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xbt573 opened this issue Nov 12, 2024 · 3 comments
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x/sys/unix, syscall: incorrect return value as output parameter on s390x Big Endian #70302

xbt573 opened this issue Nov 12, 2024 · 3 comments
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arch-s390x Issues solely affecting the s390x architecture. compiler/runtime Issues related to the Go compiler and/or runtime.
Milestone
Unreleased

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@xbt573
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xbt573 commented Nov 12, 2024 •
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Go version

go version go1.23.2 linux/s390x

Output of go env in your module/workspace:

GO111MODULE=''
GOARCH='s390x'
GOBIN=''
GOCACHE='/home/xbt573/.cache/go-build'
GOENV='/home/xbt573/.config/go/env'
GOEXE=''
GOEXPERIMENT=''
GOFLAGS=''
GOHOSTARCH='s390x'
GOHOSTOS='linux'
GOINSECURE=''
GOMODCACHE='/home/xbt573/go/pkg/mod'
GONOPROXY=''
GONOSUMDB=''
GOOS='linux'
GOPATH='/home/xbt573/go'
GOPRIVATE=''
GOPROXY='direct'
GOROOT='/usr/lib/golang'
GOSUMDB='off'
GOTMPDIR=''
GOTOOLCHAIN='local'
GOTOOLDIR='/usr/lib/golang/pkg/tool/linux_s390x'
GOVCS=''
GOVERSION='go1.23.2'
GODEBUG=''
GOTELEMETRY='local'
GOTELEMETRYDIR='/home/xbt573/.config/go/telemetry'
GCCGO='gccgo'
AR='ar'
CC='gcc'
CXX='g++'
CGO_ENABLED='1'
GOMOD='/dev/null'
GOWORK=''
CGO_CFLAGS='-O2 -g'
CGO_CPPFLAGS=''
CGO_CXXFLAGS='-O2 -g'
CGO_FFLAGS='-O2 -g'
CGO_LDFLAGS='-O2 -g'
PKG_CONFIG='pkg-config'
GOGCCFLAGS='-fPIC -m64 -march=z196 -pthread -Wl,--no-gc-sections -fmessage-length=0 -ffile-prefix-map=/tmp/go-build1678900633=/tmp/go-build -gno-record-gcc-switches'

What did you do?

package main

import (
        "os"
        "fmt"
        "syscall"
        "unsafe"
        "golang.org/x/sys/unix"
)

func main() {
        f, err := os.Open(os.Args[1])
        if err != nil {
                panic(err)
        }
        defer f.Close()

        var attr int

        _, _, rerr := unix.Syscall(syscall.SYS_IOCTL, f.Fd(), uintptr(unix.FS_IOC_GETFLAGS), uintptr(unsafe.Pointer(&attr)))
        if rerr != 0 {
                panic(rerr)
        }

        fmt.Println(attr)
}
$ ./playground /path/to/file/

C equivalent if you want to test it on the same machine:

#include <stdio.h>
#include <sys/stat.h>
#include <sys/ioctl.h>
#include <fcntl.h>
#include <unistd.h>

#include <linux/fs.h>

int main(int argc, char **argv) {
        int fd, r, f;

        fd = open(argv[1], O_RDONLY|O_NONBLOCK|O_NOFOLLOW);
        if (fd == -1) {
                return 1;
        }
        r = ioctl(fd, FS_IOC_GETFLAGS, &f);
        if (r == -1) {
                return 2;
        }

        printf("%d\n", f);

        close(fd);

}

What did you see happen?

This program returns 549755813888 for file, which flags supposed to be 128, almost identical C program also returns 128 as it is expected. Note that 128 << 32 == 549755813888. I think this bug is caused by big-endianness of s390x architecture.

What did you expect to see?

I expected to see correct return value from output parameter (number 128).

Example file with the same flags (128) can be created with following commands

$ touch example
# chattr +A example
@gopherbot gopherbot added the compiler/runtime Issues related to the Go compiler and/or runtime. label Nov 12, 2024
@gabyhelp
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Related Issues

(Emoji vote if this was helpful or unhelpful; more detailed feedback welcome in this discussion.)

@xbt573
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xbt573 commented Nov 12, 2024 •
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I suppose use of IoctlGetUint32 is not always safe because FS_IOC_GETFLAGS is limited to C long, which can (but can not) be bigger than uint32.

https://github.com/torvalds/linux/blob/master/include/uapi/linux/fs.h#L223

@seankhliao seankhliao changed the title golang.org/x/sys/unix, syscall: Incorrect return value as output parameter on Big Endian x/sys/unix, syscall: incorrect return value as output parameter on s390x Big Endian Nov 12, 2024
@seankhliao seankhliao added the arch-s390x Issues solely affecting the s390x architecture. label Nov 12, 2024
@gopherbot gopherbot added this to the Unreleased milestone Nov 12, 2024
@ianlancetaylor
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The C type int is normally 32 bits. On s390x the Go type int is 64 bits. You can't pass a pointer to a Go int to a system call that is expecting a pointer to a C int. Normally when calling a syscall that expects a pointer to the C type int, you should pass a pointer to the Go type int32.

Closing because there is nothing to change in the Go project.

@ianlancetaylor ianlancetaylor closed this as not planned Won't fix, can't repro, duplicate, stale Nov 12, 2024
@xbt573 xbt573 mentioned this issue Nov 12, 2024
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@ianlancetaylor @gopherbot @seankhliao @xbt573 @gabyhelp