Add runsc symbolize command.

This command takes instruction pointers from stdin and converts them into their
corresponding file names and line/column numbers in the runsc source code. The
inputs are not interpreted as actual addresses, but as synthetic values that are
exposed through /sys/kernel/debug/kcov. One can extract coverage information
from kcov and translate those values into locations in the source code by
running symbolize on the same runsc binary.

This will allow us to generate syzkaller coverage reports.

PiperOrigin-RevId: 347089624

2 files changed, 93 insertions, 0 deletions

diff --git a/runsc/cmd/BUILD b/runsc/cmd/BUILD
index 2556f6d9e..19520d7ab 100644
--- a/runsc/cmd/BUILD
+++ b/runsc/cmd/BUILD
@@ -32,6 +32,7 @@ go_library(
         "start.go",
         "state.go",
         "statefile.go",
+        "symbolize.go",
         "syscalls.go",
         "wait.go",
     ],
@@ -39,6 +40,7 @@ go_library(
         "//runsc:__subpackages__",
     ],
     deps = [
+        "//pkg/coverage",
         "//pkg/log",
         "//pkg/p9",
         "//pkg/sentry/control",
diff --git a/runsc/cmd/symbolize.go b/runsc/cmd/symbolize.go
new file mode 100644
index 000000000..fc0c69358
--- /dev/null
+++ b/runsc/cmd/symbolize.go
@@ -0,0 +1,91 @@
+// Copyright 2020 The gVisor Authors.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package cmd
+
+import (
+	"bufio"
+	"context"
+	"os"
+	"strconv"
+	"strings"
+
+	"github.com/google/subcommands"
+	"gvisor.dev/gvisor/pkg/coverage"
+	"gvisor.dev/gvisor/runsc/flag"
+)
+
+// Symbolize implements subcommands.Command for the "symbolize" command.
+type Symbolize struct {
+	dumpAll bool
+}
+
+// Name implements subcommands.Command.Name.
+func (*Symbolize) Name() string {
+	return "symbolize"
+}
+
+// Synopsis implements subcommands.Command.Synopsis.
+func (*Symbolize) Synopsis() string {
+	return "Convert synthetic instruction pointers from kcov into positions in the runsc source code. Only used when Go coverage is enabled."
+}
+
+// Usage implements subcommands.Command.Usage.
+func (*Symbolize) Usage() string {
+	return `symbolize - converts synthetic instruction pointers into positions in the runsc source code.
+
+This command takes instruction pointers from stdin and converts them into their
+corresponding file names and line/column numbers in the runsc source code. The
+inputs are not interpreted as actual addresses, but as synthetic values that are
+exposed through /sys/kernel/debug/kcov. One can extract coverage information
+from kcov and translate those values into locations in the source code by
+running symbolize on the same runsc binary.
+`
+}
+
+// SetFlags implements subcommands.Command.SetFlags.
+func (c *Symbolize) SetFlags(f *flag.FlagSet) {
+	f.BoolVar(&c.dumpAll, "all", false, "dump information on all coverage blocks along with their synthetic PCs")
+}
+
+// Execute implements subcommands.Command.Execute.
+func (c *Symbolize) Execute(_ context.Context, f *flag.FlagSet, args ...interface{}) subcommands.ExitStatus {
+	if f.NArg() != 0 {
+		f.Usage()
+		return subcommands.ExitUsageError
+	}
+	if !coverage.KcovAvailable() {
+		return Errorf("symbolize can only be used when coverage is available.")
+	}
+	coverage.InitCoverageData()
+
+	if c.dumpAll {
+		coverage.WriteAllBlocks(os.Stdout)
+		return subcommands.ExitSuccess
+	}
+
+	scanner := bufio.NewScanner(os.Stdin)
+	for scanner.Scan() {
+		// Input is always base 16, but may or may not have a leading "0x".
+		str := strings.TrimPrefix(scanner.Text(), "0x")
+		pc, err := strconv.ParseUint(str, 16 /* base */, 64 /* bitSize */)
+		if err != nil {
+			return Errorf("Failed to symbolize \"%s\": %v", scanner.Text(), err)
+		}
+		if err := coverage.Symbolize(os.Stdout, pc); err != nil {
+			return Errorf("Failed to symbolize \"%s\": %v", scanner.Text(), err)
+		}
+	}
+	return subcommands.ExitSuccess
+}