[lld] r328579 - Refactor SharedFile::parseRest. NFC.
Rui Ueyama via llvm-commits
llvm-commits at lists.llvm.org
Mon Mar 26 12:57:38 PDT 2018
Author: ruiu
Date: Mon Mar 26 12:57:38 2018
New Revision: 328579
URL: http://llvm.org/viewvc/llvm-project?rev=328579&view=rev
Log:
Refactor SharedFile::parseRest. NFC.
SharedFile::parseRest function grew organically and got a bit hard to
understand. This patch refactor it. This patch also adds comments.
Differential Revision: https://reviews.llvm.org/D44860
Modified:
lld/trunk/ELF/InputFiles.cpp
lld/trunk/ELF/InputFiles.h
Modified: lld/trunk/ELF/InputFiles.cpp
URL: http://llvm.org/viewvc/llvm-project/lld/trunk/ELF/InputFiles.cpp?rev=328579&r1=328578&r2=328579&view=diff
==============================================================================
--- lld/trunk/ELF/InputFiles.cpp (original)
+++ lld/trunk/ELF/InputFiles.cpp Mon Mar 26 12:57:38 2018
@@ -782,23 +782,32 @@ template <class ELFT> void SharedFile<EL
}
}
+// Parses ".gnu.version" section which is a parallel array for the symbol table.
+// If a given file doesn't have ".gnu.version" section, returns VER_NDX_GLOBAL.
+template <class ELFT> std::vector<uint32_t> SharedFile<ELFT>::parseVersyms() {
+ size_t Size = this->ELFSyms.size() - this->FirstNonLocal;
+ if (!VersymSec)
+ return std::vector<uint32_t>(Size, VER_NDX_GLOBAL);
+
+ const char *Base = this->MB.getBuffer().data();
+ const Elf_Versym *Versym =
+ reinterpret_cast<const Elf_Versym *>(Base + VersymSec->sh_offset) +
+ this->FirstNonLocal;
+
+ std::vector<uint32_t> Ret(Size);
+ for (size_t I = 0; I < Size; ++I)
+ Ret[I] = Versym[I].vs_index;
+ return Ret;
+}
+
// Parse the version definitions in the object file if present. Returns a vector
// whose nth element contains a pointer to the Elf_Verdef for version identifier
// n. Version identifiers that are not definitions map to nullptr.
template <class ELFT>
-std::vector<const typename ELFT::Verdef *>
-SharedFile<ELFT>::parseVerdefs(const Elf_Versym *&Versym) {
- // We only need to process symbol versions for this DSO if it has both a
- // versym and a verdef section, which indicates that the DSO contains symbol
- // version definitions.
- if (!VersymSec || !VerdefSec)
+std::vector<const typename ELFT::Verdef *> SharedFile<ELFT>::parseVerdefs() {
+ if (!VerdefSec)
return {};
- // The location of the first global versym entry.
- const char *Base = this->MB.getBuffer().data();
- Versym = reinterpret_cast<const Elf_Versym *>(Base + VersymSec->sh_offset) +
- this->FirstNonLocal;
-
// We cannot determine the largest verdef identifier without inspecting
// every Elf_Verdef, but both bfd and gold assign verdef identifiers
// sequentially starting from 1, so we predict that the largest identifier
@@ -808,6 +817,7 @@ SharedFile<ELFT>::parseVerdefs(const Elf
// Build the Verdefs array by following the chain of Elf_Verdef objects
// from the start of the .gnu.version_d section.
+ const char *Base = this->MB.getBuffer().data();
const char *Verdef = Base + VerdefSec->sh_offset;
for (unsigned I = 0; I != VerdefCount; ++I) {
auto *CurVerdef = reinterpret_cast<const Elf_Verdef *>(Verdef);
@@ -821,24 +831,49 @@ SharedFile<ELFT>::parseVerdefs(const Elf
return Verdefs;
}
+// We do not usually care about alignments of data in shared object
+// files because the loader takes care of it. However, if we promote a
+// DSO symbol to point to .bss due to copy relocation, we need to keep
+// the original alignment requirements. We infer it in this function.
+template <class ELFT>
+uint32_t SharedFile<ELFT>::getAlignment(ArrayRef<Elf_Shdr> Sections,
+ const Elf_Sym &Sym) {
+ uint64_t Ret = 1;
+ if (Sym.st_value)
+ Ret = 1ULL << countTrailingZeros((uint64_t)Sym.st_value);
+ if (0 < Sym.st_shndx && Sym.st_shndx < Sections.size())
+ Ret = std::min<uint64_t>(Ret, Sections[Sym.st_shndx].sh_addralign);
+
+ if (Ret > UINT32_MAX)
+ error(toString(this) + ": alignment too large: " +
+ CHECK(Sym.getName(this->StringTable), this));
+ return Ret;
+}
+
// Fully parse the shared object file. This must be called after parseSoName().
+//
+// This function parses symbol versions. If a DSO has version information,
+// the file has a ".gnu.version_d" section which contains symbol version
+// definitions. Each symbol is associated to one version through a table in
+// ".gnu.version" section. That table is a parallel array for the symbol
+// table, and each table entry contains an index in ".gnu.version_d".
+//
+// The special index 0 is reserved for VERF_NDX_LOCAL and 1 is for
+// VER_NDX_GLOBAL. There's no table entry for these special versions in
+// ".gnu.version_d".
