Modular arithmetic fails to compile on msp430 target.

[nmichaels]

Given the following program:

const std = @import("std");

export fn modNum(a: u8) u8 {
    return a % 14;
}

fn reset() noreturn {
    asm volatile ("mov 0, r0");
    unreachable;
}

export fn main() noreturn {
    var n: u8 = 0;
    while (n < 152) : (n += 1) {
        if (modNum(n) >= 14) {
            reset();
        }
    }
    while (true) {}
}

pub export fn _start() linksection(".init9") noreturn {
    asm volatile (
        \\ jmp main
    );
    unreachable;
}

and appropriate linker scripts from TI's Energia release (or maybe MSP430-GCC, see link below), the following command ought to build something:

zig build-exe -Lldscripts -Lldscripts/msp430g2553 --script msp430.x --single-threaded -O ReleaseSmall -target msp430-freestanding-none -mcpu msp430 modulo.zig

And if you change the % in modNum to a +, it does. (Though it won't run because there's no interrupt table and _start does none of the setup stuff it's supposed to do.) However, as is, it spits out this error:

>>> referenced by modulo.zig:4 (/home/nathan/zig/mod/modulo.zig:4)
>>>               zig-cache/o/4ed470d32b8b5d645abaefc9c97f90f7/modulo.o:(modNum)
thread 1570666 panic: attempt to unwrap error: LLDReportedFailure
/home/nathan/zig/zig/lib/std/heap.zig:147:9: 0x55949f7bf986 in std.heap.CAllocator.resize (zig1)
        return error.OutOfMemory;
        ^
/home/nathan/zig/zig/lib/std/mem/Allocator.zig:319:16: 0x55949f9f3d79 in std.mem.Allocator.resize (zig1)
    const rc = try self.resizeFn(self, old_byte_slice, Slice.alignment, new_byte_count, 0, @returnAddress());
               ^
/home/nathan/zig/zig/lib/std/os.zig:1761:19: 0x55949fabf69c in std.os.unlinkatZ (zig1)
        ENOENT => return error.FileNotFound,
                  ^
/home/nathan/zig/zig/lib/std/fs.zig:1359:25: 0x55949f997a4f in std.fs.Dir.deleteFileZ (zig1)
            else => |e| return e,
                        ^
/home/nathan/zig/zig/lib/std/fs.zig:1338:13: 0x55949f905627 in std.fs.Dir.deleteFile (zig1)
            return self.deleteFileZ(&sub_path_c);
            ^
/home/nathan/zig/zig/lib/std/heap.zig:147:9: 0x55949f7bf986 in std.heap.CAllocator.resize (zig1)
        return error.OutOfMemory;
        ^
/home/nathan/zig/zig/lib/std/mem/Allocator.zig:319:16: 0x55949f9f3d79 in std.mem.Allocator.resize (zig1)
    const rc = try self.resizeFn(self, old_byte_slice, Slice.alignment, new_byte_count, 0, @returnAddress());
               ^
/home/nathan/zig/zig/lib/std/heap.zig:147:9: 0x55949f7bf986 in std.heap.CAllocator.resize (zig1)
        return error.OutOfMemory;
        ^
/home/nathan/zig/zig/lib/std/heap.zig:147:9: 0x55949f7bf986 in std.heap.CAllocator.resize (zig1)
        return error.OutOfMemory;
        ^
/home/nathan/zig/zig/lib/std/heap.zig:147:9: 0x55949f7bf986 in std.heap.CAllocator.resize (zig1)
        return error.OutOfMemory;
        ^
/home/nathan/zig/zig/lib/std/heap.zig:147:9: 0x55949f7bf986 in std.heap.CAllocator.resize (zig1)
        return error.OutOfMemory;
        ^
/home/nathan/zig/zig/lib/std/heap.zig:147:9: 0x55949f7bf986 in std.heap.CAllocator.resize (zig1)
        return error.OutOfMemory;
        ^
/home/nathan/zig/zig/lib/std/heap.zig:147:9: 0x55949f7bf986 in std.heap.CAllocator.resize (zig1)
        return error.OutOfMemory;
        ^
/home/nathan/zig/zig/lib/std/heap.zig:147:9: 0x55949f7bf986 in std.heap.CAllocator.resize (zig1)
        return error.OutOfMemory;
        ^
/home/nathan/zig/zig/lib/std/heap.zig:147:9: 0x55949f7bf986 in std.heap.CAllocator.resize (zig1)
        return error.OutOfMemory;
        ^
