[LLD][COFF] Support anti-dependency symbols #112542
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Co-authored-by: Billy Laws <blaws05@gmail.com> Anti-dependency symbols are allowed to be duplicated, with the first definition taking precedence. If a regular weak alias is present, it is preferred over an anti-dependency definition. Chaining anti-dependencies is not allowed.
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@llvm/pr-subscribers-platform-windows @llvm/pr-subscribers-lld-coff Author: Jacek Caban (cjacek) ChangesCo-authored-by: Billy Laws Anti-dependency symbols are allowed to be duplicated, with the first definition taking precedence. If a regular weak alias is present, it is preferred over an anti-dependency definition. Chaining anti-dependencies is not allowed. Full diff: https://github.com/llvm/llvm-project/pull/112542.diff 7 Files Affected:
diff --git a/lld/COFF/Driver.cpp b/lld/COFF/Driver.cpp
index 12e1ae62811270..e7f768789271fa 100644
--- a/lld/COFF/Driver.cpp
+++ b/lld/COFF/Driver.cpp
@@ -737,7 +737,7 @@ StringRef LinkerDriver::mangleMaybe(Symbol *s) {
// If we find a similar mangled symbol, make this an alias to it and return
// its name.
log(unmangled->getName() + " aliased to " + mangled->getName());
- unmangled->weakAlias = ctx.symtab.addUndefined(mangled->getName());
+ unmangled->setWeakAlias(ctx.symtab.addUndefined(mangled->getName()));
return mangled->getName();
}
@@ -2520,7 +2520,7 @@ void LinkerDriver::linkerMain(ArrayRef<const char *> argsArr) {
continue;
if (auto *u = dyn_cast<Undefined>(sym))
if (!u->weakAlias)
- u->weakAlias = ctx.symtab.addUndefined(to);
+ u->setWeakAlias(ctx.symtab.addUndefined(to));
}
// If any inputs are bitcode files, the LTO code generator may create
diff --git a/lld/COFF/InputFiles.cpp b/lld/COFF/InputFiles.cpp
index b19275abebc3ac..292c3bfc1eaa9d 100644
--- a/lld/COFF/InputFiles.cpp
+++ b/lld/COFF/InputFiles.cpp
@@ -74,19 +74,25 @@ std::string lld::toString(const coff::InputFile *file) {
/// If Source is Undefined and has no weak alias set, makes it a weak
/// alias to Target.
static void checkAndSetWeakAlias(COFFLinkerContext &ctx, InputFile *f,
- Symbol *source, Symbol *target) {
+ Symbol *source, Symbol *target,
+ bool isAntiDep) {
if (auto *u = dyn_cast<Undefined>(source)) {
if (u->weakAlias && u->weakAlias != target) {
- // Weak aliases as produced by GCC are named in the form
- // .weak.<weaksymbol>.<othersymbol>, where <othersymbol> is the name
- // of another symbol emitted near the weak symbol.
- // Just use the definition from the first object file that defined
- // this weak symbol.
- if (ctx.config.allowDuplicateWeak)
+ // Ignore duplicated anti-dependency symbols.
+ if (isAntiDep)
return;
- ctx.symtab.reportDuplicate(source, f);
+ if (!u->isAntiDep) {
+ // Weak aliases as produced by GCC are named in the form
+ // .weak.<weaksymbol>.<othersymbol>, where <othersymbol> is the name
+ // of another symbol emitted near the weak symbol.
+ // Just use the definition from the first object file that defined
+ // this weak symbol.
+ if (ctx.config.allowDuplicateWeak)
+ return;
+ ctx.symtab.reportDuplicate(source, f);
+ }
}
- u->weakAlias = target;
+ u->setWeakAlias(target, isAntiDep);
}
}
@@ -436,7 +442,8 @@ void ObjFile::initializeSymbols() {
uint32_t numSymbols = coffObj->getNumberOfSymbols();
symbols.resize(numSymbols);
- SmallVector<std::pair<Symbol *, uint32_t>, 8> weakAliases;
+ SmallVector<std::pair<Symbol *, const coff_aux_weak_external *>, 8>
+ weakAliases;
std::vector<uint32_t> pendingIndexes;
pendingIndexes.reserve(numSymbols);
@@ -451,8 +458,8 @@ void ObjFile::initializeSymbols() {
symbols[i] = createUndefined(coffSym);
} else if (coffSym.isWeakExternal()) {
symbols[i] = createUndefined(coffSym);
- uint32_t tagIndex = coffSym.getAux<coff_aux_weak_external>()->TagIndex;
- weakAliases.emplace_back(symbols[i], tagIndex);
+ weakAliases.emplace_back(symbols[i],
+ coffSym.getAux<coff_aux_weak_external>());
} else if (std::optional<Symbol *> optSym =
createDefined(coffSym, comdatDefs, prevailingComdat)) {
symbols[i] = *optSym;
@@ -491,8 +498,10 @@ void ObjFile::initializeSymbols() {
for (auto &kv : weakAliases) {
Symbol *sym = kv.first;
- uint32_t idx = kv.second;
- checkAndSetWeakAlias(ctx, this, sym, symbols[idx]);
+ const coff_aux_weak_external *aux = kv.second;
+ checkAndSetWeakAlias(ctx, this, sym, symbols[aux->TagIndex],
+ aux->Characteristics ==
+ IMAGE_WEAK_EXTERN_ANTI_DEPENDENCY);
}
// Free the memory used by sparseChunks now that symbol loading is finished.
