Calculating size of function

[0152la]

Suppose we have a function definition, in either C or assembly. Is it possible to calculate the size of such a function (presumably in byes) at compile time? One potential solution would be to have the functions whose sizes we want to calculate in a separate file, compile it, and perform the computation based on ELF data, but are there maybe easier solutions?

[ltratt]

@vext01 might have some ELF-ish thoughts about this?

[jacobbramley]

A typical method (e.g. used by clang and others) is to define a (local) symbol at the end of the function and set .size based on arithmetic. For example:

    .globl  func
    .p2align        2
    .type   func,@function
func:
    ...
    ret
.Lfunc_end0:
    .size    func, .Lfunc_end0-func

It might not be feasible to read that from source — I've never tried — but for assembly functions you can define a global symbol (instead of the local .Lfunc_end0) or perhaps calculate the size and store it as some other global constant.

[0152la]

An approach of doing this was implemented in #55. Do we still want to keep this issue for potential future improvements to the current implementation?

[jacobbramley]

In principle we could do better — making it a static constant with a relocation — but whether or not that is achievable is unclear. It's probably a low priority concern, anyway.