Unable to resolve const ptr to function

[justinbalexander]

fn square(num: i32) i32 {
    return num * num;
}

export const vector = []usize {
    @ptrToInt(square),
};

gives error: unable to evaluate constant expression

This works however:

fn square(num: i32) i32 {
    return num * num;
}

export const vector = [](fn (i32) i32) {
    square,
};

The second form won't allow a function pointer with an address of zero and some entries in the vector table on my armv7em processor I believe need to be zero.

This is blocking my progress on making a user-friendly package for arm development on tiva microcontrollers. I have a workaround, but it requires the user to modify a file in the package. I want them to be able to export a function with the correct signature and have it over ride the weak default definition.

[justinbalexander]

https://zig.godbolt.org/z/GaiKrV

comptime {
    // This should be overriden by a strong definition of a symbol with the same name
    @export("func", default_func, @import("builtin").GlobalLinkage.Weak);
}

// Library supplied default version
extern fn default_func() void {
    while (true) {}
}

extern fn func() void; // declare symbol to be resolved at link time
export const vector = [](extern fn () void) {
    func,
};

// The following is in a different file outside of the package path
comptime {
    @export("func", user_func, @import("builtin").GlobalLinkage.Strong);
}

// OR (preferably) export fn func() void {
extern fn user_func() void {
    while (true) {
        // toggle a pin or something
    }
}

This is what I'm trying to do really. Am I going about this the wrong way?

Is this a separate issue?

[andrewrk]

This might be solved with #2174

[nektro]

fn square(num: i32) i32 {
    return num * num;
}
const vector = [_]usize{
    @ptrToInt(square),
};
test {
    _ = vector;
}

the following yields this error (which seems like a different fn pointer promotion bug)

test.zig:5:15: error: expected pointer, found 'fn(i32) i32'
    @ptrToInt(square),
              ^~~~~~

adding an & yields the original error and affects stage2 as well

test.zig:5:5: error: unable to evaluate comptime expression
    @ptrToInt(&square),
    ^~~~~~~~~~~~~~~~~~
test.zig:5:15: note: operation is runtime due to this operand
    @ptrToInt(&square),
              ^~~~~~~