+//
+// The file format for symbol versioning is perhaps a bit more complicated
+// than necessary, but you can easily understand the code if you wrap your
+// head around the data structure described above.
template <class ELFT> void SharedFile<ELFT>::parseRest() {
- // Create mapping from version identifiers to Elf_Verdef entries.
- const Elf_Versym *Versym = nullptr;
- Verdefs = parseVerdefs(Versym);
-
+ Verdefs = parseVerdefs(); // parse .gnu.version_d
+ std::vector<uint32_t> Versyms = parseVersyms(); // parse .gnu.version
ArrayRef<Elf_Shdr> Sections = CHECK(this->getObj().sections(), this);
// Add symbols to the symbol table.
- Elf_Sym_Range Syms = this->getGlobalELFSyms();
- for (const Elf_Sym &Sym : Syms) {
- unsigned VersymIndex = VER_NDX_GLOBAL;
- if (Versym) {
- VersymIndex = Versym->vs_index;
- ++Versym;
- }
- bool Hidden = VersymIndex & VERSYM_HIDDEN;
- VersymIndex = VersymIndex & ~VERSYM_HIDDEN;
+ ArrayRef<Elf_Sym> Syms = this->getGlobalELFSyms();
+ for (size_t I = 0; I < Syms.size(); ++I) {
+ const Elf_Sym &Sym = Syms[I];
StringRef Name = CHECK(Sym.getName(this->StringTable), this);
if (Sym.isUndefined()) {
@@ -862,45 +897,31 @@ template <class ELFT> void SharedFile<EL
// MIPS BFD linker puts _gp_disp symbol into DSO files and incorrectly
// assigns VER_NDX_LOCAL to this section global symbol. Here is a
// workaround for this bug.
- if (Config->EMachine == EM_MIPS && VersymIndex == VER_NDX_LOCAL &&
+ uint32_t Idx = Versyms[I] & ~VERSYM_HIDDEN;
+ if (Config->EMachine == EM_MIPS && Idx == VER_NDX_LOCAL &&
Name == "_gp_disp")
continue;
- const Elf_Verdef *Ver = nullptr;
- if (VersymIndex != VER_NDX_GLOBAL) {
- if (VersymIndex >= Verdefs.size() || VersymIndex == VER_NDX_LOCAL) {
- error("corrupt input file: version definition index " +
- Twine(VersymIndex) + " for symbol " + Name +
- " is out of bounds\n>>> defined in " + toString(this));
- continue;
- }
- Ver = Verdefs[VersymIndex];
- }
-
- // We do not usually care about alignments of data in shared object
- // files because the loader takes care of it. However, if we promote a
- // DSO symbol to point to .bss due to copy relocation, we need to keep
- // the original alignment requirements. We infer it here.
- uint64_t Alignment = 1;
- if (Sym.st_value)
- Alignment = 1ULL << countTrailingZeros((uint64_t)Sym.st_value);
- if (0 < Sym.st_shndx && Sym.st_shndx < Sections.size()) {
- uint64_t SecAlign = Sections[Sym.st_shndx].sh_addralign;
- Alignment = std::min(Alignment, SecAlign);
- }
- if (Alignment > UINT32_MAX)
- error(toString(this) + ": alignment too large: " + Name);
-
- if (!Hidden)
- Symtab->addShared(Name, *this, Sym, Alignment, VersymIndex);
+ uint64_t Alignment = getAlignment(Sections, Sym);
+ if (!(Versyms[I] & VERSYM_HIDDEN))
+ Symtab->addShared(Name, *this, Sym, Alignment, Idx);
// Also add the symbol with the versioned name to handle undefined symbols
// with explicit versions.
- if (Ver) {
- StringRef VerName = this->StringTable.data() + Ver->getAux()->vda_name;
- Name = Saver.save(Name + "@" + VerName);
- Symtab->addShared(Name, *this, Sym, Alignment, VersymIndex);
+ if (Idx == VER_NDX_GLOBAL)
+ continue;
+
+ if (Idx >= Verdefs.size() || Idx == VER_NDX_LOCAL) {
+ error("corrupt input file: version definition index " + Twine(Idx) +
+ " for symbol " + Name + " is out of bounds\n>>> defined in " +
+ toString(this));
+ continue;
}
+
+ StringRef VerName =
+ this->StringTable.data() + Verdefs[Idx]->getAux()->vda_name;
+ Name = Saver.save(Name + "@" + VerName);
+ Symtab->addShared(Name, *this, Sym, Alignment, Idx);
}
}
Modified: lld/trunk/ELF/InputFiles.h
URL: http://llvm.org/viewvc/llvm-project/lld/trunk/ELF/InputFiles.h?rev=328579&r1=328578&r2=328579&view=diff
==============================================================================
--- lld/trunk/ELF/InputFiles.h (original)
+++ lld/trunk/ELF/InputFiles.h Mon Mar 26 12:57:38 2018
@@ -308,7 +308,9 @@ public:
void parseSoName();
void parseRest();
- std::vector<const Elf_Verdef *> parseVerdefs(const Elf_Versym *&Versym);
+ uint32_t getAlignment(ArrayRef<Elf_Shdr> Sections, const Elf_Sym &Sym);
+ std::vector<const Elf_Verdef *> parseVerdefs();
+ std::vector<uint32_t> parseVersyms();
struct NeededVer {
// The string table offset of the version name in the output file.
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