all: move -panic=trap support to the compiler/runtime

Support for `-panic=trap` was previously a pass in the optimization
pipeline. This change moves it to the compiler and runtime, which in my
opinion is a much better place.

As a side effect, it also fixes
#4161 by trapping inside
runtime.runtimePanicAt and not just runtime.runtimePanic.

This change also adds a test for the list of imported functions. This is
a more generic test where it's easy to add more tests for WebAssembly
file properties, such as exported functions.

builder/build.go

@@ -200,6 +200,7 @@ func Build(pkgName, outpath, tmpdir string, config *compileopts.Config) (BuildRe
 		MaxStackAlloc:      config.MaxStackAlloc(),
 		NeedsStackObjects:  config.NeedsStackObjects(),
 		Debug:              !config.Options.SkipDWARF, // emit DWARF except when -internal-nodwarf is passed
+		PanicStrategy:      config.PanicStrategy(),
 	}
 
 	// Load the target machine, which is the LLVM object that contains all

compiler/compiler.go

@@ -56,6 +56,7 @@ type Config struct {
 	MaxStackAlloc      uint64
 	NeedsStackObjects  bool
 	Debug              bool // Whether to emit debug information in the LLVM module.
+	PanicStrategy      string
 }
 
 // compilerContext contains function-independent data that should still be
@@ -1855,6 +1856,13 @@ func (b *builder) createFunctionCall(instr *ssa.CallCommon) (llvm.Value, error)
 				supportsRecover = 1
 			}
 			return llvm.ConstInt(b.ctx.Int1Type(), supportsRecover, false), nil
+		case name == "runtime.panicStrategy":
+			// These constants are defined in src/runtime/panic.go.
+			panicStrategy := map[string]uint64{
+				"print": 1, // panicStrategyPrint
+				"trap":  2, // panicStrategyTrap
+			}[b.Config.PanicStrategy]
+			return llvm.ConstInt(b.ctx.Int8Type(), panicStrategy, false), nil
 		case name == "runtime/interrupt.New":
 			return b.createInterruptGlobal(instr)
 		}

main_test.go

@@ -15,11 +15,13 @@ import (
 	"reflect"
 	"regexp"
 	"runtime"
+	"slices"
 	"strings"
 	"sync"
 	"testing"
 	"time"
 
+	"github.com/aykevl/go-wasm"
 	"github.com/tinygo-org/tinygo/builder"
 	"github.com/tinygo-org/tinygo/compileopts"
 	"github.com/tinygo-org/tinygo/goenv"
@@ -404,6 +406,64 @@ func runTestWithConfig(name string, t *testing.T, options compileopts.Options, c
 	}
 }
 
+// Test WebAssembly files for certain properties.
+func TestWebAssembly(t *testing.T) {
+	t.Parallel()
+	type testCase struct {
+		name          string
+		panicStrategy string
+		imports       []string
+	}
+	for _, tc := range []testCase{
+		// Test whether there really are no imports when using -panic=trap. This
+		// tests the bugfix for https://github.com/tinygo-org/tinygo/issues/4161.
+		{name: "panic-default", imports: []string{"wasi_snapshot_preview1.fd_write"}},
+		{name: "panic-trap", panicStrategy: "trap", imports: []string{}},
+	} {
+		tc := tc
+		t.Run(tc.name, func(t *testing.T) {
+			t.Parallel()
+			tmpdir := t.TempDir()
+			options := optionsFromTarget("wasi", sema)
+			options.PanicStrategy = tc.panicStrategy
+			config, err := builder.NewConfig(&options)
+			if err != nil {
+				t.Fatal(err)
+			}
+
+			result, err := builder.Build("testdata/trivialpanic.go", ".wasm", tmpdir, config)
+			if err != nil {
+				t.Fatal("failed to build binary:", err)
+			}
+			f, err := os.Open(result.Binary)
+			if err != nil {
+				t.Fatal("could not open output binary:", err)
+			}
+			defer f.Close()
+			module, err := wasm.Parse(f)
+			if err != nil {
+				t.Fatal("could not parse output binary:", err)
+			}
+
+			// Test the list of imports.
+			if tc.imports != nil {
+				var imports []string
+				for _, section := range module.Sections {
+					switch section := section.(type) {
+					case *wasm.SectionImport:
+						for _, symbol := range section.Entries {
+							imports = append(imports, symbol.Module+"."+symbol.Field)
+						}
+					}
+				}
+				if !slices.Equal(imports, tc.imports) {
+					t.Errorf("import list not as expected!\nexpected: %v\nactual:   %v", tc.imports, imports)
+				}
+			}
+		})
+	}
+}
+
 func TestTest(t *testing.T) {
 	t.Parallel()
 

src/runtime/panic.go

@@ -21,6 +21,16 @@ func tinygo_longjmp(frame *deferFrame)
 // Returns whether recover is supported on the current architecture.
 func supportsRecover() bool
 
+const (
+	panicStrategyPrint = 1
+	panicStrategyTrap  = 2
+)
+
+// Compile intrinsic.
+// Returns which strategy is used. This is usually "print" but can be changed
+// using the -panic= compiler flag.
+func panicStrategy() uint8
+
 // DeferFrame is a stack allocated object that stores information for the
 // current "defer frame", which is used in functions that use the `defer`
 // keyword.
@@ -37,6 +47,9 @@ type deferFrame struct {
 
 // Builtin function panic(msg), used as a compiler intrinsic.
 func _panic(message interface{}) {
+	if panicStrategy() == panicStrategyTrap {
+		trap()
+	}
 	if supportsRecover() {
 		frame := (*deferFrame)(task.Current().DeferFrame)
 		if frame != nil {
@@ -60,6 +73,9 @@ func runtimePanic(msg string) {
 }
 
 func runtimePanicAt(addr unsafe.Pointer, msg string) {
+	if panicStrategy() == panicStrategyTrap {
+		trap()
+	}
 	if hasReturnAddr {
 		printstring("panic: runtime error at ")
 		printptr(uintptr(addr) - callInstSize)

transform/optimizer.go

@@ -40,10 +40,6 @@ func Optimize(mod llvm.Module, config *compileopts.Config) []error {
 		fn.SetLinkage(llvm.ExternalLinkage)
 	}
 
-	if config.PanicStrategy() == "trap" {
-		ReplacePanicsWithTrap(mod) // -panic=trap
-	}
-
 	// run a check of all of our code
 	if config.VerifyIR() {
 		errs := ircheck.Module(mod)

transform/transform_test.go

@@ -137,6 +137,7 @@ func compileGoFileForTesting(t *testing.T, filename string) llvm.Module {
 		Scheduler:          config.Scheduler(),
 		AutomaticStackSize: config.AutomaticStackSize(),
 		Debug:              true,
+		PanicStrategy:      config.PanicStrategy(),
 	}
 	machine, err := compiler.NewTargetMachine(compilerConfig)
 	if err != nil {