gasm-sdk/parser/flags.go

// Copyright (c) 2026 Petr Balvín <opensource@petrbalvin.org> (https://petrbalvin.org)
// SPDX-License-Identifier: BSD-3-Clause

// The TEXT and GLOBL flags operand.
//
// The toolchain reads the middle operand of a TEXT (and of a GLOBL) as one
// constant expression: identifiers joined by '|', each a name
// runtime/textflag.h defines as a number, with literals and constant
// arithmetic beside them (cmd/asm/internal/asm/asm.go, evalInteger).  gasm
// consumes textflag.h natively rather than expanding it, so the names are
// evaluated here against the same table, and an identifier outside it is
// the toolchain's evaluation failure.
package parser

import (
	"strconv"

	"sourcedock.dev/petrbalvin/gasm-sdk/token"
)

// textFlags is the flag table of runtime/textflag.h: the names the
// assembler knows and the values they stand for.
var textFlags = map[string]int64{
	"NOPROF":        1,
	"DUPOK":         2,
	"NOSPLIT":       4,
	"RODATA":        8,
	"NOPTR":         16,
	"WRAPPER":       32,
	"NEEDCTXT":      64,
	"TLSBSS":        256,
	"NOFRAME":       512,
	"REFLECTMETHOD": 1024,
	"TOPFRAME":      2048,
	"ABIWRAPPER":    4096,
}

// flagNOSPLIT and flagNOFRAME single out the two flags whose value the
// parser itself reasons about, in the toolchain's own TEXT diagnostics.
const (
	flagNOSPLIT = 4
	flagNOFRAME = 512
)

// flagOrder lists the table ascending by value, the order the canonical
// name expansion of a folded value reads in.
var flagOrder = []struct {
	name string
	val  int64
}{
	{"NOPROF", 1},
	{"DUPOK", 2},
	{"NOSPLIT", 4},
	{"RODATA", 8},
	{"NOPTR", 16},
	{"WRAPPER", 32},
	{"NEEDCTXT", 64},
	{"TLSBSS", 256},
	{"NOFRAME", 512},
	{"REFLECTMETHOD", 1024},
	{"TOPFRAME", 2048},
	{"ABIWRAPPER", 4096},
}

// flagsRun strips the comments from one flags operand.  A comment on a
// directive line is always its trailing text (a comment mid-line is the
// statement boundary the statement reader makes of it), so what the
// operand split hands over carries it at the tail at most.
func flagsRun(g []token.Token) []token.Token {
	out := make([]token.Token, 0, len(g))
	for _, t := range g {
		if t.Kind != token.Comment {
			out = append(out, t)
		}
	}
	return out
}

// evalFlags evaluates one flags operand.  Every identifier must name a
// flag in textFlags; the toolchain rejects any other with "unexpected NAME
// evaluating expression", and so does this.  The whole operand folds to
// one integer, which is returned as the value.  pseudo names the directive
// in the toolchain's own diagnostics ("TEXT", "GLOBL").
//
// The names returned follow the operand's own spelling: an operand written
// purely as names keeps them in written order, duplicates included, the
// toolchain accepting both silently; an operand that mixes in literals or
// arithmetic has no written names to keep, so the folded value expands to
// the canonical ascending name list.  Bits outside the table (a literal
// such as 8192) live in the value alone; the names cannot spell them.
//
// After a failure the names collected so far are returned with value 0:
// the tree stays usable beside the diagnostic, and value 0 is exactly the
// flags the assembler can trust the operand for.
func (p *state) evalFlags(g []token.Token, keepWritten bool, pseudo string) ([]string, int64) {
	if len(g) == 0 {
		return nil, 0
	}
	// The flags operand is a bare constant expression; the immediate
	// spelling is the toolchain's "TEXT: expected integer constant".
	if g[0].Kind == token.Dollar {
		if p.expand {
			found := "$"
			if len(g) > 1 {
				found += g[1].Text
			}
			p.errorf(g[0].Pos, "%s: expected integer constant; found %s", pseudo, found)
		}
		return nil, 0
	}

	sub := make([]token.Token, 0, len(g))
	var names []string
	namesOnly := true
	failed := false
	for _, t := range g {
		if t.Kind == token.Ident {
			v, ok := textFlags[t.Text]
			if !ok {
				if p.expand {
					p.errorf(t.Pos, "unexpected %s evaluating expression", t.Text)
				}
				failed = true
			}
			names = append(names, t.Text)
			if ok {
				sub = append(sub, numberToken(v, t))
			}
			continue
		}
		if t.Kind != token.Pipe {
			// Anything beyond names and their '|' separators gives the
			// operand arithmetic the written names cannot express.
			namesOnly = false
		}
		if keepWritten && t.Kind == token.Number {
			names = append(names, t.Text)
		}
		sub = append(sub, t)
	}
	if failed {
		return names, 0
	}
	v, rest, ok := foldExpr(sub)
	if !ok || len(rest) > 0 {
		if p.expand {
			bad := g[0]
			if ok && len(rest) > 0 {
				bad = rest[0]
			}
			p.errorf(bad.Pos, "unexpected %s evaluating expression", bad.Text)
		}
		return names, 0
	}
	if keepWritten {
		return names, v
	}
	if namesOnly {
		// Written names stay exactly as written; the value folds them.
		return names, v
	}
	return flagNames(v), v
}

// flagNames expands a folded flags value into the canonical ascending name
// list of the table's bits it holds.  A negative value expands to nothing:
// its bit pattern is not a combination the names can spell.
func flagNames(v int64) []string {
	if v <= 0 {
		return nil
	}
	var out []string
	for _, f := range flagOrder {
		if v&f.val != 0 {
			out = append(out, f.name)
			v &^= f.val
		}
	}
	return out
}

// numberToken rebuilds t as the decimal literal of v at t's position.
func numberToken(v int64, t token.Token) token.Token {
	return token.Token{Kind: token.Number, Text: strconv.FormatInt(v, 10), Pos: t.Pos, End: t.End}
}