tests/fixedbugs: make test for issue11656 run known instruction

As detailed in #11910, the current implementation attempts to execute an area
of memory with unknown content. If the memory is executable, the result is
unpredictable - instead, make the test deterministic by attempting to execute
an instruction that is known to trigger a trap on the given architecture.

The new implementation is written by iant@ and provided via #11910.

Update issue #11910

Change-Id: Ia698c36e0dd98a9d9d16a701f60f6748c6faf896
Reviewed-on: https://go-review.googlesource.com/15058
Run-TryBot: Joel Sing <jsing@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>

diff --git a/test/fixedbugs/issue11656.go b/test/fixedbugs/issue11656.go
index 90385bbdc47b70b24a55369ffb477362fe2ae0ae..bbedb43bc66aac2957816e5a0ad5040bd12fdca8 100644 (file)
--- a/test/fixedbugs/issue11656.go
+++ b/test/fixedbugs/issue11656.go
@@ -4,26 +4,15 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
-// darwin/386 seems to mangle the PC and SP before
-// it manages to invoke the signal handler, so this test fails there.
-// +build !darwin !386
-//
-// openbsd/386 and netbsd/386 don't work, not sure why.
-// +build !openbsd !386
-// +build !netbsd !386
-//
 // windows doesn't work, because Windows exception handling
 // delivers signals based on the current PC, and that current PC
 // doesn't go into the Go runtime.
 // +build !windows
-//
-// arm64 gets "illegal instruction" (why is the data executable?)
-// and is unable to do the traceback correctly (why?).
-// +build !arm64
 
 package main
 
 import (
+       "encoding/binary"
        "runtime"
        "runtime/debug"
        "unsafe"
@@ -56,7 +45,27 @@ func f(n int) {
        var f struct {
                x uintptr
        }
-       f.x = uintptr(unsafe.Pointer(&f))
+
+       // We want to force an illegal instruction, to get a crash
+       // at a PC value != 0.
+       // Not all systems make the data section non-executable.
+       ill := make([]byte, 64)
+       switch runtime.GOARCH {
+       case "386", "amd64":
+               binary.LittleEndian.PutUint16(ill, 0x0b0f) // ud2
+       case "arm":
+               binary.LittleEndian.PutUint32(ill, 0xe7f000f0) // no name, but permanently undefined
+       case "arm64":
+               binary.LittleEndian.PutUint32(ill, 0xd4207d00) // brk #1000
+       case "ppc64":
+               binary.BigEndian.PutUint32(ill, 0x7fe00008) // trap
+       case "ppc64le":
+               binary.LittleEndian.PutUint32(ill, 0x7fe00008) // trap
+       default:
+               // Just leave it as 0 and hope for the best.
+       }
+
+       f.x = uintptr(unsafe.Pointer(&ill[0]))
        fn := *(*func())(unsafe.Pointer(&f))
        fn()
 }