[MachO] error: unsupported linker arg: -no_pie

[motiejus]

Currently we cannot compile CGo programs to MacOS (at least x86_64) with default settings. Example Go file:

main.go

package main

// #include <stdio.h>
// char* hello() { return "hello, world"; }
// void phello() { printf("%s\n", hello()); }
import "C"

func main() {
        C.phello()
}

func Chello() string {
        return C.GoString(C.hello())
}

Compile to MacOS

$ CGO_ENABLED=1 GOOS=darwin GOARCH=amd64 CC="zig cc -target x86_64-macos-none" go build  .
# example.com/x
/usr/local/go/pkg/tool/linux_amd64/link: running zig failed: exit status 1
error: unsupported linker arg: -no_pie

[motiejus]

Related: #15439

[kubkon]

I don't think we ever wanted to enable non PIE builds on macOS mainly because it is x86_64 specific. Thoughts?

[motiejus]

I don't think we ever wanted to enable non PIE builds on macOS mainly because it is x86_64 specific. Thoughts?

I personally don't care much about it nor truly understand the impact on this flag.

I am reporting the issue, because Go just adds it on x86_64. We need some way to make Go compile the CGo binaries for x86_64-macos.

Here is the CR in Go that added it: https://go-review.googlesource.com/c/go/+/201358

Or do we really need it? x86_64-macos is on the verge of being abandoned by Apple altogether.

[kubkon]

This flag is required to disambiguate position-dependent from position-independent code models generated by the compiler. The linker has no idea which model it should assume which is important to correctly apply relocations and relaxations. x86_64-macos allows both position-dependent and -independent models while aarch64-macos is strictly position-independent. Zig currently always assumes position-independent code (PIE) for macOS targets, while Go by default uses position-dependent code model for x86_64-macos (non-PIE), and position-independent for aarch64-macos (PIE).

If Apple is on the verge of discontinuing x86_64-macos and given we only support the latest 3 macOS releases, I think we have the luxury to put this feature in our good-to-have list of features that we might work on in the distant future.

[matklad]

Hit "zig cc doesn't work as CC for cgo on Mac" at TigerBeetle. Would work around, as that's not critical, but having this just work would be nice!

[alexrp]

Does CGo actually require position-dependent code?

In any case, for Clang-level arguments, we currently handle -no-pie (and its many variations) by setting create_module.opts.pie = false. This ultimately goes ignored when linking on macOS. It seems to me that handling the -no_pie linker option in the same way would at least be no worse than that. And if CGo doesn't actually care about PIE, it would unblock this scenario. @kubkon thoughts?

[kubkon]

Does CGo actually require position-dependent code?

In any case, for Clang-level arguments, we currently handle -no-pie (and its many variations) by setting create_module.opts.pie = false. This ultimately goes ignored when linking on macOS. It seems to me that handling the -no_pie linker option in the same way would at least be no worse than that. And if CGo doesn't actually care about PIE, it would unblock this scenario. @kubkon thoughts?

There's way more than just forwarding a flag to the linker. We are actually missing all of non-pic/pie handling in the linker, so no, it's not a simple change.

[alexrp]

I think you misunderstood my comment? I'm acknowledging exactly that.

[alexrp]

What I'm saying is: We already handle the Clang-level (no-)PIE flags by setting create_module.opts.pie, but as you say, they're not respected by the Mach-O linker at the end of the day. But you can at least build with the flags without getting an error; you just won't get position-dependent output.

So I'm suggesting that we can just do the same for the -no_pie linker-level option: Accept it and do the same thing, with the understanding that actually emitting position-dependent output in the linker is a TODO.

[alexrp]

As an aside, @motiejus @matklad some searching suggests that you can use something like GOFLAGS="-buildmode=pie" to prevent that flag being emitted in the first place.

[am11]

The dotnet AOT toolchain uses these related lld/bfd flags: -pie, -no-pie and -static-pie (depending on higher-level msbuild flags). Perhaps those could also be handled by zig as part of this request (to avoid workarounds like these: https://github.com/MichalStrehovsky/PublishAotCross/blob/45d90a19c46ba2ce7fd6158babb045d665a678a2/src/clang.cmd#L19).

[alexrp]

@am11 I've included dd93cf9 in #20384. But please note that all this does is wire it up in the frontend; it depends on the linker backend (lld vs zld) whether it's actually respected.

I'll do a follow-up PR after #20384 to add the linker flags that are being removed in that clang.cmd.

[kubkon]

Please note this issue is low priority for me especially since Apple ditched x86_64 and aarch64 doesn't support this flag anyhow.