pkg/compiler: allow manual consts to override auto-extracted consts

Currently if const values in 2 .const files have different value,
the compiler produces an error.
This is problematic for auto-extacted consts since we extract
them for only 1 arch now. So if a const has different values
for different arches, auto-extacted consts may not reflect that,
and we can get a mismatch with manual descriptions that has
correct values for all arches.
So if both manual and auto-extacted consts have different values,
silently prefer the manual ones.

I've tried to do some whitelisting of consts during auto-extaction,
but the list is large and changing over time.

This solution is not perfect since the manual descriptions may
have a bug, and the mismatch is actually pointing to that bug.
Maybe in future we could extract for all arches separately,
or do something else. But let's do this for now.

7 files changed, 67 insertions, 13 deletions

diff --git a/pkg/compiler/compiler_test.go b/pkg/compiler/compiler_test.go
index f43b2ccb3..711567163 100644
--- a/pkg/compiler/compiler_test.go
+++ b/pkg/compiler/compiler_test.go
@@ -137,6 +137,27 @@ func TestData(t *testing.T) {
 	}
 }
 
+func TestAutoConsts(t *testing.T) {
+	t.Parallel()
+	eh := func(pos ast.Pos, msg string) {
+		t.Errorf("%v: %v", pos, msg)
+	}
+	desc := ast.ParseGlob(filepath.Join("testdata", "auto*.txt"), eh)
+	if desc == nil {
+		t.Fatalf("parsing failed")
+	}
+	constFile := DeserializeConstFile(filepath.Join("testdata", "auto*.txt.const"), eh)
+	if constFile == nil {
+		t.Fatalf("const loading failed")
+	}
+	target := targets.List[targets.TestOS][targets.TestArch64]
+	consts := constFile.Arch(targets.TestArch64)
+	prog := Compile(desc, consts, target, eh)
+	if prog == nil {
+		t.Fatalf("compilation failed")
+	}
+}
+
 func TestFuzz(t *testing.T) {
 	t.Parallel()
 	for _, data := range []string{
diff --git a/pkg/compiler/const_file.go b/pkg/compiler/const_file.go
index 1968092a4..0220da555 100644
--- a/pkg/compiler/const_file.go
+++ b/pkg/compiler/const_file.go
@@ -26,6 +26,10 @@ type ConstFile struct {
 type constVal struct {
 	name string
 	vals map[string]uint64 // arch -> value
+	// Set if the value for the arch is weak (come from auto.txt).
+	// Weak values are replaced on mismatch, instead of producing
+	// an error about mismatching values.
+	weak map[string]bool
 }
 
 const undefined = "???"
@@ -40,30 +44,38 @@ func NewConstFile() *ConstFile {
 func (cf *ConstFile) AddArch(arch string, consts map[string]uint64, undeclared map[string]bool) error {
 	cf.arches[arch] = true
 	for name, val := range consts {
-		if err := cf.addConst(arch, name, val, true); err != nil {
+		if err := cf.addConst(arch, name, val, true, false); err != nil {
 			return err
 		}
 	}
 	for name := range undeclared {
-		if err := cf.addConst(arch, name, 0, false); err != nil {
+		if err := cf.addConst(arch, name, 0, false, false); err != nil {
 			return err
 		}
 	}
 	return nil
 }
 
-func (cf *ConstFile) addConst(arch, name string, val uint64, declared bool) error {
+func (cf *ConstFile) addConst(arch, name string, val uint64, declared, weak bool) error {
 	cv := cf.m[name]
 	if cv.vals == nil {
 		cv.name = name
 		cv.vals = make(map[string]uint64)
-	}
-	if val0, declared0 := cv.vals[arch]; declared && declared0 && val != val0 {
-		return fmt.Errorf("const=%v arch=%v has different values: %v[%v] vs %v[%v]",
-			name, arch, val, declared, val0, declared0)
+		cv.weak = make(map[string]bool)
 	}
 	if declared {
+		val0, declared0 := cv.vals[arch]
+		if declared0 {
+			if weak {
+				return nil
+			}
+			if !cv.weak[arch] && val != val0 {
+				return fmt.Errorf("const=%v arch=%v has different values: %v[%v] vs %v[%v]",
+					name, arch, val, declared, val0, declared0)
+			}
+		}
 		cv.vals[arch] = val
+		cv.weak[arch] = weak
 	}
 	cf.m[name] = cv
 	return nil
@@ -196,6 +208,7 @@ func (cf *ConstFile) deserializeFile(data []byte, file, arch string, eh ast.Erro
 		eh(pos, fmt.Sprintf(msg, args...))
 		return false
 	}
+	weak := file == "auto.txt.const"
 	s := bufio.NewScanner(bytes.NewReader(data))
 	var arches []string
 	for ; s.Scan(); pos.Line++ {
@@ -224,7 +237,7 @@ func (cf *ConstFile) deserializeFile(data []byte, file, arch string, eh ast.Erro
 			}
 			continue
 		}
-		if !cf.parseConst(arches, name, val, errf) {
+		if !cf.parseConst(arches, name, val, weak, errf) {
 			return false
 		}
 	}
@@ -236,7 +249,7 @@ func (cf *ConstFile) deserializeFile(data []byte, file, arch string, eh ast.Erro
 
