x/sys/windows: wrong Sizeof result on struct windows.JOBOBJECT_EXTENDED_LIMIT_INFORMATION on ARCH 386

[dbellavista]

Hi! I'm trying to call the windows.SetInformationJobObject function which requires the size of the input structure of type windows.JOBOBJECT_EXTENDED_LIMIT_INFORMATION. To my understanding I can use unsafe.Sizeof to achieve the same result of the C sizeof operator.

When compiling on amd64 arch, the sizeof is correct, but on 386 there is a 4 bytes difference.

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

$ go version
go version go1.14.6 windows/amd64

Does this issue reproduce with the latest release?

Yes

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

go env Output

$ go env
set GO111MODULE=
set GOARCH=amd64
set GOBIN=
set GOCACHE=C:\Users\danie\AppData\Local\go-build
set GOENV=C:\Users\danie\AppData\Roaming\go\env
set GOEXE=.exe
set GOFLAGS=
set GOHOSTARCH=amd64
set GOHOSTOS=windows
set GOINSECURE=
set GONOPROXY=
set GONOSUMDB=
set GOOS=windows
set GOPATH=C:\Users\danie\go
set GOPRIVATE=
set GOPROXY=https://proxy.golang.org,direct
set GOROOT=c:\go
set GOSUMDB=sum.golang.org
set GOTMPDIR=
set GOTOOLDIR=c:\go\pkg\tool\windows_amd64
set GCCGO=gccgo
set AR=ar
set CC=gcc
set CXX=g++
set CGO_ENABLED=1
set GOMOD=Y:\Agent\windows-service-wrapper\go.mod
set CGO_CFLAGS=-g -O2
set CGO_CPPFLAGS=
set CGO_CXXFLAGS=-g -O2
set CGO_FFLAGS=-g -O2
set CGO_LDFLAGS=-g -O2
set PKG_CONFIG=pkg-config
set GOGCCFLAGS=-m64 -mthreads -fmessage-length=0 -fdebug-prefix-map=C:\Users\danie\AppData\Local\Temp\go-build389674314=/tmp/go-build -gno-record-gcc-switches

What did you do?

package main

// #include <windows.h>
//
// int SizeOfJob() {
//     JOBOBJECT_EXTENDED_LIMIT_INFORMATION test;
//     test.BasicLimitInformation.LimitFlags = JOB_OBJECT_LIMIT_KILL_ON_JOB_CLOSE;
//     return sizeof(test);
// }
import "C"

import (
	"fmt"
	"unsafe"

	"golang.org/x/sys/windows"
)

func main() {
	info := windows.JOBOBJECT_EXTENDED_LIMIT_INFORMATION{
		BasicLimitInformation: windows.JOBOBJECT_BASIC_LIMIT_INFORMATION{
			LimitFlags: windows.JOB_OBJECT_LIMIT_KILL_ON_JOB_CLOSE,
		},
	}

	fmt.Printf("Go Size %d\nC Size %d", unsafe.Sizeof(info), C.SizeOfJob())
}

What did you expect to see?

Compiled on windows with environment GOARCH=386

Go Size 112
C Size 112

Compiled on windows with environment GOARCH="amd64"

Go Size 144
C Size 144

What did you see instead?

Compiled on windows with environment GOARCH=386

Go Size 108
C Size 112

[networkimprov]

cc @alexbrainman

@gopherbot add OS-Windows

[cagedmantis]

/cc @ianlancetaylor @griesemer

[ianlancetaylor]

My first guess would be an alignment difference. Can you print the C offsetof and the Go unsafe.Offsetof for each field in the struct? So that we can find out exactly where the difference happens? Thanks.

[dbellavista]

@ianlancetaylor You are right. It seems to be a size difference in JOBOBJECT_BASIC_LIMIT_INFORMATION. The C size is greater (48 bytes) than the sum of the field sizes.

