[lld] [ELF] Merge exportDynamic into versionId (PR #71272)
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Fri Nov 3 21:29:27 PDT 2023
llvmbot wrote:
<!--LLVM PR SUMMARY COMMENT-->
@llvm/pr-subscribers-lld-elf
Author: Fangrui Song (MaskRay)
<details>
<summary>Changes</summary>
For a Defined/Common symbol with a false `inDynamicList`, both
`versionId==VER_NDX_LOCAL` and `!exportDynamic` indicate that the symbol
should not be exported, which means that the two fields have overlapping
purposes. We can merge them together by reserving `versionId==-1` to
indicate a symbol that is not exported:
* -1 (initial): not exported, binding unchanged
* 0: VER_NDX_LOCAL, not exported, binding changed to STB_LOCAL
* 1: VER_NDX_GLOBAL, exported, binding unchanged
* others: verdef index, exported, binding unchanged
-1 and 0 are similar, but -1 does not change the binding to STB_LOCAL.
The saved bit can be use for another purpose, e.g. whether a symbol has
a DSO definition (#<!-- -->70130).
--version-script is almost never used for executables. If used, a minor behavior
change is that a version pattern that is not `local:` will export the matched
symbols.
---
Full diff: https://github.com/llvm/llvm-project/pull/71272.diff
10 Files Affected:
- (modified) lld/ELF/Config.h (+1)
- (modified) lld/ELF/Driver.cpp (+3)
- (modified) lld/ELF/InputFiles.cpp (+2-2)
- (modified) lld/ELF/LTO.cpp (+3-3)
- (modified) lld/ELF/Relocations.cpp (+2-2)
- (modified) lld/ELF/SymbolTable.cpp (+1-1)
- (modified) lld/ELF/Symbols.cpp (+8-8)
- (modified) lld/ELF/Symbols.h (+25-17)
- (modified) lld/ELF/SyntheticSections.cpp (+2-1)
- (modified) lld/test/ELF/version-script-symver.s (+1-3)
``````````diff
diff --git a/lld/ELF/Config.h b/lld/ELF/Config.h
index 56229334f9a44ae..06fef790d1e5439 100644
--- a/lld/ELF/Config.h
+++ b/lld/ELF/Config.h
@@ -225,6 +225,7 @@ struct Config {
bool cref;
llvm::SmallVector<std::pair<llvm::GlobPattern, uint64_t>, 0>
deadRelocInNonAlloc;
+ uint16_t defaultVersionId;
bool demangle = true;
bool dependentLibraries;
bool disableVerify;
diff --git a/lld/ELF/Driver.cpp b/lld/ELF/Driver.cpp
index 6290880c43d3b95..2e1214ae4087364 100644
--- a/lld/ELF/Driver.cpp
+++ b/lld/ELF/Driver.cpp
@@ -1683,6 +1683,9 @@ static void readConfigs(opt::InputArgList &args) {
}
}
+ config->defaultVersionId =
+ config->exportDynamic ? ELF::VER_NDX_GLOBAL : nonExported;
+
assert(config->versionDefinitions.empty());
config->versionDefinitions.push_back(
{"local", (uint16_t)VER_NDX_LOCAL, {}, {}});
diff --git a/lld/ELF/InputFiles.cpp b/lld/ELF/InputFiles.cpp
index a0d4be8ff9885b0..1ac94e179688fee 100644
--- a/lld/ELF/InputFiles.cpp
+++ b/lld/ELF/InputFiles.cpp
@@ -1520,7 +1520,7 @@ template <class ELFT> void SharedFile::parse() {
}
Symbol *s = symtab.addSymbol(
Undefined{this, name, sym.getBinding(), sym.st_other, sym.getType()});
- s->exportDynamic = true;
+ s->versionId = VER_NDX_GLOBAL;
if (s->isUndefined() && sym.getBinding() != STB_WEAK &&
config->unresolvedSymbolsInShlib != UnresolvedPolicy::Ignore)
requiredSymbols.push_back(s);
@@ -1698,7 +1698,7 @@ createBitcodeSymbol(Symbol *&sym, const std::vector<bool> &keptComdats,
} else {
Defined newSym(&f, StringRef(), binding, visibility, type, 0, 0, nullptr);
if (objSym.canBeOmittedFromSymbolTable())
- newSym.exportDynamic = false;
+ newSym.versionId = nonExported;
sym->resolve(newSym);
}
}
diff --git a/lld/ELF/LTO.cpp b/lld/ELF/LTO.cpp
index 504c12aac6c5696..e534f159e5e42be 100644
--- a/lld/ELF/LTO.cpp
+++ b/lld/ELF/LTO.cpp
@@ -245,9 +245,9 @@ void BitcodeCompiler::add(BitcodeFile &f) {
usedStartStop.count(objSym.getSectionName());
// Identify symbols exported dynamically, and that therefore could be
// referenced by a shared library not visible to the linker.
