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//===-- ELFSymbols.cpp - ELF Symbol look-up functionality -------*- C++ -*-===//
//
// 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 "ELFSymbols.h"
using namespace llvm;
using namespace llvm::object;
using namespace llvm::ELF;
template <class ELFT>
static Expected<const typename ELFT::Sym *>
getSymbolFromGnuHashTable(StringRef Name, const typename ELFT::GnuHash &HashTab,
ArrayRef<typename ELFT::Sym> SymTab,
StringRef StrTab) {
const uint32_t NameHash = hashGnu(Name);
const typename ELFT::Word NBucket = HashTab.nbuckets;
const typename ELFT::Word SymOffset = HashTab.symndx;
ArrayRef<typename ELFT::Off> Filter = HashTab.filter();
ArrayRef<typename ELFT::Word> Bucket = HashTab.buckets();
ArrayRef<typename ELFT::Word> Chain = HashTab.values(SymTab.size());
// Check the bloom filter and exit early if the symbol is not present.
uint64_t ElfClassBits = ELFT::Is64Bits ? 64 : 32;
typename ELFT::Off Word =
Filter[(NameHash / ElfClassBits) % HashTab.maskwords];
uint64_t Mask = (0x1ull << (NameHash % ElfClassBits)) |
(0x1ull << ((NameHash >> HashTab.shift2) % ElfClassBits));
if ((Word & Mask) != Mask)
return nullptr;
// The symbol may or may not be present, check the hash values.
for (typename ELFT::Word I = Bucket[NameHash % NBucket];
I >= SymOffset && I < SymTab.size(); I = I + 1) {
const uint32_t ChainHash = Chain[I - SymOffset];
if ((NameHash | 0x1) != (ChainHash | 0x1))
continue;
if (SymTab[I].st_name >= StrTab.size())
return createError("symbol [index " + Twine(I) +
"] has invalid st_name: " + Twine(SymTab[I].st_name));
if (StrTab.drop_front(SymTab[I].st_name).data() == Name)
return &SymTab[I];
if (ChainHash & 0x1)
return nullptr;
}
return nullptr;
}
template <class ELFT>
static Expected<const typename ELFT::Sym *>
getSymbolFromSysVHashTable(StringRef Name, const typename ELFT::Hash &HashTab,
ArrayRef<typename ELFT::Sym> SymTab,
StringRef StrTab) {
const uint32_t Hash = hashSysV(Name);
const typename ELFT::Word NBucket = HashTab.nbucket;
ArrayRef<typename ELFT::Word> Bucket = HashTab.buckets();
ArrayRef<typename ELFT::Word> Chain = HashTab.chains();
for (typename ELFT::Word I = Bucket[Hash % NBucket]; I != ELF::STN_UNDEF;
I = Chain[I]) {
if (I >= SymTab.size())
return createError(
"symbol [index " + Twine(I) +
"] is greater than the number of symbols: " + Twine(SymTab.size()));
if (SymTab[I].st_name >= StrTab.size())
return createError("symbol [index " + Twine(I) +
"] has invalid st_name: " + Twine(SymTab[I].st_name));
if (StrTab.drop_front(SymTab[I].st_name).data() == Name)
return &SymTab[I];
}
return nullptr;
}
template <class ELFT>
static Expected<const typename ELFT::Sym *>
getHashTableSymbol(const ELFFile<ELFT> &Elf, const typename ELFT::Shdr &Sec,
StringRef Name) {
if (Sec.sh_type != ELF::SHT_HASH && Sec.sh_type != ELF::SHT_GNU_HASH)
return createError(
"invalid sh_type for hash table, expected SHT_HASH or SHT_GNU_HASH");
Expected<typename ELFT::ShdrRange> SectionsOrError = Elf.sections();
if (!SectionsOrError)
return SectionsOrError.takeError();
auto SymTabOrErr = getSection<ELFT>(*SectionsOrError, Sec.sh_link);
if (!SymTabOrErr)
return SymTabOrErr.takeError();
auto StrTabOrErr =
Elf.getStringTableForSymtab(**SymTabOrErr, *SectionsOrError);
if (!StrTabOrErr)
return StrTabOrErr.takeError();
StringRef StrTab = *StrTabOrErr;
auto SymsOrErr = Elf.symbols(*SymTabOrErr);
if (!SymsOrErr)
return SymsOrErr.takeError();
ArrayRef<typename ELFT::Sym> SymTab = *SymsOrErr;
// If this is a GNU hash table we verify its size and search the symbol
// table using the GNU hash table format.
