race: 'unsupported VMA range' on linux/arm64

[mengzhuo]

I think it might related to
https://github.com/llvm-mirror/compiler-rt/blob/master/lib/dfsan/dfsan.cc#L85

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

master

$ go version devel +8c10ce164f Fri Jan 25 15:16:56 2019 +0000 linux/arm64

Does this issue reproduce with the latest release?

No

go test -v -race
go test: -race is only supported on linux/amd64, linux/ppc64le, freebsd/amd64, netbsd/amd64, darwin/amd64 and windows/amd64

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

Linux/arm64
CPU: RockChip 3399pro

go env Output

$ uname -a
Linux RK3399 4.4.167 #17 SMP Sat Jan 19 14:04:40 CST 2019 aarch64 aarch64 aarch64 GNU/Linux
$ go env

GOARCH="arm64"

GOBIN=""

GOCACHE="/root/.cache/go-build"

GOEXE=""

GOFLAGS=""

GOHOSTARCH="arm64"

GOHOSTOS="linux"

GOOS="linux"

GOPATH="/root/go"

GOPROXY=""

GORACE=""

GOROOT="/usr/local/go"

GOTMPDIR=""

GOTOOLDIR="/usr/local/go/pkg/tool/linux_arm64"

GCCGO="gccgo"

CC="gcc"

CXX="g++"

CGO_ENABLED="1"

GOMOD=""

CGO_CFLAGS="-g -O2"

CGO_CPPFLAGS=""

CGO_CXXFLAGS="-g -O2"

CGO_FFLAGS="-g -O2"

CGO_LDFLAGS="-g -O2"

PKG_CONFIG="pkg-config"

GOGCCFLAGS="-fPIC -pthread -fmessage-length=0 -fdebug-prefix-map=/tmp/go-build737658841=/tmp/go-build -gno-record-gcc-switches"

What did you do?

What did you expect to see?

ALL test passed.

What did you see instead?

## all non-race test passed

./all.bash -v
......
##### os/user with tag osusergo
ok      os/user 0.010s

##### GOMAXPROCS=2 runtime -cpu=1,2,4 -quick
ok      runtime 29.164s

##### cmd/go terminal test
PASS
ok      _/root/godev/src/cmd/go/testdata/testterminal18153      0.007s

##### sync -cpu=10
ok      sync    2.018s

##### Testing race detector
FATAL: ThreadSanitizer: unsupported VMA range
FATAL: Found 39 - Supported 48
FAIL    runtime/race    0.035s
2019/01/27 22:55:33 Failed: exit status 1
FATAL: ThreadSanitizer: unsupported VMA range
FATAL: Found 39 - Supported 48
FAIL    flag    0.041s
FATAL: ThreadSanitizer: unsupported VMA range
FATAL: Found 39 - Supported 48
FAIL    net     0.012s
FATAL: ThreadSanitizer: unsupported VMA range
FATAL: Found 39 - Supported 48
FAIL    os      0.015s
FATAL: ThreadSanitizer: unsupported VMA range
FATAL: Found 39 - Supported 48
FAIL    os/exec 0.009s
FATAL: ThreadSanitizer: unsupported VMA range
FATAL: Found 39 - Supported 48
FAIL    encoding/gob    0.012s
2019/01/27 22:55:37 Failed: exit status 1
FATAL: ThreadSanitizer: unsupported VMA range
FATAL: Found 39 - Supported 48
exit status 66
FAIL    _/root/godev/misc/cgo/test      0.007s
2019/01/27 22:56:00 Failed: exit status 1
FATAL: ThreadSanitizer: unsupported VMA range
FATAL: Found 39 - Supported 48
FAIL    flag    0.013s
FATAL: ThreadSanitizer: unsupported VMA range
FATAL: Found 39 - Supported 48
FAIL    os/exec 0.016s
2019/01/27 22:56:01 Failed: exit status 1

##### ../misc/cgo/stdio
skipped due to earlier error

##### ../misc/cgo/life
skipped due to earlier error

##### ../misc/cgo/test
skipped due to earlier error

##### ../misc/cgo/testgodefs
skipped due to earlier error
2019/01/27 22:56:07 FAILED

[mengzhuo]

#25682

It seems to be intensional not to support VMA 39 https://reviews.llvm.org/D52167

[mengzhuo]

