by lucio.dere:

What steps will reproduce the problem?

This is build time problem: the test sequence fails irregularly with a bad file
descriptor for the fork/exec operation.

What is the expected output?

Successful loading of one or more test programs.

What do you see instead?

An error report on failure to load because of an invalid file descriptor.

Which compiler are you using (5g, 6g, 8g, gccgo)?

The Go build suite, in this case for the 386 architecture.

Which operating system are you using?

Plan 9.

Which version are you using?  (run 'go version')

"tip"

Details:

The current code in the module from around line 186 has been declared
flawed in that it seems to handle some conditions incorrectly.

I'd like to propose the following correction - based on the assumption
that the comment is correct:

        // Guard against side effects of shuffling fds below.
        // Make sure that nextfd is beyond any currently open files so
        // that we can't run the risk of overwriting any of them.
        nextfd = len(attr.Files)
        fd := make([]int, nextfd)
        for i, ufd := range attr.Files {
                if nextfd < int(ufd) {
                        nextfd = int(ufd) + 1
                }
                fd[i] = int(ufd)
        }
        fd = append(fd, nextfd)

I'm busy with a complicated code synchronisation problem right now, so
I can't test my proposal immediately.  Anybody is welcome to address
the problem in my stead.

Lucio.

PS: Actually, I think the above can be programmed more defensively,
without making any assumptions about the relationship between the
number of fds and their values.