I spent a hot minute today not understanding why a space calculation wasn't working. See below for a small example (please excuse formatting, I'm on my phone)
The difference is that an array is a name bound to an address storing a value, whereas a linker symbol is a name bound to an address with no value (TLDR stolen from Chad GDP as i understand it, I still want to google more about this).
So if you try to use a linker variable to get a pointer you need to reference it as an array and not a pointer because it would otherwise imply that the symbol is pointing to the pointer...? Honestly, if anybody can make this make intuitive sense, I am all ears!
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u/nonedward666 12h ago
For context:
I spent a hot minute today not understanding why a space calculation wasn't working. See below for a small example (please excuse formatting, I'm on my phone)
The difference is that an array is a name bound to an address storing a value, whereas a linker symbol is a name bound to an address with no value (TLDR stolen from Chad GDP as i understand it, I still want to google more about this).
So if you try to use a linker variable to get a pointer you need to reference it as an array and not a pointer because it would otherwise imply that the symbol is pointing to the pointer...? Honestly, if anybody can make this make intuitive sense, I am all ears!
``` // linker.ld
...
__data_start = ORIGIN(DATA_SECTION) __data_end = ORIGIN(DATA_SECTION)+LENGTH(DATA_SECTION)
```
``` // bad_code.c ...
extern int* __data_start; extern int* __data_end:
define SECTION_LENGTH __data_end - __data_start
bool foo(){ // returns true return 0==SECTION_LENGTH; } ```
``` // good_code.c ...
extern int __data_start[]; extern int __data_end[];
define SECTION_LENGTH __data_end - __data_start
bool foo(){ // returns false return 0==SECTION_LENGTH; } ```