undefined reference to `reflect.unsafe_New'

eat-swap commented 3 years ago

Hello! I have tried to compile my own project which has a dependency of "reflect2" package with the most recent gccgo but failed with a message of "undefined reference". Is it possible to make it compile using gccgo?

Details shown below:

What version of "reflect2" is used to compile?

The most recent commit (commit 333559e1834b0c1840d283d79220bf121d704022).

What version of Go are you using (`go version`)?

go version go1.16.3 gccgo (GCC) 11.0.1 20210423 (prerelease) linux/amd64

Additionally, gccgo --version tells:

gccgo (GCC) 11.0.1 20210423 (prerelease)
Copyright (C) 2021 Free Software Foundation, Inc.
This is free software; see the source for copying conditions.  There is NO
warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.

What operating system and processor architecture are you using?

$ cat /etc/issue
Arch Linux \r (\l)
$ uname -a
Linux 5.11.16-arch1-1 #1 SMP PREEMPT Wed, 21 Apr 2021 17:22:13 +0000 x86_64 GNU/Linux

What did you do?

Trying to build some code that depends on this package.

What is expected to see?

The code successfully compiles.

What you see instead?

/usr/bin/ld: /home/lam/.cache/go-build/fd/fd4891df5167b3e9b000124e5b53c9fccc0f3aa55647fda5583b97f1c087b5d9-d(_go_.o): in function `github_0com_1modern_x2dgo_1reflect2.UnsafeSliceType.UnsafeMakeSlice':
/home/lam/go/pkg/mod/github.com/modern-go/reflect2@v1.0.1/unsafe_slice.go:78: undefined reference to `reflect.unsafe_NewArray'
/usr/bin/ld: /home/lam/.cache/go-build/fd/fd4891df5167b3e9b000124e5b53c9fccc0f3aa55647fda5583b97f1c087b5d9-d(_go_.o): in function `github_0com_1modern_x2dgo_1reflect2.unsafeType.UnsafeNew':
/home/lam/go/pkg/mod/github.com/modern-go/reflect2@v1.0.1/unsafe_type.go:48: undefined reference to `reflect.unsafe_New'
/usr/bin/ld: /home/lam/go/pkg/mod/github.com/modern-go/reflect2@v1.0.1/unsafe_type.go:48: undefined reference to `reflect.unsafe_New'
/usr/bin/ld: /home/lam/go/pkg/mod/github.com/modern-go/reflect2@v1.0.1/unsafe_type.go:48: undefined reference to `reflect.unsafe_New'
/usr/bin/ld: /home/lam/go/pkg/mod/github.com/modern-go/reflect2@v1.0.1/unsafe_type.go:48: undefined reference to `reflect.unsafe_New'
/usr/bin/ld: /home/lam/go/pkg/mod/github.com/modern-go/reflect2@v1.0.1/unsafe_type.go:48: undefined reference to `reflect.unsafe_New'
/usr/bin/ld: /home/lam/.cache/go-build/fd/fd4891df5167b3e9b000124e5b53c9fccc0f3aa55647fda5583b97f1c087b5d9-d(_go_.o):/home/lam/go/pkg/mod/github.com/modern-go/reflect2@v1.0.1/unsafe_type.go:48: more undefined references to `reflect.unsafe_New' follow
collect2: error: ld returned 1 exit status

Thanks for your patient and effort.

mymedia2 commented 3 years ago

For some reason, in GCC 11 reflect.unsafe_New function was renamed to reflect.unsafe__New with two underscore. Compare:

mymedia@freesia:~$ nm -D --defined-only /usr/lib/gcc/x86_64-linux-gnu/10/libgo.so | grep 'unsafe_*New'
0000000000f05d00 T internal..z2freflectlite.unsafe_New
0000000000f05cc0 T reflect.unsafe_New
0000000000f03150 T reflect.unsafe_NewArray
mymedia@freesia:~$ nm -D --defined-only /usr/lib/gcc/x86_64-linux-gnu/11/libgo.so | grep 'unsafe_*New'
000000000100c920 T internal_1reflectlite.unsafe__New
000000000100c8e0 T reflect.unsafe__New
000000000100ca30 T reflect.unsafe__NewArray

nganhkhoa commented 2 years ago

I can verify this, and unfortunately, the problem only happens in gccgo or gollvm. Both are using a different port of libgo in gofrontend.

The mainstream go compiler: https://github.com/golang/go/blob/41b9d8c75e45636a153c2a31d117196a22a7fc6c/src/runtime/malloc.go#L1201

The libgo port for gccgo and gollvm: https://github.com/golang/gofrontend/blob/f5bc28a30b7503015bbef38afb5812313184e822/libgo/go/runtime/malloc.go#L1295

It is not clear how to fix this issue. Because go doesn't have a quick check over the defined/undefined symbols.

For people building gccgo or gollvm: It is best to make a copy of these functions and make both verions available unsafe_ and unsafe__.

For people using a distributed version of gccgo or gollvm: Fix the library call in unsafe_link.go into using unsafe__.

A related issue, if you use https://github.com/ugorji/go, fix codec/helper_unsafe.go as above.

modern-go / reflect2