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//===--- HeaderMap.cpp - A file that acts like dir of symlinks ------------===//
// The LLVM Compiler Infrastructure
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
// This file implements the HeaderMap interface.
#include "clang/Lex/HeaderMap.h"
#include "clang/Basic/CharInfo.h"
#include "clang/Basic/FileManager.h"
#include "llvm/ADT/SmallString.h"
#include "llvm/Support/DataTypes.h"
#include "llvm/Support/MathExtras.h"
#include "llvm/Support/MemoryBuffer.h"
#include <cstdio>
#include <memory>
using namespace clang;
// Data Structures and Manifest Constants
enum {
HMAP_HeaderMagicNumber = ('h' << 24) | ('m' << 16) | ('a' << 8) | 'p',
HMAP_HeaderVersion = 1,
HMAP_EmptyBucketKey = 0
namespace clang {
struct HMapBucket {
uint32_t Key; // Offset (into strings) of key.
uint32_t Prefix; // Offset (into strings) of value prefix.
uint32_t Suffix; // Offset (into strings) of value suffix.
struct HMapHeader {
uint32_t Magic; // Magic word, also indicates byte order.
uint16_t Version; // Version number -- currently 1.
uint16_t Reserved; // Reserved for future use - zero for now.
uint32_t StringsOffset; // Offset to start of string pool.
uint32_t NumEntries; // Number of entries in the string table.
uint32_t NumBuckets; // Number of buckets (always a power of 2).
uint32_t MaxValueLength; // Length of longest result path (excluding nul).
// An array of 'NumBuckets' HMapBucket objects follows this header.
// Strings follow the buckets, at StringsOffset.
} // end namespace clang.
/// HashHMapKey - This is the 'well known' hash function required by the file
/// format, used to look up keys in the hash table. The hash table uses simple
/// linear probing based on this function.
static inline unsigned HashHMapKey(StringRef Str) {
unsigned Result = 0;
const char *S = Str.begin(), *End = Str.end();
for (; S != End; S++)
Result += toLowercase(*S) * 13;
return Result;
// Verification and Construction
/// HeaderMap::Create - This attempts to load the specified file as a header
/// map. If it doesn't look like a HeaderMap, it gives up and returns null.
/// If it looks like a HeaderMap but is obviously corrupted, it puts a reason
/// into the string error argument and returns null.
const HeaderMap *HeaderMap::Create(const FileEntry *FE, FileManager &FM) {
// If the file is too small to be a header map, ignore it.
unsigned FileSize = FE->getSize();
if (FileSize <= sizeof(HMapHeader)) return nullptr;
auto FileBuffer = FM.getBufferForFile(FE);
if (!FileBuffer) return nullptr; // Unreadable file?
const char *FileStart = (*FileBuffer)->getBufferStart();
// We know the file is at least as big as the header, check it now.
const HMapHeader *Header = reinterpret_cast<const HMapHeader*>(FileStart);
// Sniff it to see if it's a headermap by checking the magic number and
// version.
bool NeedsByteSwap;
if (Header->Magic == HMAP_HeaderMagicNumber &&
Header->Version == HMAP_HeaderVersion)
NeedsByteSwap = false;
else if (Header->Magic == llvm::ByteSwap_32(HMAP_HeaderMagicNumber) &&
Header->Version == llvm::ByteSwap_16(HMAP_HeaderVersion))
NeedsByteSwap = true; // Mixed endianness headermap.
return nullptr; // Not a header map.
if (Header->Reserved != 0) return nullptr;
// Okay, everything looks good, create the header map.
return new HeaderMap(std::move(*FileBuffer), NeedsByteSwap);
// Utility Methods
/// getFileName - Return the filename of the headermap.
const char *HeaderMap::getFileName() const {
return FileBuffer->getBufferIdentifier();
unsigned HeaderMap::getEndianAdjustedWord(unsigned X) const {
if (!NeedsBSwap) return X;
return llvm::ByteSwap_32(X);
/// getHeader - Return a reference to the file header, in unbyte-swapped form.