Offset and sizes of JOBOBJECT_EXTENDED_LIMIT_INFORMATION

Field	GO Offset	C Offset	GO Size	C Size
BasicLimitInformation	0	0	44	48
IoInfo	44	48	48	48
ProcessMemoryLimit	92	96	4	4
JobMemoryLimit	96	100	4	4
PeakProcessMemoryUsed	100	104	4	4
PeakJobMemoryUsed	104	108	4	4

Offset and sizes of JOBOBJECT_BASIC_LIMIT_INFORMATION (type of BasicLimitInformation)

Field	GO Offset	C Offset	GO Size	C Size
PerProcessUserTimeLimit	0	0	8	8
PerJobUserTimeLimit	8	8	8	8
LimitFlags	16	16	4	4
MinimumWorkingSetSize	20	20	4	4
MaximumWorkingSetSize	24	24	4	4
ActiveProcessLimit	28	28	4	4
Affinity	32	32	4	4
PriorityClass	36	36	4	4
SchedulingClass	40	40	4	4

Code

package main

// #include <windows.h>
//
// int SizeOfJob() {
//     JOBOBJECT_EXTENDED_LIMIT_INFORMATION test;
//     return sizeof(test);
// }
// int SizeOfBasicJob() {
//     JOBOBJECT_EXTENDED_LIMIT_INFORMATION test;
//     return sizeof(test.BasicLimitInformation);
// }
// int SizeOfBasicStructJob() {
//     JOBOBJECT_BASIC_LIMIT_INFORMATION test;
//     return sizeof(test);
// }
// int SizeOfBasicLimitInformation() { JOBOBJECT_EXTENDED_LIMIT_INFORMATION test; return sizeof(test.BasicLimitInformation); };
// int SizeOfIoInfo() { JOBOBJECT_EXTENDED_LIMIT_INFORMATION test; return sizeof(test.IoInfo); };
// int SizeOfProcessMemoryLimit() { JOBOBJECT_EXTENDED_LIMIT_INFORMATION test; return sizeof(test.ProcessMemoryLimit); };
// int SizeOfJobMemoryLimit() { JOBOBJECT_EXTENDED_LIMIT_INFORMATION test; return sizeof(test.JobMemoryLimit); };
// int SizeOfPeakProcessMemoryUsed() { JOBOBJECT_EXTENDED_LIMIT_INFORMATION test; return sizeof(test.PeakProcessMemoryUsed); };
// int SizeOfPeakJobMemoryUsed() { JOBOBJECT_EXTENDED_LIMIT_INFORMATION test; return sizeof(test.PeakJobMemoryUsed); };
//
// int OffsetOfBasicLimitInformation() { return offsetof(JOBOBJECT_EXTENDED_LIMIT_INFORMATION, BasicLimitInformation); };
// int OffsetOfIoInfo() { return offsetof(JOBOBJECT_EXTENDED_LIMIT_INFORMATION, IoInfo); };
// int OffsetOfProcessMemoryLimit() { return offsetof(JOBOBJECT_EXTENDED_LIMIT_INFORMATION, ProcessMemoryLimit); };
// int OffsetOfJobMemoryLimit() { return offsetof(JOBOBJECT_EXTENDED_LIMIT_INFORMATION, JobMemoryLimit); };
// int OffsetOfPeakProcessMemoryUsed() { return offsetof(JOBOBJECT_EXTENDED_LIMIT_INFORMATION, PeakProcessMemoryUsed); };
// int OffsetOfPeakJobMemoryUsed() { return offsetof(JOBOBJECT_EXTENDED_LIMIT_INFORMATION, PeakJobMemoryUsed); };
//
// int SizeOfPerProcessUserTimeLimit() { JOBOBJECT_BASIC_LIMIT_INFORMATION test; return sizeof(test.PerProcessUserTimeLimit); }
// int SizeOfPerJobUserTimeLimit() { JOBOBJECT_BASIC_LIMIT_INFORMATION test; return sizeof(test.PerJobUserTimeLimit); }
// int SizeOfLimitFlags() { JOBOBJECT_BASIC_LIMIT_INFORMATION test; return sizeof(test.LimitFlags); }
// int SizeOfMinimumWorkingSetSize() { JOBOBJECT_BASIC_LIMIT_INFORMATION test; return sizeof(test.MinimumWorkingSetSize); }
// int SizeOfMaximumWorkingSetSize() { JOBOBJECT_BASIC_LIMIT_INFORMATION test; return sizeof(test.MaximumWorkingSetSize); }
// int SizeOfActiveProcessLimit() { JOBOBJECT_BASIC_LIMIT_INFORMATION test; return sizeof(test.ActiveProcessLimit); }
// int SizeOfAffinity() { JOBOBJECT_BASIC_LIMIT_INFORMATION test; return sizeof(test.Affinity); }
// int SizeOfPriorityClass() { JOBOBJECT_BASIC_LIMIT_INFORMATION test; return sizeof(test.PriorityClass); }
// int SizeOfSchedulingClass() { JOBOBJECT_BASIC_LIMIT_INFORMATION test; return sizeof(test.SchedulingClass); }
//
// int OffsetOfPerProcessUserTimeLimit() { return offsetof(JOBOBJECT_BASIC_LIMIT_INFORMATION, PerProcessUserTimeLimit); }
// int OffsetOfPerJobUserTimeLimit() { return offsetof(JOBOBJECT_BASIC_LIMIT_INFORMATION, PerJobUserTimeLimit); }
// int OffsetOfLimitFlags() { return offsetof(JOBOBJECT_BASIC_LIMIT_INFORMATION, LimitFlags); }
// int OffsetOfMinimumWorkingSetSize() { return offsetof(JOBOBJECT_BASIC_LIMIT_INFORMATION, MinimumWorkingSetSize); }
// int OffsetOfMaximumWorkingSetSize() { return offsetof(JOBOBJECT_BASIC_LIMIT_INFORMATION, MaximumWorkingSetSize); }
// int OffsetOfActiveProcessLimit() { return offsetof(JOBOBJECT_BASIC_LIMIT_INFORMATION, ActiveProcessLimit); }
// int OffsetOfAffinity() { return offsetof(JOBOBJECT_BASIC_LIMIT_INFORMATION, Affinity); }
// int OffsetOfPriorityClass() { return offsetof(JOBOBJECT_BASIC_LIMIT_INFORMATION, PriorityClass); }
// int OffsetOfSchedulingClass() { return offsetof(JOBOBJECT_BASIC_LIMIT_INFORMATION, SchedulingClass); }
import "C"

