//===- lib/MC/MCWasmStreamer.cpp - Wasm Object Output ---------------------===//
//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See https://llvm.org/LICENSE.txt for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
//
//===----------------------------------------------------------------------===//
//
// This file assembles .s files and emits Wasm .o object files.
//
//===----------------------------------------------------------------------===//

#include "llvm/MC/MCWasmStreamer.h"
#include "llvm/MC/MCAsmBackend.h"
#include "llvm/MC/MCAssembler.h"
#include "llvm/MC/MCCodeEmitter.h"
#include "llvm/MC/MCContext.h"
#include "llvm/MC/MCExpr.h"
#include "llvm/MC/MCFixup.h"
#include "llvm/MC/MCObjectStreamer.h"
#include "llvm/MC/MCSection.h"
#include "llvm/MC/MCSectionWasm.h"
#include "llvm/MC/MCSymbol.h"
#include "llvm/MC/MCSymbolWasm.h"
#include "llvm/MC/SectionKind.h"
#include "llvm/MC/TargetRegistry.h"
#include "llvm/Support/Alignment.h"
#include "llvm/Support/ErrorHandling.h"
#include "llvm/Support/MathExtras.h"

namespace llvm {
class MCContext;
class MCStreamer;
class MCSubtargetInfo;
} // namespace llvm

using namespace llvm;

MCWasmStreamer::~MCWasmStreamer() = default; // anchor.

void MCWasmStreamer::emitLabel(MCSymbol *S, SMLoc Loc) {
  auto *Symbol = static_cast<MCSymbolWasm *>(S);
  MCObjectStreamer::emitLabel(Symbol, Loc);

  const MCSectionWasm &Section =
      static_cast<const MCSectionWasm &>(*getCurrentSectionOnly());
  if (Section.getSegmentFlags() & wasm::WASM_SEG_FLAG_TLS)
    Symbol->setTLS();
}

void MCWasmStreamer::emitLabelAtPos(MCSymbol *S, SMLoc Loc, MCFragment &F,
                                    uint64_t Offset) {
  auto *Symbol = static_cast<MCSymbolWasm *>(S);
  MCObjectStreamer::emitLabelAtPos(Symbol, Loc, F, Offset);

  const MCSectionWasm &Section =
      static_cast<const MCSectionWasm &>(*getCurrentSectionOnly());
  if (Section.getSegmentFlags() & wasm::WASM_SEG_FLAG_TLS)
    Symbol->setTLS();
}

void MCWasmStreamer::emitAssignment(MCSymbol *S, const MCExpr *Value) {
  auto *Symbol = static_cast<MCSymbolWasm *>(S);

  // wasm has no absolute addressing. A symbol assigned a bare integer constant
  // ("sym = N" / ".set sym, N", with no symbol reference) cannot be modeled as
  // an absolute symbol: WasmObjectWriter's alias pass calls getBaseSymbol(),
  // which is null for a pure constant, and previously aborted MC finalization
  // with "absolute addressing not supported". glibc emits exactly this for
  // address-taken linkage markers (e.g. _nl_current_LC_*_used from
  // _NL_CURRENT_DEFINE in locale/localeinfo.h), where the symbol's *address* is
  // taken to force a translation unit to be linked, and any read of the symbol
  // is expected to yield the constant.
  //
  // Lower a named (non-temporary) absolute-constant symbol to a real defined
  // data object that holds the constant in its own data section. It then has a
  // genuine wasm linear-memory address that can be taken and relocated at link
  // (resolving an undefined reference in another object), and a load of it
  // yields the constant. This mirrors what GNU-as effectively provides for the
  // construct on ELF (a defined symbol with an address). It is never-silent:
  // the address is real, the value is preserved, and nothing is dropped.
  //
  // Assignments that reference other symbols (true aliases, label differences)
  // are left to the normal assembler-alias machinery (the WasmObjectWriter
  // alias pass and the prior alias-to-undefined / .symver fixes). Temporary,
  // assembler-internal absolute constants are also left as plain assignments:
  // they are folded into immediates at encode time and never need an address.
  int64_t Const;
  if (!Symbol->isTemporary() && Value->evaluateAsAbsolute(Const)) {
    MCContext &Ctx = getContext();

    // Store the constant in the target pointer width, widened only if needed so
    // the stored bytes equal the constant exactly (no silent truncation).
    unsigned Width = Ctx.getTargetTriple().isArch64Bit() ? 8 : 4;
    while (Width < 8 && !isIntN(Width * 8, Const) &&
           !isUIntN(Width * 8, static_cast<uint64_t>(Const)))
      Width *= 2;

