feat(asm): encode indirect JMP and CALL on all four architectures

Assisted-by: GLM 5.3 Flash

lint/lint.go

@@ -209,10 +209,10 @@ func lintText(t *ast.Text, tab *arch.Table, archKnown bool, cfg Config, macros m
 	lastTerminal := false
 	hasMacro := false
 	instrCount := 0
-	dead := false                       // inside a region unreachable from above
-	reportedDead := false               // the current dead region has already been reported
-	hasPCRel := referencesPC(t)         // PC-relative jumps defeat reachability analysis
-	hasIndirect := hasIndirectBranch(t) // register-indirect branches do too
+	dead := false                            // inside a region unreachable from above
+	reportedDead := false                    // the current dead region has already been reported
+	hasPCRel := referencesPC(t)              // PC-relative jumps defeat reachability analysis
+	hasIndirect := hasIndirectBranch(t, tab) // register-indirect branches do too
 	// Unreachable-code analysis is only sound in functions whose control flow is
 	// fully label-resolvable: no PC-relative jumps, no register-indirect
 	// branches, and (file-level) no preprocessor conditionals.
@@ -549,10 +549,12 @@ func referencesPC(t *ast.Text) bool {
 }
 
 // hasIndirectBranch reports whether a function transfers control through a
-// register (JALR/JR/JIRL/BR/BLR).  Such targets are computed at runtime, so
-// reachability cannot be determined statically and the unreachable-code check is
-// suppressed for the whole function.
-func hasIndirectBranch(t *ast.Text) bool {
+// register or a computed memory address: the RISC branch-register mnemonics
+// (JALR/JR/JIRL/BR/BLR), or a JMP/CALL whose target is a register or memory
+// operand rather than a label or symbol.  Such targets are computed at
+// runtime, so reachability cannot be determined statically and the
+// unreachable-code check is suppressed for the whole function.
+func hasIndirectBranch(t *ast.Text, tab *arch.Table) bool {
 	for _, s := range t.Body {
 		in, ok := s.(*ast.Instr)
 		if !ok {
@@ -561,11 +563,30 @@ func hasIndirectBranch(t *ast.Text) bool {
 		switch strings.ToUpper(in.Mnemonic.Text) {
 		case "JALR", "JR", "JIRL", "BR", "BLR":
 			return true
+		case "JMP", "CALL":
+			if indirectJumpTarget(in, tab) {
+				return true
+			}
 		}
 	}
 	return false
 }
 
+// indirectJumpTarget reports whether the JMP/CALL operand addresses a
+// register or a memory location rather than a label or a static symbol.  The
+// parser delivers a bare register and a bare label in the same shape, so
+// register membership decides.
+func indirectJumpTarget(in *ast.Instr, tab *arch.Table) bool {
+	if len(in.Operands) != 1 || in.Operands[0].Kind != ast.OpAddr {
+		return false
+	}
+	a := in.Operands[0].Addr
+	if a.Base != "" || a.Index != "" {
+		return true
+	}
+	return a.Sym != nil && a.Sym.Pseudo == "" && a.Sym.Name != "" && tab.IsRegister(a.Sym.Name)
+}
+
 // isMacroInvocation reports whether a mnemonic is a macro invocation rather
 // than a machine instruction.  No Plan 9 mnemonic contains an underscore, so an
 // underscore is a reliable macro marker (the runtime headers define macros such

lint/lint_test.go

@@ -8,6 +8,7 @@ import (
 	"testing"
 
 	"sourcedock.dev/petrbalvin/gasm-devkit/arch"
+	"sourcedock.dev/petrbalvin/gasm-devkit/ast"
 	"sourcedock.dev/petrbalvin/gasm-devkit/parser"
 )
 
@@ -495,3 +496,33 @@ TEXT ·f(SB), NOSPLIT, $0
 		t.Fatalf("amd64 must not be flagged: %+v", diags)
 	}
 }
+
+// TestHasIndirectBranchShape checks that a JMP/CALL through a register or
+// memory suppresses reachability analysis, while a same-named label does not.
+func TestHasIndirectBranchShape(t *testing.T) {
+	tab := arch.ForArch(arch.AMD64)
+	indirect := `TEXT ·f(SB), NOSPLIT, $0
+	JMP AX
+	RET
+`
+	f, errs := parser.Parse("t_amd64.s", indirect)
+	if len(errs) > 0 {
+		t.Fatalf("parse: %v", errs)
+	}
+	if !hasIndirectBranch(f.Decls[0].(*ast.Text), tab) {
+		t.Error("JMP AX: indirect branch not detected")
+	}
+
+	label := `TEXT ·f(SB), NOSPLIT, $0
+loop:
+	JMP loop
+	RET
+`
+	f, errs = parser.Parse("t_amd64.s", label)
+	if len(errs) > 0 {
+		t.Fatalf("parse: %v", errs)
+	}
+	if hasIndirectBranch(f.Decls[0].(*ast.Text), tab) {
+		t.Error("JMP loop: label treated as an indirect branch")
+	}
+}