@@ -1202,7 +1211,7 @@ void BitcodeFile::parse() {
sym = ctx.symtab.addUndefined(symName, this, true);
std::string fallback = std::string(objSym.getCOFFWeakExternalFallback());
Symbol *alias = ctx.symtab.addUndefined(saver.save(fallback));
- checkAndSetWeakAlias(ctx, this, sym, alias);
+ checkAndSetWeakAlias(ctx, this, sym, alias, false);
} else if (comdatIndex != -1) {
if (symName == obj->getComdatTable()[comdatIndex].first) {
sym = comdat[comdatIndex].first;
diff --git a/lld/COFF/SymbolTable.cpp b/lld/COFF/SymbolTable.cpp
index fa09ea64babb28..230ae74dfb21d0 100644
--- a/lld/COFF/SymbolTable.cpp
+++ b/lld/COFF/SymbolTable.cpp
@@ -315,7 +315,7 @@ void SymbolTable::loadMinGWSymbols() {
warn("Resolving " + origName + " by linking to " + newName);
else
log("Resolving " + origName + " by linking to " + newName);
- undef->weakAlias = l;
+ undef->setWeakAlias(l);
continue;
}
}
diff --git a/lld/COFF/Symbols.cpp b/lld/COFF/Symbols.cpp
index 89f2da02bdcf42..f2fa2392ecbbcd 100644
--- a/lld/COFF/Symbols.cpp
+++ b/lld/COFF/Symbols.cpp
@@ -116,6 +116,9 @@ Symbol *Undefined::getWeakAlias() {
// A weak alias may be a weak alias to another symbol, so check recursively.
DenseSet<Symbol *> weakChain;
for (Symbol *a = weakAlias; a; a = cast<Undefined>(a)->weakAlias) {
+ // Anti-dependency symbols can't be chained.
+ if (a->isAntiDep)
+ break;
if (!isa<Undefined>(a))
return a;
if (!weakChain.insert(a).second)
@@ -135,6 +138,7 @@ bool Undefined::resolveWeakAlias() {
// Symbols. For that reason we need to check which type of symbol we
// are dealing with and copy the correct number of bytes.
StringRef name = getName();
+ bool wasAntiDep = isAntiDep;
if (isa<DefinedRegular>(d))
memcpy(this, d, sizeof(DefinedRegular));
else if (isa<DefinedAbsolute>(d))
@@ -144,6 +148,7 @@ bool Undefined::resolveWeakAlias() {
nameData = name.data();
nameSize = name.size();
+ isAntiDep = wasAntiDep;
return true;
}
diff --git a/lld/COFF/Symbols.h b/lld/COFF/Symbols.h
index a898ebf05fd809..ff84ff8ad7b28b 100644
--- a/lld/COFF/Symbols.h
+++ b/lld/COFF/Symbols.h
@@ -100,7 +100,7 @@ class Symbol {
: symbolKind(k), isExternal(true), isCOMDAT(false),
writtenToSymtab(false), isUsedInRegularObj(false),
pendingArchiveLoad(false), isGCRoot(false), isRuntimePseudoReloc(false),
- deferUndefined(false), canInline(true), isWeak(false),
+ deferUndefined(false), canInline(true), isWeak(false), isAntiDep(false),
nameSize(n.size()), nameData(n.empty() ? nullptr : n.data()) {
assert((!n.empty() || k <= LastDefinedCOFFKind) &&
"If the name is empty, the Symbol must be a DefinedCOFF.");
@@ -145,6 +145,9 @@ class Symbol {
// managing weak symbol overrides.
unsigned isWeak : 1;
+ // True if the symbol is an anti-dependency.
