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[ELF] Simplify GnuHashSection::write. NFC

This commit is contained in:
Fangrui Song 2021-11-25 14:23:25 -08:00
parent 55c14d6dbf
commit 5ca54c6686
2 changed files with 4 additions and 20 deletions
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21
lld/ELF/SyntheticSections.cpp
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@ -2380,21 +2380,8 @@ void GnuHashTableSection::writeTo(uint8_t *buf) {
write32(buf + 12, Shift2); write32(buf + 12, Shift2);
buf += 16; buf += 16;
// Write a bloom filter and a hash table. // Write the 2-bit bloom filter.
writeBloomFilter(buf); const unsigned c = config->is64 ? 64 : 32;
buf += config->wordsize * maskWords;
writeHashTable(buf);
}
// This function writes a 2-bit bloom filter. This bloom filter alone
// usually filters out 80% or more of all symbol lookups [1].
// The dynamic linker uses the hash table only when a symbol is not
// filtered out by a bloom filter.
//
// [1] Ulrich Drepper (2011), "How To Write Shared Libraries" (Ver. 4.1.2),
// p.9, https://www.akkadia.org/drepper/dsohowto.pdf
void GnuHashTableSection::writeBloomFilter(uint8_t *buf) {
unsigned c = config->is64 ? 64 : 32;
for (const Entry &sym : symbols) { for (const Entry &sym : symbols) {
// When C = 64, we choose a word with bits [6:...] and set 1 to two bits in // When C = 64, we choose a word with bits [6:...] and set 1 to two bits in
// the word using bits [0:5] and [26:31]. // the word using bits [0:5] and [26:31].
@ -2404,9 +2391,9 @@ void GnuHashTableSection::writeBloomFilter(uint8_t *buf) {
val |= uint64_t(1) << ((sym.hash >> Shift2) % c); val |= uint64_t(1) << ((sym.hash >> Shift2) % c);
writeUint(buf + i * config->wordsize, val); writeUint(buf + i * config->wordsize, val);
} }
} buf += config->wordsize * maskWords;
void GnuHashTableSection::writeHashTable(uint8_t *buf) { // Write the hash table.
uint32_t *buckets = reinterpret_cast<uint32_t *>(buf); uint32_t *buckets = reinterpret_cast<uint32_t *>(buf);
uint32_t oldBucket = -1; uint32_t oldBucket = -1;
uint32_t *values = buckets + nBuckets; uint32_t *values = buckets + nBuckets;

3
lld/ELF/SyntheticSections.h
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@ -675,9 +675,6 @@ private:
// See the comment in writeBloomFilter. // See the comment in writeBloomFilter.
enum { Shift2 = 26 }; enum { Shift2 = 26 };
void writeBloomFilter(uint8_t *buf);
void writeHashTable(uint8_t *buf);
struct Entry { struct Entry {
Symbol *sym; Symbol *sym;
size_t strTabOffset; size_t strTabOffset;