APP CRASH: Missing handling of stack ptr == NULL in clone(CLONE_VFORK + CLONE_VM)

[xdje42]

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Describe the bug

The Go process spawn support invokes clone() with CLONE_VFORK + CLONE_VM + stack_ptr == NULL. Glibc doesn't support this but the syscall itself does. stack_ptr == NULL means set $sp in the child to be $sp in the parent. This is dangerous, but the use of CLONE_VFORK makes this workable.

DR doesn't handle this causing the app to get a segv when it references values off of $sp (== NULL in the child).

To Reproduce

$ cat >test-exec.go <<EOF
package main
import (
        "fmt"
        "os/exec"
)
func main() {
        cmd := exec.Command("/bin/echo", "xyz")
        out, err := cmd.CombinedOutput()
        fmt.Printf("%s\n", out)
        println(err)
        println("Done")
}
EOF
$ go build test-exec.go
$ drrun -- ./test-exec

--> signal 11 received during fork fatal error: signal received during fork

Please also answer these questions:

• What happens when you run without any client? Program runs to completion
• What happens when you run with debug build ("-debug" flag to drrun/drconfig/drinject)? Same segv

Expected behavior

Program runs to completion.

Screenshots or Pasted Text

None

Versions

git master @6d1912f6f6655b9185aa6fc73243819c8e905cac on amd64 linux

Additional context

None

[xdje42]

Hmm. The repro example got deleted (it was a here document).

package main
import (
	"fmt"
	"os/exec"
)
func main() {
	cmd := exec.Command("/bin/echo", "xyz")
	out, err := cmd.CombinedOutput()
	fmt.Printf("%s\n", out)
	println(err)
	println("Done")
}

$ go build test-exec.go
$ drrun -- ./test-exec

[derekbruening]

It wasn't deleted: hidden by the markdown. I clicked "edit" and fixed the markdown in the original comment.

[xdje42]

No issues reported since merging. Closing.