pkg/kernel: allow to split full make output

Currently kernel build failures are insanely verbose
(contain full kernel build output) and there is no
way to separate short descriptions from full output.
Make it possible.
Also try to extract failure root cause froom build log.
Use this in pkg/bisect to not pollute log on build failures.

Update #501

1 files changed, 41 insertions, 2 deletions

diff --git a/pkg/kernel/kernel.go b/pkg/kernel/kernel.go
index 21612f10a..454ed8eb3 100644
--- a/pkg/kernel/kernel.go
+++ b/pkg/kernel/kernel.go
@@ -12,6 +12,7 @@
 package kernel
 
 import (
+	"bytes"
 	"fmt"
 	"io/ioutil"
 	"os"
@@ -50,8 +51,10 @@ func Build(dir, compiler string, config []byte) error {
 	}
 	cmd.Dir = dir
 	// Build of a large kernel can take a while on a 1 CPU VM.
-	_, err := osutil.Run(3*time.Hour, cmd)
-	return err
+	if _, err := osutil.Run(3*time.Hour, cmd); err != nil {
+		return extractRootCause(err)
+	}
+	return nil
 }
 
 func Clean(dir string) error {
@@ -122,3 +125,39 @@ func CompilerIdentity(compiler string) (string, error) {
 	}
 	return strings.Split(string(output), "\n")[0], nil
 }
+
+func extractRootCause(err error) error {
+	verr, ok := err.(*osutil.VerboseError)
+	if !ok {
+		return err
+	}
+	var cause []byte
+	for _, line := range bytes.Split(verr.Output, []byte{'\n'}) {
+		for _, pattern := range buildFailureCauses {
+			if pattern.weak && cause != nil {
+				continue
+			}
+			if bytes.Contains(line, pattern.pattern) {
+				cause = line
+				break
+			}
+		}
+	}
+	if cause != nil {
+		verr.Title = string(cause)
+	}
+	return verr
+}
+
+type buildFailureCause struct {
+	pattern []byte
+	weak    bool
+}
+
+var buildFailureCauses = [...]buildFailureCause{
+	{pattern: []byte(": error: ")},
+	{pattern: []byte(": fatal error: ")},
+	{pattern: []byte(": undefined reference to")},
+	{weak: true, pattern: []byte(": final link failed: ")},
+	{weak: true, pattern: []byte("collect2: error: ")},
+}