- r.ExportDynamic =
- sym->computeBinding() != STB_LOCAL &&
- (config->exportDynamic || sym->exportDynamic || sym->inDynamicList);
+ r.ExportDynamic = sym->computeBinding() != STB_LOCAL &&
+ (config->exportDynamic || sym->versionId != nonExported ||
+ sym->inDynamicList);
const auto *dr = dyn_cast<Defined>(sym);
r.FinalDefinitionInLinkageUnit =
(isExec || sym->visibility() != STV_DEFAULT) && dr &&
diff --git a/lld/ELF/Relocations.cpp b/lld/ELF/Relocations.cpp
index 6765461805dadb0..cbf6c42cd2d9b8d 100644
--- a/lld/ELF/Relocations.cpp
+++ b/lld/ELF/Relocations.cpp
@@ -310,7 +310,7 @@ static void replaceWithDefined(Symbol &sym, SectionBase &sec, uint64_t value,
.overwrite(sym);
sym.verdefIndex = old.verdefIndex;
- sym.exportDynamic = true;
+ sym.exportIfNonExported();
sym.isUsedInRegularObj = true;
// A copy relocated alias may need a GOT entry.
sym.flags.store(old.flags.load(std::memory_order_relaxed) & NEEDS_GOT,
@@ -1068,7 +1068,7 @@ void RelocationScanner::processAux(RelExpr expr, RelType type, uint64_t offset,
// direct relocation on through.
if (LLVM_UNLIKELY(isIfunc) && config->zIfuncNoplt) {
std::lock_guard<std::mutex> lock(relocMutex);
- sym.exportDynamic = true;
+ sym.exportIfNonExported();
mainPart->relaDyn->addSymbolReloc(type, *sec, offset, sym, addend, type);
return;
}
diff --git a/lld/ELF/SymbolTable.cpp b/lld/ELF/SymbolTable.cpp
index fe7edd5b0eb49aa..1d8459c0db96857 100644
--- a/lld/ELF/SymbolTable.cpp
+++ b/lld/ELF/SymbolTable.cpp
@@ -93,7 +93,7 @@ Symbol *SymbolTable::insert(StringRef name) {
sym->setName(name);
sym->partition = 1;
sym->verdefIndex = -1;
- sym->versionId = VER_NDX_GLOBAL;
+ sym->versionId = nonExported;
if (pos != StringRef::npos)
sym->hasVersionSuffix = true;
return sym;
diff --git a/lld/ELF/Symbols.cpp b/lld/ELF/Symbols.cpp
index 671eb56f3404c95..0972a77fecfc32a 100644
--- a/lld/ELF/Symbols.cpp
+++ b/lld/ELF/Symbols.cpp
@@ -287,7 +287,7 @@ bool Symbol::includeInDynsym() const {
// __pthread_initialize_minimal reference in csu/libc-start.c.
return !(isUndefWeak() && config->noDynamicLinker);
- return exportDynamic || inDynamicList;
+ return versionId != nonExported || inDynamicList;
}
// Print out a log message for --trace-symbol.