 type errft func(msg string, args ...interface{}) bool
 
-func (cf *ConstFile) parseConst(arches []string, name, line string, errf errft) bool {
+func (cf *ConstFile) parseConst(arches []string, name, line string, weak bool, errf errft) bool {
 	var dflt map[string]uint64
 	for _, pair := range strings.Split(line, ",") {
 		fields := strings.Split(pair, ":")
@@ -274,13 +287,13 @@ func (cf *ConstFile) parseConst(arches []string, name, line string, errf errft)
 		for _, arch := range fields[:len(fields)-1] {
 			arch = strings.TrimSpace(arch)
 			delete(dflt, arch)
-			if err := cf.addConst(arch, name, val, defined); err != nil {
+			if err := cf.addConst(arch, name, val, defined, weak); err != nil {
 				return errf("%v", err)
 			}
 		}
 	}
 	for arch, val := range dflt {
-		if err := cf.addConst(arch, name, val, true); err != nil {
+		if err := cf.addConst(arch, name, val, true, weak); err != nil {
 			return errf("%v", err)
 		}
 	}
@@ -292,7 +305,7 @@ func (cf *ConstFile) parseOldConst(arch, name, line string, errf errft) bool {
 	if err != nil {
 		return errf("failed to parse int: %v", err)
 	}
-	if err := cf.addConst(arch, name, val, true); err != nil {
+	if err := cf.addConst(arch, name, val, true, false); err != nil {
 		return errf("%v", err)
 	}
 	return true
diff --git a/pkg/compiler/consts.go b/pkg/compiler/consts.go
index 62de4aa51..5e1ed9188 100644
--- a/pkg/compiler/consts.go
+++ b/pkg/compiler/consts.go
@@ -42,7 +42,7 @@ func FabricateSyscallConsts(target *targets.Target, constInfo map[string]*ConstI
 	for _, info := range constInfo {
 		for _, c := range info.Consts {
 			if strings.HasPrefix(c.Name, target.SyscallPrefix) {
-				cf.addConst(target.Arch, c.Name, 0, true)
+				cf.addConst(target.Arch, c.Name, 0, true, false)
 			}
 		}
 	}
diff --git a/pkg/compiler/testdata/auto.txt b/pkg/compiler/testdata/auto.txt
new file mode 100644
index 000000000..1e64e0a95
--- /dev/null
+++ b/pkg/compiler/testdata/auto.txt
@@ -0,0 +1,4 @@
+# Copyright 2024 syzkaller project authors. All rights reserved.
+# Use of this source code is governed by Apache 2 LICENSE that can be found in the LICENSE file.
+
+foo(a const[FOO])
diff --git a/pkg/compiler/testdata/auto.txt.const b/pkg/compiler/testdata/auto.txt.const
new file mode 100644
index 000000000..388aa936f
--- /dev/null
+++ b/pkg/compiler/testdata/auto.txt.const
@@ -0,0 +1,6 @@
+# Copyright 2024 syzkaller project authors. All rights reserved.
+# Use of this source code is governed by Apache 2 LICENSE that can be found in the LICENSE file.
+
+arches = 64
+SYS_foo = 11
+FOO = 22
diff --git a/pkg/compiler/testdata/auto0.txt b/pkg/compiler/testdata/auto0.txt
new file mode 100644
index 000000000..9c3608caf
--- /dev/null
+++ b/pkg/compiler/testdata/auto0.txt
@@ -0,0 +1,4 @@
+# Copyright 2024 syzkaller project authors. All rights reserved.
+# Use of this source code is governed by Apache 2 LICENSE that can be found in the LICENSE file.
+
+foo$auto(a const[FOO])
diff --git a/pkg/compiler/testdata/auto0.txt.const b/pkg/compiler/testdata/auto0.txt.const
new file mode 100644
index 000000000..4ba494b07
--- /dev/null
+++ b/pkg/compiler/testdata/auto0.txt.const
@@ -0,0 +1,6 @@
+# Copyright 2024 syzkaller project authors. All rights reserved.
+# Use of this source code is governed by Apache 2 LICENSE that can be found in the LICENSE file.
+
+arches = 64
+SYS_foo = 1
+FOO = 2