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//===- StringTableBuilder.cpp - String table building utility -------------===//
//
// 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
//
//===----------------------------------------------------------------------===//
#include "llvm/MC/StringTableBuilder.h"
#include "llvm/ADT/ArrayRef.h"
#include "llvm/ADT/CachedHashString.h"
#include "llvm/ADT/SmallString.h"
#include "llvm/ADT/StringRef.h"
#include "llvm/BinaryFormat/COFF.h"
#include "llvm/Support/Endian.h"
#include "llvm/Support/MathExtras.h"
#include "llvm/Support/raw_ostream.h"
#include <cassert>
#include <cstddef>
#include <cstdint>
#include <cstring>
#include <utility>
#include <vector>
using namespace llvm;
StringTableBuilder::~StringTableBuilder() = default;
void StringTableBuilder::initSize() {
// Account for leading bytes in table so that offsets returned from add are
// correct.
switch (K) {
case RAW:
case DWARF:
Size = 0;
break;
case MachOLinked:
case MachO64Linked:
Size = 2;
break;
case MachO:
case MachO64:
case ELF:
// Start the table with a NUL byte.
Size = 1;
break;
case XCOFF:
case WinCOFF:
// Make room to write the table size later.
Size = 4;
break;
}
}
StringTableBuilder::StringTableBuilder(Kind K, unsigned Alignment)
: K(K), Alignment(Alignment) {
initSize();
}
void StringTableBuilder::write(raw_ostream &OS) const {
assert(isFinalized());
SmallString<0> Data;
Data.resize(getSize());
write((uint8_t *)Data.data());
OS << Data;
}
using StringPair = std::pair<CachedHashStringRef, size_t>;
void StringTableBuilder::write(uint8_t *Buf) const {
assert(isFinalized());
for (const StringPair &P : StringIndexMap) {
StringRef Data = P.first.val();
if (!Data.empty())
memcpy(Buf + P.second, Data.data(), Data.size());
}
// The COFF formats store the size of the string table in the first 4 bytes.
// For Windows, the format is little-endian; for AIX, it is big-endian.
if (K == WinCOFF)
support::endian::write32le(Buf, Size);
else if (K == XCOFF)
support::endian::write32be(Buf, Size);
}
// Returns the character at Pos from end of a string.
static int charTailAt(StringPair *P, size_t Pos) {
StringRef S = P->first.val();
if (Pos >= S.size())
return -1;
return (unsigned char)S[S.size() - Pos - 1];
}
// Three-way radix quicksort. This is much faster than std::sort with strcmp
// because it does not compare characters that we already know the same.
static void multikeySort(MutableArrayRef<StringPair *> Vec, int Pos) {
tailcall:
if (Vec.size() <= 1)
return;
// Partition items so that items in [0, I) are greater than the pivot,
// [I, J) are the same as the pivot, and [J, Vec.size()) are less than
// the pivot.
int Pivot = charTailAt(Vec[0], Pos);
size_t I = 0;
size_t J = Vec.size();
for (size_t K = 1; K < J;) {
int C = charTailAt(Vec[K], Pos);
if (C > Pivot)
std::swap(Vec[I++], Vec[K++]);
else if (C < Pivot)
std::swap(Vec[--J], Vec[K]);
else
K++;
}
multikeySort(Vec.slice(0, I), Pos);
multikeySort(Vec.slice(J), Pos);
// multikeySort(Vec.slice(I, J - I), Pos + 1), but with
// tail call optimization.
if (Pivot != -1) {
Vec = Vec.slice(I, J - I);
++Pos;
goto tailcall;
}
}
void StringTableBuilder::finalize() {
assert(K != DWARF);
finalizeStringTable(/*Optimize=*/true);
}
void StringTableBuilder::finalizeInOrder() {
finalizeStringTable(/*Optimize=*/false);
}
void StringTableBuilder::finalizeStringTable(bool Optimize) {
Finalized = true;
if (Optimize) {
std::vector<StringPair *> Strings;
Strings.reserve(StringIndexMap.size());
for (StringPair &P : StringIndexMap)
Strings.push_back(&P);
multikeySort(Strings, 0);
initSize();
StringRef Previous;
for (StringPair *P : Strings) {
StringRef S = P->first.val();
if (Previous.endswith(S)) {
size_t Pos = Size - S.size() - (K != RAW);
if (!(Pos & (Alignment - 1))) {
P->second = Pos;
continue;
}
}
Size = alignTo(Size, Alignment);
P->second = Size;
Size += S.size();
if (K != RAW)
++Size;
Previous = S;
}
}
if (K == MachO || K == MachOLinked)
Size = alignTo(Size, 4); // Pad to multiple of 4.
if (K == MachO64 || K == MachO64Linked)
Size = alignTo(Size, 8); // Pad to multiple of 8.
// According to ld64 the string table of a final linked Mach-O binary starts
// with " ", i.e. the first byte is ' ' and the second byte is zero. In
// 'initSize()' we reserved the first two bytes for holding this string.
if (K == MachOLinked || K == MachO64Linked)
StringIndexMap[CachedHashStringRef(" ")] = 0;
// The first byte in an ELF string table must be null, according to the ELF
// specification. In 'initSize()' we reserved the first byte to hold null for
// this purpose and here we actually add the string to allow 'getOffset()' to
// be called on an empty string.
if (K == ELF)
StringIndexMap[CachedHashStringRef("")] = 0;
}
void StringTableBuilder::clear() {
Finalized = false;
StringIndexMap.clear();
}
size_t StringTableBuilder::getOffset(CachedHashStringRef S) const {
assert(isFinalized());
auto I = StringIndexMap.find(S);
assert(I != StringIndexMap.end() && "String is not in table!");
return I->second;
}
size_t StringTableBuilder::add(CachedHashStringRef S) {
if (K == WinCOFF)
assert(S.size() > COFF::NameSize && "Short string in COFF string table!");
assert(!isFinalized());
auto P = StringIndexMap.insert(std::make_pair(S, 0));
if (P.second) {
size_t Start = alignTo(Size, Alignment);
P.first->second = Start;
Size = Start + S.size() + (K != RAW);
}
return P.first->second;
}
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