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// Copyright 2018 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.
//go:build amd64 && linux
package runtime
import (
"internal/abi"
"internal/goarch"
"unsafe"
)
// InjectDebugCall injects a debugger call to fn into g. regArgs must
// contain any arguments to fn that are passed in registers, according
// to the internal Go ABI. It may be nil if no arguments are passed in
// registers to fn. args must be a pointer to a valid call frame (including
// arguments and return space) for fn, or nil. tkill must be a function that
// will send SIGTRAP to thread ID tid. gp must be locked to its OS thread and
// running.
//
// On success, InjectDebugCall returns the panic value of fn or nil.
// If fn did not panic, its results will be available in args.
func InjectDebugCall(gp *g, fn any, regArgs *abi.RegArgs, stackArgs any, tkill func(tid int) error, returnOnUnsafePoint bool) (any, error) {
if gp.lockedm == 0 {
return nil, plainError("goroutine not locked to thread")
}
tid := int(gp.lockedm.ptr().procid)
if tid == 0 {
return nil, plainError("missing tid")
}
f := efaceOf(&fn)
if f._type == nil || f._type.kind&kindMask != kindFunc {
return nil, plainError("fn must be a function")
}
fv := (*funcval)(f.data)
a := efaceOf(&stackArgs)
if a._type != nil && a._type.kind&kindMask != kindPtr {
return nil, plainError("args must be a pointer or nil")
}
argp := a.data
var argSize uintptr
if argp != nil {
argSize = (*ptrtype)(unsafe.Pointer(a._type)).elem.size
}
h := new(debugCallHandler)
h.gp = gp
// gp may not be running right now, but we can still get the M
// it will run on since it's locked.
h.mp = gp.lockedm.ptr()
h.fv, h.regArgs, h.argp, h.argSize = fv, regArgs, argp, argSize
h.handleF = h.handle // Avoid allocating closure during signal
defer func() { testSigtrap = nil }()
for i := 0; ; i++ {
testSigtrap = h.inject
noteclear(&h.done)
h.err = ""
if err := tkill(tid); err != nil {
return nil, err
}
// Wait for completion.
notetsleepg(&h.done, -1)
if h.err != "" {
switch h.err {
case "call not at safe point":
if returnOnUnsafePoint {
// This is for TestDebugCallUnsafePoint.
return nil, h.err
}
fallthrough
case "retry _Grunnable", "executing on Go runtime stack", "call from within the Go runtime":
// These are transient states. Try to get out of them.
if i < 100 {
usleep(100)
Gosched()
continue
}
}
return nil, h.err
}
return h.panic, nil
}
}
type debugCallHandler struct {
gp *g
mp *m
fv *funcval
regArgs *abi.RegArgs
argp unsafe.Pointer
argSize uintptr
panic any
handleF func(info *siginfo, ctxt *sigctxt, gp2 *g) bool
err plainError
done note
savedRegs sigcontext
savedFP fpstate1
}
func (h *debugCallHandler) inject(info *siginfo, ctxt *sigctxt, gp2 *g) bool {
// TODO(49370): This code is riddled with write barriers, but called from
// a signal handler. Add the go:nowritebarrierrec annotation and restructure
// this to avoid write barriers.
switch h.gp.atomicstatus {
case _Grunning:
if getg().m != h.mp {
println("trap on wrong M", getg().m, h.mp)
return false
}
// Push current PC on the stack.
rsp := ctxt.rsp() - goarch.PtrSize
*(*uint64)(unsafe.Pointer(uintptr(rsp))) = ctxt.rip()
ctxt.set_rsp(rsp)
// Write the argument frame size.
*(*uintptr)(unsafe.Pointer(uintptr(rsp - 16))) = h.argSize
// Save current registers.
h.savedRegs = *ctxt.regs()
h.savedFP = *h.savedRegs.fpstate
h.savedRegs.fpstate = nil
// Set PC to debugCallV2.
ctxt.set_rip(uint64(abi.FuncPCABIInternal(debugCallV2)))
// Call injected. Switch to the debugCall protocol.
testSigtrap = h.handleF
case _Grunnable:
// Ask InjectDebugCall to pause for a bit and then try
// again to interrupt this goroutine.
h.err = plainError("retry _Grunnable")
notewakeup(&h.done)
default:
h.err = plainError("goroutine in unexpected state at call inject")
notewakeup(&h.done)
}
// Resume execution.
return true
}
func (h *debugCallHandler) handle(info *siginfo, ctxt *sigctxt, gp2 *g) bool {
// TODO(49370): This code is riddled with write barriers, but called from
// a signal handler. Add the go:nowritebarrierrec annotation and restructure
// this to avoid write barriers.
// Double-check m.
if getg().m != h.mp {
println("trap on wrong M", getg().m, h.mp)
return false
}
f := findfunc(uintptr(ctxt.rip()))
if !(hasPrefix(funcname(f), "runtime.debugCall") || hasPrefix(funcname(f), "debugCall")) {
println("trap in unknown function", funcname(f))
return false
}
if *(*byte)(unsafe.Pointer(uintptr(ctxt.rip() - 1))) != 0xcc {
println("trap at non-INT3 instruction pc =", hex(ctxt.rip()))
return false
}
switch status := ctxt.r12(); status {
case 0:
// Frame is ready. Copy the arguments to the frame and to registers.
sp := ctxt.rsp()
memmove(unsafe.Pointer(uintptr(sp)), h.argp, h.argSize)
if h.regArgs != nil {
storeRegArgs(ctxt.regs(), h.regArgs)
}
// Push return PC.
sp -= goarch.PtrSize
ctxt.set_rsp(sp)
*(*uint64)(unsafe.Pointer(uintptr(sp))) = ctxt.rip()
// Set PC to call and context register.
ctxt.set_rip(uint64(h.fv.fn))
ctxt.regs().rdx = uint64(uintptr(unsafe.Pointer(h.fv)))
case 1:
// Function returned. Copy frame and result registers back out.
sp := ctxt.rsp()
memmove(h.argp, unsafe.Pointer(uintptr(sp)), h.argSize)
if h.regArgs != nil {
loadRegArgs(h.regArgs, ctxt.regs())
}
case 2:
// Function panicked. Copy panic out.
sp := ctxt.rsp()
memmove(unsafe.Pointer(&h.panic), unsafe.Pointer(uintptr(sp)), 2*goarch.PtrSize)
case 8:
// Call isn't safe. Get the reason.
sp := ctxt.rsp()
reason := *(*string)(unsafe.Pointer(uintptr(sp)))
h.err = plainError(reason)
// Don't wake h.done. We need to transition to status 16 first.
case 16:
// Restore all registers except RIP and RSP.
rip, rsp := ctxt.rip(), ctxt.rsp()
fp := ctxt.regs().fpstate
*ctxt.regs() = h.savedRegs
ctxt.regs().fpstate = fp
*fp = h.savedFP
ctxt.set_rip(rip)
ctxt.set_rsp(rsp)
// Done
notewakeup(&h.done)
default:
h.err = plainError("unexpected debugCallV2 status")
notewakeup(&h.done)
}
// Resume execution.
return true
}
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