@dvyukov @cherrymui @zorrorffm

[Zheng-Xu]

@mengzhuo Your observation is correct. It is a combined problem with Golang and compiler-rt. 39-bit VMA cannot easily be supported by TSAN for Go heap in compiler-rt. Actually there is also some problems with 42-bit VMA. TSAN runtime requires GO heap to be in the range [0x00c000000000, 0x00e000000000], a part of shadow memory region will be out of 42bits address(See: https://github.com/llvm-mirror/compiler-rt/blob/58d43607862096aeb32d72173911c9df244a30f1/lib/tsan/rtl/tsan_platform.h#L795). In theory, we should be able to support 47-bit VMA. But it is not a common configuration in Linux distos, so only 48-bit VMA is supported.

[cherrymui]

Thanks @mengzhuo and @Zheng-Xu for the investigation.

What is the right solution here? Reconfigure the kernel to use 48-bit VMA? Is there anything we can do on the Go side?

[Zheng-Xu]

On the Go side, it is better that we ignore the tests on arm64 when the kernel is not configured as 48-bit VMA.

[cherrymui]

Thanks, @Zheng-Xu. How do we check that? Reading kernel config? Or we can just try to map some address and see if it works? Mind contributing a CL? Thanks.

We should probably also document this in the release note.

[Zheng-Xu]

@cherrymui I took a quick look on disabling the test. But I don't have a good solution so far. I try to list what I found and the difficulty here:

• Check VM bits
  1. Reading kernel config can be difficult in some cases. Exporting kernel config is an optional feature.
  2. Mapping some addresses may also be unreliable due to unknown memory layout during the execution.
  3. llvm/compiler-rt get VMA size by checking the most significant bit of the stack. https://github.com/llvm-mirror/compiler-rt/blob/58d43607862096aeb32d72173911c9df244a30f1/lib/tsan/rtl/tsan_platform_linux.cc#L212
• runtime check
  1. Only g0 stack of the main thread is allocated by kernel. It is almost impossible to get VMA size by normal Go application. We will have to add some new interface in runtime to return VMA size.
• existing checks for race detector support
  1. build time check. All other architectures either support race detector or doesn't support. So they can do build time check: https://go.googlesource.com/go/+/master/src/cmd/go/internal/work/init.go#51 and https://go.googlesource.com/go/+/master/src/cmd/internal/sys/supported.go#9
  2. dist/test will enable race detector if race detector is supported. https://go.googlesource.com/go/+/master/src/cmd/dist/test.go#1335 and https://go.googlesource.com/go/+/master/src/cmd/dist/test.go#1474
  3. I don't have a good solution to check VMA size in dist/test because cmd/dist has to be buildable by Go 1.4. And I didn't have an easy way to check VMA size, except adding some new interface in runtime.
• Possible solution
  1. no build time check for arm64. We are always able to build with race. This is reasonable, because it can be cross-compiled.
  2. execution will fail if the binary is build with race and kernel is not configured to use 48-bit VMA.
  3. Always disable "-race" for arm64 in https://go.googlesource.com/go/+/master/src/cmd/dist/test.go#1474

Do you think above solution is reasonable? I can push a CL if it is OK.

[cherrymui]

Thanks for the information.

As you said, we should not do anything at build time, exactly because of cross compilation.

Always disabling -race test in cmd/dist is also not a good idea, as we'll not know if it breaks.

Maybe in cmd/dist, we can check the stderr and if it is the unsupported VMA failure, we turn it into SKIP instead of FAIL?

Users who use the race detector can still encounter this in their own programs. So we still need to document this.

[gopherbot]

Change https://golang.org/cl/160919 mentions this issue: cmd/dist: skip race detector test failure for unsupported VMA

[zorrorffm]

@cherrymui Could you mind take a look the patch catching unsupported VMA failure and skipping that.

[ianlancetaylor]

If I understand this correctly, the race detector simply doesn't work reliably on arm64 systems. And the problem can only be fixed in race.syso, not in Go code.

That's too bad, but I think that for 1.12 we should remove arm64 from raceDetectorSupported in cmd/dist/test.go and cmd/internal/sys/supported.go. It wasn't supported in 1.11, so this is not a regression. We can try again to enable it in 1.13.