x/sys/unix: go get -u -linkshared -buildmode=shared golang.org/x/sys/unix results in error: call to `syscall.Syscall' lacks nop, can't restore toc; recompile with -fPIC

[laboger]

Please answer these questions before submitting your issue. Thanks!

1. What version of Go are you using (go version)?
   go version devel +ff37d0e Tue Aug 9 17:13:43 2016 +0000 linux/ppc64le
2. What operating system and processor architecture are you using (go env)?
   ppc64le Ubuntu 16.04
3. What did you do?
   If possible, provide a recipe for reproducing the error.
   A complete runnable program is good.
   A link on play.golang.org is best.
   Set up a directory and set the GOPATH to it.
   go install -buildmode=shared std
   go get -u -linkshared -buildmode=shared golang.org/x/sys/unix
4. What did you expect to see?
   No output, correct shared library built for golang.org/x/sys/unix.
5. What did you see instead?
   go get -u -linkshared -buildmode=shared golang.org/x/sys/unix
   //# /tmp/go-build737614428/libgolang.org-x-sys-unix.so
   /home/boger/golang/upstream/go/pkg/tool/linux_ppc64le/link: running gcc failed: exit status 1
   /usr/bin/ld: /tmp/go-link-742945850/go.o: In function local.golang.org/x/sys/unix.Syscall': go.go:(.text+0x1b4c8): call tosyscall.Syscall' lacks nop, can't restore toc; recompile with -fPIC
   /usr/bin/ld: go.go:(.text+0x1b4c8): unresolvable R_PPC64_REL24 against syscall.Syscall' /usr/bin/ld: /tmp/go-link-742945850/go.o: In functionlocal.golang.org/x/sys/unix.Syscall6':
   go.go:(.text+0x1b4d8): call to syscall.Syscall6' lacks nop, can't restore toc; recompile with -fPIC /usr/bin/ld: go.go:(.text+0x1b4d8): unresolvable R_PPC64_REL24 againstsyscall.Syscall6'
   /usr/bin/ld: /tmp/go-link-742945850/go.o: In function local.golang.org/x/sys/unix.RawSyscall': go.go:(.text+0x1b4e8): call tosyscall.RawSyscall' lacks nop, can't restore toc; recompile with -fPIC
   /usr/bin/ld: go.go:(.text+0x1b4e8): unresolvable R_PPC64_REL24 against syscall.RawSyscall' /usr/bin/ld: /tmp/go-link-742945850/go.o: In functionlocal.golang.org/x/sys/unix.RawSyscall6':
   go.go:(.text+0x1b4f8): call to syscall.RawSyscall6' lacks nop, can't restore toc; recompile with -fPIC /usr/bin/ld: go.go:(.text+0x1b4f8): unresolvable R_PPC64_REL24 againstsyscall.RawSyscall6'
   /usr/bin/ld: final link failed: Bad value
   collect2: error: ld returned 1 exit status

[mwhudson]

Some BRs need to become BLs I bet.

[laboger]

Hmm thought I tried that a few weeks ago and it didn't work, but now it does. I'll create a fix for it.

[laboger]

I think there might be a problem with doing that, because the code in zsyscall_linux_ppc64le.go needs the LR to be correct, and if I change the BRs to BLs in asm_linux_ppc64x.s then the link register would have to be saved and restored in the asm, which would be unnecessary and bad for performance.
In looking further, I don't understand why zsyscall_linux_ppc64le.go has to call the syscall functions in asm_linux_ppc64x.s which then does a BR to the syscall.Syscall (or syscall.Syscall6, or syscall.RawSyscall, etc.). Couldn't the asm file be avoid altogether and just call syscall.Syscall directly from zsyscall_linux_ppc64le.go?

[gopherbot]

Change https://golang.org/cl/146518 mentions this issue: unix: fix errors in syscalls when using -linkshared