Zig equivalent of gcc used attribute

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1

i need to a force an interrupt handler function to remain in the compiled output – even though it appears not to be used… the function itself is marked export within its container module, where it is being referenced by a C-based interrupt vector table…

here’s the tricky part: i have ModA which imports ModB – where ModB itself contains the exported interrupt handler function…

while my current program directly/indirectly imports ModA, none of its functions are called… as a consequence, ModB effectively disappears from the final executable… other than ModA, no one else has imported ModB…

one approach sometimes used with interrupt handlers is to define so-called “weak” symbols, which would allow me to have a default handler for any not explicitly surviving in the final image…

does zig have “weak” definitions??? or does zig have an equivalent to the gcc “used attribute” ???

2

maybe you are looking for that :slight_smile:

https://ziglang.org/documentation/master/std/#std.mem.doNotOptimizeAway

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3

i would up using “weak” functions in my C code (where my interrupt vector is currently initialized)…

doNotOptimizeAway undoubtedly will prove useful in other scenarios…

in the meanwhile, is there a zig equivalent of “weak” references???

4

If I understand what you are looking for here, you want something that has a default definition that can be overwritten at some other point if you choose to implement it (aka, there’s a name collision).

There are… analogous… things. In the master std file there is a thing called “options”. It first checks if the root has it declared and if not will provide a default implementation… you can see it here: zig/lib/std/std.zig at master · ziglang/zig · GitHub

In terms of having a symbol defined somewhere that you can overwrite in the case of a name collision, I can’t think of one at the moment. I don’t even believe that weak symbols are mentioned in the c standard either.

I’m sure with enough elbow grease, you can make your import structure turing complete though, lol.

5

wikipedia has a nice summary…

and while it is NOT part of the standard, i haven’t encountered a C compiler (gcc, clang, iar, keil, …) that doesn’t have support in their linker…

in my case, i little amount of “C glue” contain weak symbols and their defaults goes a long way… in fact, my actual interrupt routines (as well as the default handler) are written as zig export pub functions…

6

Yes

comptime {
    @export(zigDeclarationToExport, .{ .name = "symbol_name", .linkage = .weak });
}
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7

c++ requires them. The “inline” keyword hasn’t meant inline for years and now basically creates weak symbols (because of the One Definition Rule and how it interacts with header files).

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