import (
	"fmt"
	"unsafe"

	"golang.org/x/sys/windows"
)

func main() {
	info := windows.JOBOBJECT_EXTENDED_LIMIT_INFORMATION{}

	fmt.Printf("|Field | GO Offset | C Offset | GO Size | C Size|\n|-|-|-|-|-|\n")

	fmt.Printf("|BasicLimitInformation | %d | %d | %d | %d|\n", unsafe.Offsetof(info.BasicLimitInformation), C.OffsetOfBasicLimitInformation(), unsafe.Sizeof(info.BasicLimitInformation), C.SizeOfBasicLimitInformation())
	fmt.Printf("|IoInfo | %d | %d | %d | %d|\n", unsafe.Offsetof(info.IoInfo), C.OffsetOfIoInfo(), unsafe.Sizeof(info.IoInfo), C.SizeOfIoInfo())
	fmt.Printf("|ProcessMemoryLimit | %d | %d | %d | %d|\n", unsafe.Offsetof(info.ProcessMemoryLimit), C.OffsetOfProcessMemoryLimit(), unsafe.Sizeof(info.ProcessMemoryLimit), C.SizeOfProcessMemoryLimit())
	fmt.Printf("|JobMemoryLimit | %d | %d | %d | %d|\n", unsafe.Offsetof(info.JobMemoryLimit), C.OffsetOfJobMemoryLimit(), unsafe.Sizeof(info.JobMemoryLimit), C.SizeOfJobMemoryLimit())
	fmt.Printf("|PeakProcessMemoryUsed | %d | %d | %d | %d|\n", unsafe.Offsetof(info.PeakProcessMemoryUsed), C.OffsetOfPeakProcessMemoryUsed(), unsafe.Sizeof(info.PeakProcessMemoryUsed), C.SizeOfPeakProcessMemoryUsed())
	fmt.Printf("|PeakJobMemoryUsed | %d | %d | %d | %d|\n", unsafe.Offsetof(info.PeakJobMemoryUsed), C.OffsetOfPeakJobMemoryUsed(), unsafe.Sizeof(info.PeakJobMemoryUsed), C.SizeOfPeakJobMemoryUsed())