@@ -384,8 +384,8 @@ bool elf::computeIsPreemptible(const Symbol &sym) {
// and that's the result of symbol resolution. However, symbols that
// were not chosen still affect some symbol properties.
void Symbol::mergeProperties(const Symbol &other) {
- if (other.exportDynamic)
- exportDynamic = true;
+ if (versionId == nonExported)
+ versionId = other.versionId;
// DSO symbols do not affect visibility in the output.
if (!other.isShared() && other.visibility() != STV_DEFAULT) {
@@ -575,8 +575,8 @@ void Symbol::checkDuplicate(const Defined &other) const {
}
void Symbol::resolve(const CommonSymbol &other) {
- if (other.exportDynamic)
- exportDynamic = true;
+ if (versionId == nonExported)
+ versionId = other.versionId;
if (other.visibility() != STV_DEFAULT) {
uint8_t v = visibility(), ov = other.visibility();
setVisibility(v == STV_DEFAULT ? ov : std::min(v, ov));
@@ -613,8 +613,8 @@ void Symbol::resolve(const CommonSymbol &other) {
}
void Symbol::resolve(const Defined &other) {
- if (other.exportDynamic)
- exportDynamic = true;
+ if (versionId == nonExported)
+ versionId = other.versionId;
if (other.visibility() != STV_DEFAULT) {
uint8_t v = visibility(), ov = other.visibility();
setVisibility(v == STV_DEFAULT ? ov : std::min(v, ov));
@@ -663,7 +663,7 @@ void Symbol::resolve(const LazyObject &other) {
}
void Symbol::resolve(const SharedSymbol &other) {
- exportDynamic = true;
+ exportIfNonExported();
if (isPlaceholder()) {
other.overwrite(*this);
return;
diff --git a/lld/ELF/Symbols.h b/lld/ELF/Symbols.h
index 4addb79d1257914..29eccb29fdd23da 100644
--- a/lld/ELF/Symbols.h
+++ b/lld/ELF/Symbols.h
@@ -67,6 +67,9 @@ struct SymbolAux {
LLVM_LIBRARY_VISIBILITY extern SmallVector<SymbolAux, 0> symAux;
+// A versionId value similar to VER_NDX_LOCAL, but the binding is not changed.
+constexpr uint16_t nonExported = uint16_t(-1);
+
// The base class for real symbol classes.
class Symbol {
public:
@@ -129,17 +132,6 @@ class Symbol {
// which are referenced by relocations when -r or --emit-relocs is given.
uint8_t used : 1;
- // Used by a Defined symbol with protected or default visibility, to record
- // whether it is required to be exported into .dynsym. This is set when any of
- // the following conditions hold:
- //
- // - If there is an interposable symbol from a DSO. Note: We also do this for
- // STV_PROTECTED symbols which can't be interposed (to match BFD behavior).
- // - If -shared or --export-dynamic is specified, any symbol in an object
- // file/bitcode sets this property, unless suppressed by LTO
- // canBeOmittedFromSymbolTable().
- uint8_t exportDynamic : 1;
-
// True if the symbol is in the --dynamic-list file. A Defined symbol with
// protected or default visibility with this property is required to be
// exported into .dynsym.
@@ -254,7 +246,7 @@ class Symbol {
Symbol(Kind k, InputFile *file, StringRef name, uint8_t binding,
uint8_t stOther, uint8_t type)
: file(file), nameData(name.data()), nameSize(name.size()), type(type),
- binding(binding), stOther(stOther), symbolKind(k), exportDynamic(false),
+ binding(binding), stOther(stOther), symbolKind(k),
archSpecificBit(false) {}
void overwrite(Symbol &sym, Kind k) const {
@@ -316,9 +308,25 @@ class Symbol {
// This field is a index to the symbol's version definition.
uint16_t verdefIndex;
- // Version definition index.
- uint16_t versionId;
+ // Used by a Defined symbol with protected or default visibility, to record
+ // the verdef index and whether the symbol is exported into .dynsym.
+ // * -1 (initial): not exported, binding unchanged
+ // * 0: VER_NDX_LOCAL, not exported, binding changed to STB_LOCAL
+ // * 1: VER_NDX_GLOBAL, exported, binding unchanged
+ // * others: verdef index, exported, binding unchanged
+ //
+ // -1 transits to 1 if any of the following conditions hold:
+ // * If there is an interposable symbol from a DSO. Note: We also do this for
+ // STV_PROTECTED symbols which can't be interposed (to match BFD behavior).