if (Sec.sh_type == ELF::SHT_GNU_HASH) {
const typename ELFT::GnuHash *HashTab =
reinterpret_cast<const typename ELFT::GnuHash *>(Elf.base() +
Sec.sh_offset);
if (Sec.sh_offset + Sec.sh_size >= Elf.getBufSize())
return createError("section has invalid sh_offset: " +
Twine(Sec.sh_offset));
if (Sec.sh_size < sizeof(typename ELFT::GnuHash) ||
Sec.sh_size <
sizeof(typename ELFT::GnuHash) +
sizeof(typename ELFT::Word) * HashTab->maskwords +
sizeof(typename ELFT::Word) * HashTab->nbuckets +
sizeof(typename ELFT::Word) * (SymTab.size() - HashTab->symndx))
return createError("section has invalid sh_size: " + Twine(Sec.sh_size));
return getSymbolFromGnuHashTable<ELFT>(Name, *HashTab, SymTab, StrTab);
}
// If this is a Sys-V hash table we verify its size and search the symbol
// table using the Sys-V hash table format.
if (Sec.sh_type == ELF::SHT_HASH) {
const typename ELFT::Hash *HashTab =
reinterpret_cast<const typename ELFT::Hash *>(Elf.base() +
Sec.sh_offset);
if (Sec.sh_offset + Sec.sh_size >= Elf.getBufSize())
return createError("section has invalid sh_offset: " +
Twine(Sec.sh_offset));
if (Sec.sh_size < sizeof(typename ELFT::Hash) ||
Sec.sh_size < sizeof(typename ELFT::Hash) +
sizeof(typename ELFT::Word) * HashTab->nbucket +
sizeof(typename ELFT::Word) * HashTab->nchain)
return createError("section has invalid sh_size: " + Twine(Sec.sh_size));
return getSymbolFromSysVHashTable<ELFT>(Name, *HashTab, SymTab, StrTab);
}
return nullptr;
}
template <class ELFT>
static Expected<const typename ELFT::Sym *>
getSymTableSymbol(const ELFFile<ELFT> &Elf, const typename ELFT::Shdr &Sec,
StringRef Name) {
if (Sec.sh_type != ELF::SHT_SYMTAB && Sec.sh_type != ELF::SHT_DYNSYM)
return createError(
"invalid sh_type for hash table, expected SHT_SYMTAB or SHT_DYNSYM");
Expected<typename ELFT::ShdrRange> SectionsOrError = Elf.sections();
if (!SectionsOrError)
return SectionsOrError.takeError();
auto StrTabOrErr = Elf.getStringTableForSymtab(Sec, *SectionsOrError);
if (!StrTabOrErr)
return StrTabOrErr.takeError();
StringRef StrTab = *StrTabOrErr;
auto SymsOrErr = Elf.symbols(&Sec);
if (!SymsOrErr)
return SymsOrErr.takeError();
ArrayRef<typename ELFT::Sym> SymTab = *SymsOrErr;
for (const typename ELFT::Sym &Sym : SymTab)
if (StrTab.drop_front(Sym.st_name).data() == Name)
return &Sym;
return nullptr;
}
Expected<const typename ELF64LE::Sym *>
getELFSymbol(const ELFObjectFile<ELF64LE> &ELFObj, StringRef Name) {
// First try to look up the symbol via the hash table.
for (ELFSectionRef Sec : ELFObj.sections()) {
if (Sec.getType() != SHT_HASH && Sec.getType() != SHT_GNU_HASH)
continue;
auto HashTabOrErr = ELFObj.getELFFile().getSection(Sec.getIndex());
if (!HashTabOrErr)
return HashTabOrErr.takeError();
return getHashTableSymbol<ELF64LE>(ELFObj.getELFFile(), **HashTabOrErr,
Name);
}
// If this is an executable file check the entire standard symbol table.
for (ELFSectionRef Sec : ELFObj.sections()) {
if (Sec.getType() != SHT_SYMTAB)
continue;
auto SymTabOrErr = ELFObj.getELFFile().getSection(Sec.getIndex());
if (!SymTabOrErr)
return SymTabOrErr.takeError();
return getSymTableSymbol<ELF64LE>(ELFObj.getELFFile(), **SymTabOrErr, Name);
}
return nullptr;
}
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