/home/nathan/zig/zig/lib/std/mem/Allocator.zig:319:16: 0x55949f9f3d79 in std.mem.Allocator.resize (zig1)
    const rc = try self.resizeFn(self, old_byte_slice, Slice.alignment, new_byte_count, 0, @returnAddress());
               ^
/home/nathan/zig/zig/lib/std/heap.zig:147:9: 0x55949f7bf986 in std.heap.CAllocator.resize (zig1)
        return error.OutOfMemory;
        ^
/home/nathan/zig/zig/lib/std/heap.zig:147:9: 0x55949f7bf986 in std.heap.CAllocator.resize (zig1)
        return error.OutOfMemory;
        ^
/home/nathan/zig/zig/lib/std/mem/Allocator.zig:319:16: 0x55949f9f3d79 in std.mem.Allocator.resize (zig1)
    const rc = try self.resizeFn(self, old_byte_slice, Slice.alignment, new_byte_count, 0, @returnAddress());
               ^
/home/nathan/zig/zig/lib/std/heap/arena_allocator.zig:115:13: 0x55949f88578f in std.heap.arena_allocator.ArenaAllocator.resize (zig1)
            return error.OutOfMemory;
            ^
/home/nathan/zig/zig/lib/std/mem/Allocator.zig:319:16: 0x55949f9f3d79 in std.mem.Allocator.resize (zig1)
    const rc = try self.resizeFn(self, old_byte_slice, Slice.alignment, new_byte_count, 0, @returnAddress());
               ^
/home/nathan/zig/zig/lib/std/heap.zig:147:9: 0x55949f7bf986 in std.heap.CAllocator.resize (zig1)
        return error.OutOfMemory;
        ^
/home/nathan/zig/zig/lib/std/mem/Allocator.zig:319:16: 0x55949f9f3d79 in std.mem.Allocator.resize (zig1)
    const rc = try self.resizeFn(self, old_byte_slice, Slice.alignment, new_byte_count, 0, @returnAddress());
               ^
/home/nathan/zig/zig/lib/std/heap.zig:147:9: 0x55949f7bf986 in std.heap.CAllocator.resize (zig1)
        return error.OutOfMemory;
        ^
/home/nathan/zig/zig/lib/std/mem/Allocator.zig:319:16: 0x55949f9f3d79 in std.mem.Allocator.resize (zig1)
    const rc = try self.resizeFn(self, old_byte_slice, Slice.alignment, new_byte_count, 0, @returnAddress());
               ^
/home/nathan/zig/zig/src/link/Elf.zig:1721:21: 0x55949f961ebf in link.Elf.linkWithLLD (zig1)
                    return error.LLDReportedFailure;
                    ^
/home/nathan/zig/zig/src/link/Elf.zig:733:9: 0x55949f950c16 in link.Elf.flush (zig1)
        return self.linkWithLLD(comp);
        ^
/home/nathan/zig/zig/src/link.zig:394:21: 0x55949f90cbdd in link.File.flush (zig1)
            .elf => return @fieldParentPtr(Elf, "base", base).flush(comp),
                    ^
/home/nathan/zig/zig/src/Compilation.zig:1354:5: 0x55949f905f23 in Compilation.update (zig1)
    try self.bin_file.flush(self);
    ^
/home/nathan/zig/zig/src/main.zig:1998:5: 0x55949f89ef8d in main.updateModule (zig1)
    try comp.update();
    ^
/home/nathan/zig/zig/src/main.zig:1841:21: 0x55949f7ece18 in main.buildOutputType (zig1)
        else => |e| return e,
                    ^
/home/nathan/zig/zig/src/main.zig:162:9: 0x55949f7c3e25 in main.mainArgs (zig1)
        return buildOutputType(gpa, arena, args, .{ .build = .Exe });
        ^
???:?:?: 0x55949f7c5245 in ??? (???)
/home/nathan/zig/zig/src/stage1.zig:45:43: 0x55949f7c396d in main (zig1)
        stage2.mainArgs(gpa, arena, args) catch unreachable;
                                          ^
Aborted

I zipped up a copy of this source and the linker scripts and put it at:

https://www.nmichaels.org/files/modbug.tar.gz

It seems like __mspabi_remu is being emitted by the compiler, but it's missing from the runtime library. While we're at it, there's a large set of functions like this that ought to be in compiler-rt documented in the ABI.

LLVM's implementation:
https://github.com/llvm/llvm-project/blob/d480f968ad8b56d3ee4a6b6df5532d485b0ad01e/llvm/test/CodeGen/MSP430/libcalls.ll