+ // * If -shared or --export-dynamic is specified, any symbol in an object
+ // file/bitcode sets this property, unless suppressed by LTO
+ // canBeOmittedFromSymbolTable().
+ uint16_t versionId = nonExported;
+ void exportIfNonExported() {
+ if (versionId == nonExported)
+ versionId = llvm::ELF::VER_NDX_GLOBAL;
+ }
void setFlags(uint16_t bits) {
flags.fetch_or(bits, std::memory_order_relaxed);
}
@@ -353,7 +361,7 @@ class Defined : public Symbol {
uint8_t type, uint64_t value, uint64_t size, SectionBase *section)
: Symbol(DefinedKind, file, name, binding, stOther, type), value(value),
size(size), section(section) {
- exportDynamic = config->exportDynamic;
+ versionId = config->defaultVersionId;
}
void overwrite(Symbol &sym) const {
Symbol::overwrite(sym, DefinedKind);
@@ -398,7 +406,7 @@ class CommonSymbol : public Symbol {
uint8_t stOther, uint8_t type, uint64_t alignment, uint64_t size)
: Symbol(CommonKind, file, name, binding, stOther, type),
alignment(alignment), size(size) {
- exportDynamic = config->exportDynamic;
+ versionId = config->defaultVersionId;
}
void overwrite(Symbol &sym) const {
Symbol::overwrite(sym, CommonKind);
@@ -442,7 +450,7 @@ class SharedSymbol : public Symbol {
uint32_t alignment)
: Symbol(SharedKind, &file, name, binding, stOther, type), value(value),
size(size), alignment(alignment) {
- exportDynamic = true;
+ versionId = llvm::ELF::VER_NDX_GLOBAL;
dsoProtected = visibility() == llvm::ELF::STV_PROTECTED;
// GNU ifunc is a mechanism to allow user-supplied functions to
// resolve PLT slot values at load-time. This is contrary to the
diff --git a/lld/ELF/SyntheticSections.cpp b/lld/ELF/SyntheticSections.cpp
index 0f7ebf9d7ba840b..235c0de07ab81a4 100644
--- a/lld/ELF/SyntheticSections.cpp
+++ b/lld/ELF/SyntheticSections.cpp
@@ -3128,7 +3128,8 @@ void VersionTableSection::writeTo(uint8_t *buf) {
// For an unextracted lazy symbol (undefined weak), it must have been
// converted to Undefined and have VER_NDX_GLOBAL version here.
assert(!s.sym->isLazy());
- write16(buf, s.sym->versionId);
+ write16(buf, s.sym->versionId == uint16_t(-1) ? VER_NDX_GLOBAL
+ : s.sym->versionId);
buf += 2;
}
}
diff --git a/lld/test/ELF/version-script-symver.s b/lld/test/ELF/version-script-symver.s
index db7c6f434ff4e57..798d9dbc5d7f144 100644
--- a/lld/test/ELF/version-script-symver.s
+++ b/lld/test/ELF/version-script-symver.s
@@ -42,9 +42,7 @@
# RUN: ld.lld --version-script %t4.script -pie --export-dynamic %t.o -o %t4
# RUN: llvm-readelf --dyn-syms %t4 | FileCheck --check-prefix=MIX2 %s
# RUN: ld.lld --version-script %t4.script -pie %t.o -o %t4
-# RUN: llvm-readelf --dyn-syms %t4 | FileCheck --check-prefix=EXE %s
-
-# EXE: Symbol table '.dynsym' contains 1 entries:
+# RUN: llvm-readelf --dyn-syms %t4 | FileCheck --check-prefix=MIX2 %s
# RUN: ld.lld --version-script %t4.script -shared %t.o %tref.o -o %t5.so
# RUN: llvm-readelf -r %t5.so | FileCheck --check-prefix=RELOC %s
``````````
</details>
https://github.com/llvm/llvm-project/pull/71272
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