syscall, x/sys/unix: Time(), Utime(), Getrlimit() use invalid syscall number on linux/arm

[hirochachacha]

Please answer these questions before submitting your issue. Thanks!

1. What version of Go are you using (go version)?
   any
2. What operating system and processor architecture are you using (go env)?
   linux/arm
3. What did you do?
   (Use play.golang.org to provide a runnable example, if possible.)
   nothing
4. What did you expect to see?
   invalid syscall numbers are not used
5. What did you see instead?
   invalid syscall numbers are used

As far as is known, linux/arm sycalls are slightly limited.
Here is the list taken from kernel header:

/*
 * The following syscalls are obsolete and no longer available for EABI.
 */
#if !defined(__KERNEL__)
#if defined(__ARM_EABI__)
#undef __NR_time
#undef __NR_umount
#undef __NR_stime
#undef __NR_alarm
#undef __NR_utime
#undef __NR_getrlimit
#undef __NR_select
#undef __NR_readdir
#undef __NR_mmap
#undef __NR_socketcall
#undef __NR_syscall
#undef __NR_ipc
#endif
#endif

I confirmed time, utime and getrlimit are used, others are not used in both syscall package and x/sys/unix package.

I also suggest such syscall numbers should be removed from these packages on linux/arm.
(except syscall package? because of compatibility promise)

Thank you.

[bradfitz]

Please show a complete program which misbehaves, and the strace -f ./yourbinary output when run on linux/arm. Thanks.

[hirochachacha]

Actually, I found this by just reading source code. I have no accessible linux/arm here.
You are right. I should have tried it before filing as a issue. Sorry.
I'll try it later by QEMU or something. Thank you for your reply.

[hirochachacha]

Input:

package main

import (
    "syscall"
)
func main() {
    t := new(syscall.Time_t)

    _, err := syscall.Time(t)
    if err != nil {
        println(err.Error())
    }
}

Output:

function not implemented

As I expected, linux return ENOSYS. is it enough info?

[hirochachacha]

For the record, root of the problem is code-generation scripts couldn't recognize #undef.
We should fix such scripts and hope nothing changes after re-generation.

[davecheney]

@hirochachacha the syscall package is a mismash of incompatible implementations. The go runtime does not use syscall.Time, it uses an implementation of nanotime(2), although that depends on the platform you are calling it on.

If there is a fix that needs to be made, it will be in the x/sys/unix package, the syscall package is closed for modifications.

[hirochachacha]

the syscall package is a mismash of incompatible implementations. The go runtime does not use syscall.Time, it uses an implementation of nanotime(2), although that depends on the platform you are calling it on.

I see. And also runtime's getrlimit is implemented by ugetrlimit.
Yes, runtime's implementation looks like more sophisticated and well tested than syscall's one to me.

If there is a fix that needs to be made, it will be in the x/sys/unix package, the syscall package is closed for modifications.

Fair enough.

By the way, do you want to accept such a trivial bug report?
I know you guys work for more important issues everyday.
Maybe you don't want to spare time for trivial one.
Maybe you don't want to see the issue tracker is filled by trivial ones.
I don't want annoy you. That's not my intention.
So when I found a trivial issue, what should I do?

Thank you for responses, anyway.

[minux]

Trivial or not, if it's a bug, we need to fix it. If you think it's trivial, perhaps the best way is to just send a CL to fix it :) I think we need to fix x/sys/unix, and fix the syscall package if the fix is simple. (IIUC, the syscall package is frozen for non-bugfixes and additions except adding of new ports, but if the implementation of some existing functions is wrong, then we'd better fix it.) Reopen this issue.

[hirochachacha]

Thanks! I'll send a CL.

and fix the syscall package if the fix is simple.

Yes it's simple. For example, we can implement Time by gettimeofday,
Utime by utimes and Getrlimit by ugetrlimit.

But corresponding syscall numbers are already declaraed by api/go*.txt.
(i.e. SYS_TIME, SYS_UMOUNT, etc ...)

How can I treat these?

[davecheney]

@hirochachacha in general the syscall package exists to support the standard library. If the standard library does not need or use the function (even if it is buggy or not implemented), the preferred way is to fix it in the x/sys/unix repository.

[hirochachacha]

@davecheney I'm confusing. which should I follow?

[davecheney]

@hirochachacha we cannot change any of the public values declared in the syscall package. You may have to declare some private constants instead.

Also, please try to make as small as possible a fix. If the issue is not apparent to callers of this code, ie the rest of the standard library, the recommendation is to fix the issue in the x/sys/unix package instead.