cmd/6l: -shared generated invalid relocations

[mwhudson]

I guess this falls into the category of things not really guaranteed to work, but:

mwhudson@narsil:shared-lib-stuff$ cat trivialmain.go 
package main

func main () {}
mwhudson@narsil:shared-lib-stuff$ go build -ldflags -shared trivialmain.go
# command-line-arguments
/usr/bin/ld: /var/tmp/go-link-teMwJN/go.o: relocation R_X86_64_TPOFF32 against `runtime.tlsg' can not be used when making a shared object; recompile with -fPIC
/var/tmp/go-link-teMwJN/go.o: error adding symbols: Bad value
collect2: error: ld returned 1 exit status
/opt/opensource/go/pkg/tool/linux_amd64/6l: running gcc failed: unsuccessful exit status 0x100

I think this was broken by 90093f0. For ARM the roughly analogous change (b377c9c) was fixed by 9ed5995.

[minux]

I don't think -shared is supported except for linux/arm....

[mwhudson]

Well yes, but I'm working on shared libraries for go and so I need this sort of thing to work :) I don't expect anyone else to fix it.

[mwhudson]

mwhudson/go@master...5391ba7 sort of fixes this, as well as being terrible in a variety of ways.

[spetrovic77]

Is the command in the issue description supposed to work as is? I'm still getting the same error as in the description on amd64 linux.

[mwhudson]

Unfortunately I bungled a rebase and dropped part of the change; see https://go-review.googlesource.com/#/c/6802/

Even then you need to pass -shared to the compiler and assembler as well as the linker.

[spetrovic77]

Okay, I'm indeed able to build with -shared passed to all the commands, with your new patch.

Btw., how are you passing -shared to the assembler? I've had to add -asmflags to the go/build command and pass that along.

[mwhudson]

Same! https://go-review.googlesource.com/#/c/4280/

Eventually I'll add the flags from the "Execution Modes" doc by @ianlancetaylor I hope.