    // A dedicated data section so the marker is independently addressable and
    // garbage-collectable, exactly like any other defined data symbol.
    MCSection *DataSec = Ctx.getWasmSection(Twine(".data.") + Symbol->getName(),
                                            SectionKind::getData());

    MCSection *Prev = getCurrentSectionOnly();
    switchSection(DataSec);
    emitValueToAlignment(Align(Width));
    emitLabel(Symbol);
    emitIntValue(static_cast<uint64_t>(Const), Width);
    Symbol->setSize(MCConstantExpr::create(Width, Ctx));
    // Record the constant so a repeated, identical "sym = N" (which glibc emits
    // per-TU and llvm-link concatenates without dedup) is recognized in the
    // parser as an idempotent no-op rather than colliding as a redefinition of
    // this now-defined data label, while a repeat to a *different* constant is
    // still rejected loudly. See MCParserUtils::parseAssignmentExpression.
    Symbol->setAbsoluteConstant(Const);
    if (Prev)
      switchSection(Prev);
    return;
  }

  MCObjectStreamer::emitAssignment(S, Value);
}

void MCWasmStreamer::changeSection(MCSection *Section, uint32_t Subsection) {
  MCAssembler &Asm = getAssembler();
  auto *SectionWasm = static_cast<const MCSectionWasm *>(Section);
  const MCSymbol *Grp = SectionWasm->getGroup();
  if (Grp)
    Asm.registerSymbol(*Grp);

  this->MCObjectStreamer::changeSection(Section, Subsection);
  Asm.registerSymbol(*Section->getBeginSymbol());
}

bool MCWasmStreamer::emitSymbolAttribute(MCSymbol *S, MCSymbolAttr Attribute) {
  assert(Attribute != MCSA_IndirectSymbol && "indirect symbols not supported");
  auto *Symbol = static_cast<MCSymbolWasm *>(S);

  // Adding a symbol attribute always introduces the symbol; note that an
  // important side effect of calling registerSymbol here is to register the
  // symbol with the assembler.
  getAssembler().registerSymbol(*Symbol);

  switch (Attribute) {
  case MCSA_LazyReference:
  case MCSA_Reference:
  case MCSA_SymbolResolver:
  case MCSA_PrivateExtern:
  case MCSA_WeakDefinition:
  case MCSA_WeakDefAutoPrivate:
  case MCSA_Invalid:
  case MCSA_IndirectSymbol:
  case MCSA_Protected:
  case MCSA_Exported:
    return false;

  case MCSA_Hidden:
    Symbol->setHidden(true);
    break;

  case MCSA_Weak:
  case MCSA_WeakReference:
    Symbol->setWeak(true);
    Symbol->setExternal(true);
    break;

  case MCSA_Global:
    Symbol->setExternal(true);
    break;

  case MCSA_ELF_TypeFunction:
    Symbol->setType(wasm::WASM_SYMBOL_TYPE_FUNCTION);
    break;

  case MCSA_ELF_TypeTLS:
    Symbol->setTLS();
    break;

  case MCSA_ELF_TypeObject:
  case MCSA_Cold:
    break;

  case MCSA_NoDeadStrip:
    Symbol->setNoStrip();
    break;

  default:
    // unrecognized directive
    llvm_unreachable("unexpected MCSymbolAttr");
    return false;
  }

  return true;
}

void MCWasmStreamer::emitCommonSymbol(MCSymbol *S, uint64_t Size,
                                      Align ByteAlignment) {
  llvm_unreachable("Common symbols are not yet implemented for Wasm");
}

void MCWasmStreamer::emitELFSize(MCSymbol *Symbol, const MCExpr *Value) {
  static_cast<MCSymbolWasm *>(Symbol)->setSize(Value);
}

void MCWasmStreamer::emitLocalCommonSymbol(MCSymbol *S, uint64_t Size,
                                           Align ByteAlignment) {
  llvm_unreachable("Local common symbols are not yet implemented for Wasm");
}

void MCWasmStreamer::emitIdent(StringRef IdentString) {
  // TODO(sbc): Add the ident section once we support mergable strings
  // sections in the object format
}

void MCWasmStreamer::finishImpl() {
  emitFrames();

  this->MCObjectStreamer::finishImpl();
}

MCStreamer *llvm::createWasmStreamer(MCContext &Context,
                                     std::unique_ptr<MCAsmBackend> &&MAB,
                                     std::unique_ptr<MCObjectWriter> &&OW,
                                     std::unique_ptr<MCCodeEmitter> &&CE) {
  MCWasmStreamer *S =
      new MCWasmStreamer(Context, std::move(MAB), std::move(OW), std::move(CE));
  return S;
}