+ unsigned isAntiDep : 1;
+
protected:
// Symbol name length. Assume symbol lengths fit in a 32-bit integer.
uint32_t nameSize;
@@ -345,6 +348,11 @@ class Undefined : public Symbol {
return dyn_cast_or_null<Defined>(getWeakAlias());
}
+ void setWeakAlias(Symbol *sym, bool antiDep = false) {
+ weakAlias = sym;
+ isAntiDep = antiDep;
+ }
+
// If this symbol is external weak, replace this object with aliased symbol.
bool resolveWeakAlias();
};
diff --git a/lld/test/COFF/weak-antidep-chain.test b/lld/test/COFF/weak-antidep-chain.test
new file mode 100644
index 00000000000000..f6e32c5139a41e
--- /dev/null
+++ b/lld/test/COFF/weak-antidep-chain.test
@@ -0,0 +1,68 @@
+REQUIRES: x86
+RUN: split-file %s %t.dir && cd %t.dir
+
+RUN: llvm-mc -filetype=obj -triple=x86_64-windows chain-bad.s -o chain-bad.obj
+RUN: llvm-mc -filetype=obj -triple=x86_64-windows chain-bad2.s -o chain-bad2.obj
+RUN: llvm-mc -filetype=obj -triple=x86_64-windows globals-bad.s -o globals-bad.obj
+RUN: llvm-mc -filetype=obj -triple=x86_64-windows chain-good.s -o chain-good.obj
+RUN: llvm-mc -filetype=obj -triple=x86_64-windows chain-good2.s -o chain-good2.obj
+RUN: llvm-mc -filetype=obj -triple=x86_64-windows globals-good.s -o globals-good.obj
+
+Temporary anti-dependency chains are allowed as long as they are broken by non-alias symbols.
+
+RUN: lld-link -machine:amd64 -dll -noentry -out:test.dll chain-good.obj globals-good.obj
+RUN: lld-link -machine:amd64 -dll -noentry -out:test.dll chain-good2.obj globals-good.obj
+
+Chaining of anti-dependency symbols is not allowed.
+
+RUN: not lld-link -machine:amd64 -dll -noentry -out:test.dll chain-bad.obj globals-bad.obj 2>&1 \
+RUN: | FileCheck -check-prefix=ANTIDEP %s
+RUN: not lld-link -machine:amd64 -dll -noentry -out:test.dll chain-bad2.obj globals-bad.obj 2>&1 \
+RUN: | FileCheck -check-prefix=ANTIDEP %s
+
+ANTIDEP: lld-link: error: undefined symbol: sym
+ANTIDEP-NEXT: >>> referenced by chain-bad
+
+#--- chain-bad.s
+ .weak_anti_dep sym
+.set sym,sym2
+ .weak_anti_dep sym2
+.set sym2,sym3
+
+#--- chain-bad2.s
+ .weak_anti_dep sym2
+.set sym2,sym3
+ .weak sym
+.set sym,sym2
+
+#--- globals-bad.s
+ .section .test,"r"
+ .global sym3
+.set sym3,3
+
+#--- chain-good.s
+ .weak_anti_dep sym
+.set sym,sym2
+ .weak_anti_dep sym2
+.set sym2,sym3
+ .weak_anti_dep sym3
+.set sym3,sym4
+ .weak_anti_dep sym4
+
+#--- chain-good2.s
+ .weak_anti_dep sym
+.set sym,sym2
+ .weak_anti_dep sym2
+.set sym2,sym3
+ .weak_anti_dep sym3
+.set sym3,weak_sym
+ .weak weak_sym
+.set weak_sym,sym4
+ .weak_anti_dep sym4
+
+#--- globals-good.s
+ .section .test,"r"
+ .global sym2
+.set sym2,2
+ .global sym4
+.set sym4,4
diff --git a/lld/test/COFF/weak-antidep.test b/lld/test/COFF/weak-antidep.test
new file mode 100644
index 00000000000000..691aa8f184337b
--- /dev/null
+++ b/lld/test/COFF/weak-antidep.test
@@ -0,0 +1,54 @@
+REQUIRES: x86
+RUN: split-file %s %t.dir && cd %t.dir
+
+RUN: llvm-mc -filetype=obj -triple=x86_64-windows antidep.s -o antidep.obj
+RUN: llvm-mc -filetype=obj -triple=x86_64-windows antidep2.s -o antidep2.obj
+RUN: llvm-mc -filetype=obj -triple=x86_64-windows weak.s -o weak.obj
+RUN: llvm-mc -filetype=obj -triple=x86_64-windows test.s -o test.obj
+
+Check that a regular weak alias overrides an anti-dependency symbol.