	fmt.Printf("\n")
	fmt.Printf("|Field | GO Offset | C Offset | GO Size | C Size|\n|-|-|-|-|-|\n")
	fmt.Printf("|PerProcessUserTimeLimit | %d | %d | %d | %d|\n", unsafe.Offsetof(info.BasicLimitInformation.PerProcessUserTimeLimit), C.OffsetOfPerProcessUserTimeLimit(), unsafe.Sizeof(info.BasicLimitInformation.PerProcessUserTimeLimit), C.SizeOfPerProcessUserTimeLimit())
	fmt.Printf("|PerJobUserTimeLimit | %d | %d | %d | %d|\n", unsafe.Offsetof(info.BasicLimitInformation.PerJobUserTimeLimit), C.OffsetOfPerJobUserTimeLimit(), unsafe.Sizeof(info.BasicLimitInformation.PerJobUserTimeLimit), C.SizeOfPerJobUserTimeLimit())
	fmt.Printf("|LimitFlags | %d | %d | %d | %d|\n", unsafe.Offsetof(info.BasicLimitInformation.LimitFlags), C.OffsetOfLimitFlags(), unsafe.Sizeof(info.BasicLimitInformation.LimitFlags), C.SizeOfLimitFlags())
	fmt.Printf("|MinimumWorkingSetSize | %d | %d | %d | %d|\n", unsafe.Offsetof(info.BasicLimitInformation.MinimumWorkingSetSize), C.OffsetOfMinimumWorkingSetSize(), unsafe.Sizeof(info.BasicLimitInformation.MinimumWorkingSetSize), C.SizeOfMinimumWorkingSetSize())
	fmt.Printf("|MaximumWorkingSetSize | %d | %d | %d | %d|\n", unsafe.Offsetof(info.BasicLimitInformation.MaximumWorkingSetSize), C.OffsetOfMaximumWorkingSetSize(), unsafe.Sizeof(info.BasicLimitInformation.MaximumWorkingSetSize), C.SizeOfMaximumWorkingSetSize())
	fmt.Printf("|ActiveProcessLimit | %d | %d | %d | %d|\n", unsafe.Offsetof(info.BasicLimitInformation.ActiveProcessLimit), C.OffsetOfActiveProcessLimit(), unsafe.Sizeof(info.BasicLimitInformation.ActiveProcessLimit), C.SizeOfActiveProcessLimit())
	fmt.Printf("|Affinity | %d | %d | %d | %d|\n", unsafe.Offsetof(info.BasicLimitInformation.Affinity), C.OffsetOfAffinity(), unsafe.Sizeof(info.BasicLimitInformation.Affinity), C.SizeOfAffinity())
	fmt.Printf("|PriorityClass | %d | %d | %d | %d|\n", unsafe.Offsetof(info.BasicLimitInformation.PriorityClass), C.OffsetOfPriorityClass(), unsafe.Sizeof(info.BasicLimitInformation.PriorityClass), C.SizeOfPriorityClass())
	fmt.Printf("|SchedulingClass | %d | %d | %d | %d|\n", unsafe.Offsetof(info.BasicLimitInformation.SchedulingClass), C.OffsetOfSchedulingClass(), unsafe.Sizeof(info.BasicLimitInformation.SchedulingClass), C.SizeOfSchedulingClass())
	fmt.Printf("\n")
}

[gopherbot]

Change https://golang.org/cl/251197 mentions this issue: windows: use GOARCH-specific JOBOBJECT_BASIC_LIMIT_INFORMATION

[ianlancetaylor]

@dbellavista Thanks! Looks like for Windows the alignment of JOBOBJECT_BASIC_LIMIT_INFORMATION is 8 bytes, but for Go it is 4 bytes. Sounds like we need to pad the 32-bit versions of the struct.

Can you see whether https://golang.org/cl/251197 fixes the problem? Thanks.

[dbellavista]

@ianlancetaylor thanks! The sizes are now equal

[gopherbot]

Change https://golang.org/cl/253097 mentions this issue: windows: add TestJobObjectInfo