compiler_wrapper: add flag to skip automatic sysroot logic

Adding `--sysroot` and the implicit library path here breaks glibc's
build when `llvm-libunwind` is installed. Since glibc is a special
package, it seems OK to let it own its own destiny WRT gathering the
proper includes & linking to libraries properly.

BUG=b:290144273
TEST=emerge glibc

Change-Id: I4f814b39334147631a0fdcb67ad1f0e067e1d674
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/third_party/toolchain-utils/+/4678360
Reviewed-by: Jordan Abrahams-Whitehead <ajordanr@google.com>
Tested-by: George Burgess <gbiv@chromium.org>
Commit-Queue: George Burgess <gbiv@chromium.org>

2 files changed, 47 insertions, 3 deletions

diff --git a/compiler_wrapper/sysroot_flag.go b/compiler_wrapper/sysroot_flag.go
index 597153a9..0256abcd 100644
--- a/compiler_wrapper/sysroot_flag.go
+++ b/compiler_wrapper/sysroot_flag.go
@@ -9,19 +9,37 @@ import (
 	"strings"
 )
 
+const skipSysrootAutodetectionFlag = "--cros-skip-wrapper-sysroot-autodetection"
+
 func processSysrootFlag(builder *commandBuilder) {
+	hadSkipSysrootMagicFlag := false
 	fromUser := false
 	userSysroot := ""
-	for _, arg := range builder.args {
-		if arg.fromUser && strings.HasPrefix(arg.value, "--sysroot=") {
+	builder.transformArgs(func(arg builderArg) string {
+		switch {
+		// In rare cases (e.g., glibc), we want all sysroot autodetection logic to be
+		// disabled. This flag can be passed to disable that.
+		case arg.value == skipSysrootAutodetectionFlag:
+			hadSkipSysrootMagicFlag = true
+			return ""
+
+		case arg.fromUser && strings.HasPrefix(arg.value, "--sysroot="):
 			fromUser = true
 			sysrootArg := strings.Split(arg.value, "=")
 			if len(sysrootArg) == 2 {
 				userSysroot = sysrootArg[1]
 			}
-			break
+			return arg.value
+
+		default:
+			return arg.value
 		}
+	})
+
+	if hadSkipSysrootMagicFlag {
+		return
 	}
+
 	sysroot, syrootPresent := builder.env.getenv("SYSROOT")
 	if syrootPresent {
 		builder.updateEnv("SYSROOT=")
diff --git a/compiler_wrapper/sysroot_flag_test.go b/compiler_wrapper/sysroot_flag_test.go
index 9fea6848..bca8d1b0 100644
--- a/compiler_wrapper/sysroot_flag_test.go
+++ b/compiler_wrapper/sysroot_flag_test.go
@@ -6,9 +6,35 @@ package main
 
 import (
 	"path"
+	"regexp"
 	"testing"
 )
 
+func TestOmitSysrootGivenSysrootSuppressionFlag(t *testing.T) {
+	escapedAutodetectionFlag := regexp.QuoteMeta(skipSysrootAutodetectionFlag)
+	withTestContext(t, func(ctx *testContext) {
+		runWithCompiler := func(compiler string) {
+			cmd := ctx.must(callCompiler(ctx, ctx.cfg,
+				ctx.newCommand(compiler, skipSysrootAutodetectionFlag, mainCc)))
+			if err := verifyArgOrder(cmd, mainCc); err != nil {
+				t.Error(err)
+			}
+			if err := verifyArgCount(cmd, 0, "--sysroot.*"); err != nil {
+				t.Error(err)
+			}
+			if err := verifyArgCount(cmd, 0, "-L.*"); err != nil {
+				t.Error(err)
+			}
+			if err := verifyArgCount(cmd, 0, escapedAutodetectionFlag); err != nil {
+				t.Error(err)
+			}
+		}
+
+		runWithCompiler(gccX86_64)
+		runWithCompiler(clangX86_64)
+	})
+}
+
 func TestOmitSysrootGivenUserDefinedSysroot(t *testing.T) {
 	withTestContext(t, func(ctx *testContext) {
 		runWithCompiler := func(compiler string) {