cmd/go: go test -compiler gccgo produces duplicate symbol errors

[davecheney]

What steps will reproduce the problem?

See attached zip file for reproduction

What is the expected output? What do you see instead?

This sample passes with -compiler gc

 % go test -compiler gc -v  issue/...
=== RUN TestData
--- PASS: TestData (0.00 seconds)
        a_test.go:6: 0 false 
=== RUN TestXData
--- PASS: TestXData (0.00 seconds)
        x_test.go:7: foo &{0 false }
PASS
ok      issue/a 0.005s
?       issue/b [no test files]

But blows up due to duplicate symbols during linking of a/a.test

ucky(~/src) % go test -compiler gccgo -v  issue/...
# testmain
/tmp/go-build896181789/issue/a/_test/issue/liba.a(a.o):(.rodata.__go_tdn_issue_a..issue_a.t+0x0):
multiple definition of `__go_tdn_issue_a..issue_a.t'
/tmp/go-build896181789/issue/liba.a(a.o):(.rodata.__go_tdn_issue_a..issue_a.t+0x0):
first defined here
/tmp/go-build896181789/issue/a/_test/issue/liba.a(a.o): In function `issue_a.TestData':
/home/dfc/src/issue/a/a_test.go:5: multiple definition of `issue_a.Data'
/tmp/go-build896181789/issue/liba.a(a.o):(.bss+0x0): first defined here
/tmp/go-build896181789/issue/a/_test/issue/liba.a(a.o): In function `issue_a..import':
/home/dfc/src/issue/a/a.go:1: multiple definition of `issue_a..import'
/tmp/go-build896181789/issue/liba.a(a.o):/home/dfc/src/issue/a/a.go:1: first defined here
collect2: error: ld returned 1 exit status
FAIL    issue/a [build failed]
?       issue/b [no test files]

Please use labels and text to provide additional information.

Looking at the -x output for go test issue/a

gccgo -o $WORK/issue/a/_test/a.test $WORK/issue/a/_test/main.o -Wl,-( -m64
$WORK/issue/a/_test/issue/liba_test.a $WORK/issue/libb.a $WORK/issue/liba.a
$WORK/issue/a/_test/issue/liba.a -Wl,-)

liba.a is present twice, once in it's normal form, and once in it's extended (due to the
export_test.go) form. 

I am guessing that the first liba.a leaks in due to the transitive import via issue/b.

Attachments:

1. issue.tar.gz (487 bytes)

[ianlancetaylor]

Comment 1:

My understanding is that this is repo-main because that is where cmd/go lives.
I guess we don't currently have a tag for gccgo-specific changes to the main repo.

Labels changed: added repo-main, gccgo, removed repo-gccgo.

[davecheney]

Comment 2:

Here is what I *think* is happening,
Under -compiler gc, the _test.go files are combined with the normal files for the
package under test and placed into a .a file in $WORK, then everything is linked together
/home/dfc/go/pkg/tool/linux_amd64/6l -o $WORK/issue/a/_test/a.test -L
$WORK/issue/a/_test -L $WORK -L /home/dfc/pkg/linux_amd64 -w -extld=clang
$WORK/issue/a/_test/main.a
$WORK/issue/a/_test/a.test
you can see that -L $WORK/issue/a/_test comes before -L $WORK so all the symbols for
issue/a will be taken from the temporary test .a file in $WORK/issue/a/_test.
But, under -compiler gccgo we see
gccgo -o $WORK/issue/a/_test/a.test $WORK/issue/a/_test/main.o -Wl,-( -m64
$WORK/issue/a/_test/issue/liba_test.a $WORK/issue/libb.a $WORK/issue/liba.a
$WORK/issue/a/_test/issue/liba.a -Wl,-)
specifically $WORK/issue/liba.a appears before $WORK/issue/a/_test/issue/liba.a so the
linker lodas issue/liba.a but can't find all the symbols it needs, so falls through to
_test/issue/liba.a which has the additional test related symbols, but also has symbols
that were previously discovered in the previous liba.a.
This is all just speculation, I don't know how /usr/bin/ld does it's symbol resolution,
but it would make sense to defer opening a library until it's know that none of the
previous libraries had all the symbols you needed.
The solution would appear to be, make sure that _test/issue/liba.a comes first in the
linking order as it does with -compiler gc

[davecheney]

Comment 3:

Unassigned from myself, if anyone else wants to take a crack, go for it.

Owner changed to ---.

[davecheney]

Comment 4:

https://golang.org/cl/80300043/

Owner changed to @davecheney.

Status changed to Started.

[davecheney]

Comment 5:

This issue was closed by revision 3ce1677.

Status changed to Fixed.