot less than me about how computers work... A couple of honest questions: 1. Where do you save the current value of the return address register before calling a function? 2. When parameters are "grouped into a structure" and the structure is passed as an argument to a function, where do you store that structure?

RealityVoid 10mo ago
Not OP, but presumably, the answers are: 1) You don't... hence, my question about no nested function calls. If you push it anywhere else, you can call it whatever you want, but you just re-invented the stack. I _guess_ you could do some wierd stuff to technically not get a stack, but... again, it's wierd. And for what, again? 2) Some fixed address. If you have for example: ```c typeRealBigStructure foo; void baz(typeRealBigStructure * struct){ // Do whatever to struct } void bar(void){ baz(&foo); } ``` The foo will probably end up in the BSS and will take up that space for the whole lifetime of the program. That's not the heap, not the stack, just... a fixed location in memory where the linker placed it. I guess on big PC's stuff is very dynamic and you use malloc for a lot of stuff, but in embedded C, it's a very common pattern.
- 0xffff2 10mo ago
  Ah, you're right, the struct case is actually pretty straightforward (especially since recursion is likely forbidden anyway), I just have trouble contorting my brain to such a different viewpoint.
quietbritishjim 10mo ago
The sibling comment already answered your question, but just to add: As I mentioned earlier, this was actually how old programming languages worked. Famously(ish), Dijkstra secretly snuck recursive functions into the ALGOL 60 standard, thus forcing compiler authors to use a stack! https://news.ycombinator.com/item?id=10131664 https://news.ycombinator.com/item?id=10131664

by 0xffff2 10mo ago

RealityVoid 10mo ago

Not OP, but presumably, the answers are: 1) You don't... hence, my question about no nested function calls. If you push it anywhere else, you can call it whatever you want, but you just re-invented the stack. I _guess_ you could do some wierd stuff to technically not get a stack, but... again, it's wierd. And for what, again? 2) Some fixed address. If you have for example: ```c typeRealBigStructure foo; void baz(typeRealBigStructure * struct){ // Do whatever to struct } void bar(void){ baz(&foo); } ``` The foo will probably end up in the BSS and will take up that space for the whole lifetime of the program. That's not the heap, not the stack, just... a fixed location in memory where the linker placed it. I guess on big PC's stuff is very dynamic and you use malloc for a lot of stuff, but in embedded C, it's a very common pattern.

0xffff2 10mo ago
Ah, you're right, the struct case is actually pretty straightforward (especially since recursion is likely forbidden anyway), I just have trouble contorting my brain to such a different viewpoint.

quietbritishjim 10mo ago

The sibling comment already answered your question, but just to add: As I mentioned earlier, this was actually how old programming languages worked. Famously(ish), Dijkstra secretly snuck recursive functions into the ALGOL 60 standard, thus forcing compiler authors to use a stack! https://news.ycombinator.com/item?id=10131664 https://news.ycombinator.com/item?id=10131664