syscall, runtime: New ABI separation breaks //go:linkname

[Helflym]

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

go version devel +e092e96d4e Tue Nov 13 13:47:34 2018 -0600 aix/ppc64
after 685aca4 + few AIX commits not yet pushed.

Does this issue reproduce with the latest release?

No

What operating system and processor architecture are you using (go env)?

aix/ppc64

What did you do?

The new ABI separation seems to break relocations linked with some //go:linkname between syscall functions and their runtime implementation:

root@castor4:/opt/freeware/src/packages/BUILD/go-build/src(cgo)$ ./make.bash 
Building Go cmd/dist using /opt/freeware/lib/golang.
Building Go toolchain1 using /opt/freeware/lib/golang.
Building Go bootstrap cmd/go (go_bootstrap) using Go toolchain1.
Building Go toolchain2 using go_bootstrap and Go toolchain1.
# cmd/link
internal/syscall/unix.syscall6: relocation target syscall.syscall6 not defined for ABI0 (but is defined for ABIInternal)
go tool dist: FAILED: /opt/freeware/src/packages/BUILD/go-build/pkg/tool/aix_ppc64/go_bootstrap install -gcflags=all= -ldflags=all= -i cmd/asm cmd/cgo cmd/compile cmd/link: exit status 2

Here is what triggers the fault:
internal/syscall/unix/asm_aix_ppc64.s:

TEXT ·syscall6(SB),NOSPLIT,$0
	JMP	syscall·syscall6(SB)

syscall/syscall_aix.go:

// Implemented in runtime/syscall_aix.go.
func rawSyscall6(trap, nargs, a1, a2, a3, a4, a5, a6 uintptr) (r1, r2 uintptr, err Errno)
func syscall6(trap, nargs, a1, a2, a3, a4, a5, a6 uintptr) (r1, r2 uintptr, err Errno)

runtime/syscall_aix.go:

//go:linkname syscall_syscall6 syscall.syscall6
func syscall_syscall6(fn, nargs, a1, a2, a3, a4, a5, a6 uintptr) (r1, r2, err uintptr) { ... }
//go:linkname syscall_rawSyscall6 syscall.rawSyscall6
func syscall_rawSyscall6(fn, nargs, a1, a2, a3, a4, a5, a6 uintptr) (r1, r2, err uintptr) { ... }

Note that creating a JMP in syscall/asm_aix_ppc64.s instead of a //go:linkname fixes it:

TEXT ·syscall6(SB),NOSPLIT,$0
	JMP	runtime·syscall_syscall6(SB)

Is it indented to avoid ABI bypass or something like this ? Or just a bug ?

@aclements

[aclements]

Ah, sorry I missed internal/syscall. We probably just need to add that to the list of known cross-package references in cmd/go. I'll send a patch in a little bit.

[aclements]

@Helflym, could you try this patch? If this works, I'll mail a CL. Thanks!

diff --git a/src/cmd/go/internal/work/gc.go b/src/cmd/go/internal/work/gc.go
index 89ef2da8cb..a360a1f620 100644
--- a/src/cmd/go/internal/work/gc.go
+++ b/src/cmd/go/internal/work/gc.go
@@ -297,7 +297,7 @@ func (gcToolchain) symabis(b *Builder, a *Action, sfiles []string) (string, erro
        if p.ImportPath == "runtime" {
                // Assembly in syscall and runtime/cgo references
                // symbols in runtime.
-               otherPkgs = []string{"syscall", "runtime/cgo"}
+               otherPkgs = []string{"syscall", "internal/syscall", "runtime/cgo"}
        } else if p.ImportPath == "runtime/internal/atomic" {
                // sync/atomic is an assembly wrapper around
                // runtime/internal/atomic.

[Helflym]

It needs to be "internal/syscall/unix". Otherwise, it doesn't work.

[gopherbot]

Change https://golang.org/cl/149817 mentions this issue: cmd/go: more cross-package references from internal/syscall/unix

[Helflym]

@aclements I've the same problem with x/sys/unix which has a jmp to syscall.rawSyscall6.

# golang.org/x/sys/unix.test
golang.org/x/sys/unix.rawSyscall6: relocation target syscall.rawSyscall6 not defined for ABI0 (but is defined for ABIInternal)
FAIL    golang.org/x/sys/unix [build failed]

Do you want to add it as another cross-package ? Or do I need to remove the linkname which will remove further problems like this one ?

Edit: I've submitted https://go-review.googlesource.com/c/go/+/153997 which should remove definitely this issue, as syscall.Syscall6 might be called from any packages.

[gopherbot]

Change https://golang.org/cl/153997 mentions this issue: syscall: remove linknames to runtime symbols for aix/ppc64