From 0d05a12fd394e464d44d8d39c58b22249358ed19 Mon Sep 17 00:00:00 2001
From: Andrei Vagin <avagin@google.com>
Date: Wed, 12 Jun 2019 10:47:38 -0700
Subject: gvisor/ptrace: print guest registers if a stub stopped with
 unexpected code

PiperOrigin-RevId: 252855280
---
 pkg/sentry/platform/ptrace/subprocess.go       | 19 ++++++++++---
 pkg/sentry/platform/ptrace/subprocess_amd64.go | 37 ++++++++++++++++++++++++++
 2 files changed, 53 insertions(+), 3 deletions(-)

diff --git a/pkg/sentry/platform/ptrace/subprocess.go b/pkg/sentry/platform/ptrace/subprocess.go
index d3b196924..d7800a55e 100644
--- a/pkg/sentry/platform/ptrace/subprocess.go
+++ b/pkg/sentry/platform/ptrace/subprocess.go
@@ -21,6 +21,7 @@ import (
 	"sync"
 	"syscall"
 
+	"gvisor.googlesource.com/gvisor/pkg/log"
 	"gvisor.googlesource.com/gvisor/pkg/procid"
 	"gvisor.googlesource.com/gvisor/pkg/sentry/arch"
 	"gvisor.googlesource.com/gvisor/pkg/sentry/platform"
@@ -300,6 +301,18 @@ const (
 	killed
 )
 
+func (t *thread) dumpAndPanic(message string) {
+	var regs syscall.PtraceRegs
+	message += "\n"
+	if err := t.getRegs(&regs); err == nil {
+		message += dumpRegs(&regs)
+	} else {
+		log.Warningf("unable to get registers: %v", err)
+	}
+	message += fmt.Sprintf("stubStart\t = %016x\n", stubStart)
+	panic(message)
+}
+
 // wait waits for a stop event.
 //
 // Precondition: outcome is a valid waitOutcome.
@@ -320,7 +333,7 @@ func (t *thread) wait(outcome waitOutcome) syscall.Signal {
 		switch outcome {
 		case stopped:
 			if !status.Stopped() {
-				panic(fmt.Sprintf("ptrace status unexpected: got %v, wanted stopped", status))
+				t.dumpAndPanic(fmt.Sprintf("ptrace status unexpected: got %v, wanted stopped", status))
 			}
 			stopSig := status.StopSignal()
 			if stopSig == 0 {
@@ -334,12 +347,12 @@ func (t *thread) wait(outcome waitOutcome) syscall.Signal {
 			return stopSig
 		case killed:
 			if !status.Exited() && !status.Signaled() {
-				panic(fmt.Sprintf("ptrace status unexpected: got %v, wanted exited", status))
+				t.dumpAndPanic(fmt.Sprintf("ptrace status unexpected: got %v, wanted exited", status))
 			}
 			return syscall.Signal(status.ExitStatus())
 		default:
 			// Should not happen.
-			panic(fmt.Sprintf("unknown outcome: %v", outcome))
+			t.dumpAndPanic(fmt.Sprintf("unknown outcome: %v", outcome))
 		}
 	}
 }
diff --git a/pkg/sentry/platform/ptrace/subprocess_amd64.go b/pkg/sentry/platform/ptrace/subprocess_amd64.go
index 77a0e908f..fdd21c8f8 100644
--- a/pkg/sentry/platform/ptrace/subprocess_amd64.go
+++ b/pkg/sentry/platform/ptrace/subprocess_amd64.go
@@ -17,6 +17,8 @@
 package ptrace
 
 import (
+	"fmt"
+	"strings"
 	"syscall"
 
 	"gvisor.googlesource.com/gvisor/pkg/sentry/arch"
@@ -102,3 +104,38 @@ func syscallReturnValue(regs *syscall.PtraceRegs) (uintptr, error) {
 	}
 	return uintptr(rval), nil
 }
+
+func dumpRegs(regs *syscall.PtraceRegs) string {
+	var m strings.Builder
+
+	fmt.Fprintf(&m, "Registers:\n")
+	fmt.Fprintf(&m, "\tR15\t = %016x\n", regs.R15)
+	fmt.Fprintf(&m, "\tR14\t = %016x\n", regs.R14)
+	fmt.Fprintf(&m, "\tR13\t = %016x\n", regs.R13)
+	fmt.Fprintf(&m, "\tR12\t = %016x\n", regs.R12)
+	fmt.Fprintf(&m, "\tRbp\t = %016x\n", regs.Rbp)
+	fmt.Fprintf(&m, "\tRbx\t = %016x\n", regs.Rbx)
+	fmt.Fprintf(&m, "\tR11\t = %016x\n", regs.R11)
+	fmt.Fprintf(&m, "\tR10\t = %016x\n", regs.R10)
+	fmt.Fprintf(&m, "\tR9\t = %016x\n", regs.R9)
+	fmt.Fprintf(&m, "\tR8\t = %016x\n", regs.R8)
+	fmt.Fprintf(&m, "\tRax\t = %016x\n", regs.Rax)
+	fmt.Fprintf(&m, "\tRcx\t = %016x\n", regs.Rcx)
+	fmt.Fprintf(&m, "\tRdx\t = %016x\n", regs.Rdx)
+	fmt.Fprintf(&m, "\tRsi\t = %016x\n", regs.Rsi)
+	fmt.Fprintf(&m, "\tRdi\t = %016x\n", regs.Rdi)
+	fmt.Fprintf(&m, "\tOrig_rax = %016x\n", regs.Orig_rax)
+	fmt.Fprintf(&m, "\tRip\t = %016x\n", regs.Rip)
+	fmt.Fprintf(&m, "\tCs\t = %016x\n", regs.Cs)
+	fmt.Fprintf(&m, "\tEflags\t = %016x\n", regs.Eflags)
+	fmt.Fprintf(&m, "\tRsp\t = %016x\n", regs.Rsp)
+	fmt.Fprintf(&m, "\tSs\t = %016x\n", regs.Ss)
+	fmt.Fprintf(&m, "\tFs_base\t = %016x\n", regs.Fs_base)
+	fmt.Fprintf(&m, "\tGs_base\t = %016x\n", regs.Gs_base)
+	fmt.Fprintf(&m, "\tDs\t = %016x\n", regs.Ds)
+	fmt.Fprintf(&m, "\tEs\t = %016x\n", regs.Es)
+	fmt.Fprintf(&m, "\tFs\t = %016x\n", regs.Fs)
+	fmt.Fprintf(&m, "\tGs\t = %016x\n", regs.Gs)
+
+	return m.String()
+}
-- 
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