/// This method cannot fail.
const HMapHeader &HeaderMap::getHeader() const {
// We know the file is at least as big as the header. Return it.
return *reinterpret_cast<const HMapHeader*>(FileBuffer->getBufferStart());
/// getBucket - Return the specified hash table bucket from the header map,
/// bswap'ing its fields as appropriate. If the bucket number is not valid,
/// this return a bucket with an empty key (0).
HMapBucket HeaderMap::getBucket(unsigned BucketNo) const {
HMapBucket Result;
Result.Key = HMAP_EmptyBucketKey;
const HMapBucket *BucketArray =
reinterpret_cast<const HMapBucket*>(FileBuffer->getBufferStart() +
const HMapBucket *BucketPtr = BucketArray+BucketNo;
if ((const char*)(BucketPtr+1) > FileBuffer->getBufferEnd()) {
Result.Prefix = 0;
Result.Suffix = 0;
return Result; // Invalid buffer, corrupt hmap.
// Otherwise, the bucket is valid. Load the values, bswapping as needed.
Result.Key = getEndianAdjustedWord(BucketPtr->Key);
Result.Prefix = getEndianAdjustedWord(BucketPtr->Prefix);
Result.Suffix = getEndianAdjustedWord(BucketPtr->Suffix);
return Result;
/// getString - Look up the specified string in the string table. If the string
/// index is not valid, it returns an empty string.
const char *HeaderMap::getString(unsigned StrTabIdx) const {
// Add the start of the string table to the idx.
StrTabIdx += getEndianAdjustedWord(getHeader().StringsOffset);
// Check for invalid index.
if (StrTabIdx >= FileBuffer->getBufferSize())
return nullptr;
// Otherwise, we have a valid pointer into the file. Just return it. We know
// that the "string" can not overrun the end of the file, because the buffer
// is nul terminated by virtue of being a MemoryBuffer.
return FileBuffer->getBufferStart()+StrTabIdx;
// The Main Drivers
/// dump - Print the contents of this headermap to stderr.
void HeaderMap::dump() const {
const HMapHeader &Hdr = getHeader();
unsigned NumBuckets = getEndianAdjustedWord(Hdr.NumBuckets);
fprintf(stderr, "Header Map %s:\n %d buckets, %d entries\n",
getFileName(), NumBuckets,
for (unsigned i = 0; i != NumBuckets; ++i) {
HMapBucket B = getBucket(i);
if (B.Key == HMAP_EmptyBucketKey) continue;
const char *Key = getString(B.Key);
const char *Prefix = getString(B.Prefix);
const char *Suffix = getString(B.Suffix);
fprintf(stderr, " %d. %s -> '%s' '%s'\n", i, Key, Prefix, Suffix);
/// LookupFile - Check to see if the specified relative filename is located in
/// this HeaderMap. If so, open it and return its FileEntry.
const FileEntry *HeaderMap::LookupFile(
StringRef Filename, FileManager &FM) const {
SmallString<1024> Path;
StringRef Dest = lookupFilename(Filename, Path);
if (Dest.empty())
return nullptr;
return FM.getFile(Dest);
StringRef HeaderMap::lookupFilename(StringRef Filename,
SmallVectorImpl<char> &DestPath) const {
const HMapHeader &Hdr = getHeader();
unsigned NumBuckets = getEndianAdjustedWord(Hdr.NumBuckets);
// If the number of buckets is not a power of two, the headermap is corrupt.
// Don't probe infinitely.
if (NumBuckets & (NumBuckets-1))
return StringRef();
// Linearly probe the hash table.
for (unsigned Bucket = HashHMapKey(Filename);; ++Bucket) {
HMapBucket B = getBucket(Bucket & (NumBuckets-1));
if (B.Key == HMAP_EmptyBucketKey) return StringRef(); // Hash miss.
// See if the key matches. If not, probe on.
if (!Filename.equals_lower(getString(B.Key)))
// If so, we have a match in the hash table. Construct the destination
// path.
StringRef Prefix = getString(B.Prefix);
StringRef Suffix = getString(B.Suffix);
DestPath.append(Prefix.begin(), Prefix.end());
DestPath.append(Suffix.begin(), Suffix.end());
return StringRef(DestPath.begin(), DestPath.size());