+
+RUN: lld-link -dll -noentry -out:out1.dll antidep.obj weak.obj test.obj
+RUN: llvm-readobj --hex-dump=.test out1.dll | FileCheck --check-prefix=CHECK2 %s
+
+RUN: lld-link -dll -noentry -out:out2.dll weak.obj antidep.obj test.obj
+RUN: llvm-readobj --hex-dump=.test out2.dll | FileCheck --check-prefix=CHECK2 %s
+
+RUN: lld-link -dll -noentry -out:out3.dll antidep.obj weak.obj test.obj -lld-allow-duplicate-weak
+RUN: llvm-readobj --hex-dump=.test out3.dll | FileCheck --check-prefix=CHECK2 %s
+
+RUN: lld-link -dll -noentry -out:out4.dll weak.obj antidep.obj test.obj -lld-allow-duplicate-weak
+RUN: llvm-readobj --hex-dump=.test out4.dll | FileCheck --check-prefix=CHECK2 %s
+
+When an anti-dependency symbol is duplicated, the first definition takes precedence over subsequent ones.
+
+RUN: lld-link -dll -noentry -out:out5.dll antidep.obj antidep2.obj test.obj
+RUN: llvm-readobj --hex-dump=.test out5.dll | FileCheck --check-prefix=CHECK1 %s
+
+RUN: lld-link -dll -noentry -out:out6.dll antidep2.obj antidep.obj test.obj
+RUN: llvm-readobj --hex-dump=.test out6.dll | FileCheck --check-prefix=CHECK2 %s
+
+CHECK1: 01000000
+CHECK2: 02000000
+
+#--- antidep.s
+ .weak_anti_dep sym
+.set sym,target1
+
+#--- antidep2.s
+ .weak_anti_dep sym
+.set sym,target2
+
+#--- weak.s
+ .weak sym
+.set sym,target2
+
+#--- test.s
+ .section .target,"dr"
+ .globl target1
+.set target1,1
+ .globl target2
+.set target2,2
+
+ .section .test,"dr"
+ .long sym
|
|
@llvm/pr-subscribers-lld Author: Jacek Caban (cjacek) ChangesCo-authored-by: Billy Laws Anti-dependency symbols are allowed to be duplicated, with the first definition taking precedence. If a regular weak alias is present, it is preferred over an anti-dependency definition. Chaining anti-dependencies is not allowed. Full diff: https://github.com/llvm/llvm-project/pull/112542.diff 7 Files Affected:
diff --git a/lld/COFF/Driver.cpp b/lld/COFF/Driver.cpp
index 12e1ae62811270..e7f768789271fa 100644
--- a/lld/COFF/Driver.cpp
+++ b/lld/COFF/Driver.cpp
@@ -737,7 +737,7 @@ StringRef LinkerDriver::mangleMaybe(Symbol *s) {
// If we find a similar mangled symbol, make this an alias to it and return
// its name.
log(unmangled->getName() + " aliased to " + mangled->getName());
- unmangled->weakAlias = ctx.symtab.addUndefined(mangled->getName());
+ unmangled->setWeakAlias(ctx.symtab.addUndefined(mangled->getName()));
return mangled->getName();
}
@@ -2520,7 +2520,7 @@ void LinkerDriver::linkerMain(ArrayRef<const char *> argsArr) {
continue;
if (auto *u = dyn_cast<Undefined>(sym))
if (!u->weakAlias)
- u->weakAlias = ctx.symtab.addUndefined(to);
+ u->setWeakAlias(ctx.symtab.addUndefined(to));
}
// If any inputs are bitcode files, the LTO code generator may create
diff --git a/lld/COFF/InputFiles.cpp b/lld/COFF/InputFiles.cpp
index b19275abebc3ac..292c3bfc1eaa9d 100644
--- a/lld/COFF/InputFiles.cpp
+++ b/lld/COFF/InputFiles.cpp
@@ -74,19 +74,25 @@ std::string lld::toString(const coff::InputFile *file) {
/// If Source is Undefined and has no weak alias set, makes it a weak
/// alias to Target.
static void checkAndSetWeakAlias(COFFLinkerContext &ctx, InputFile *f,
- Symbol *source, Symbol *target) {
+ Symbol *source, Symbol *target,
+ bool isAntiDep) {
if (auto *u = dyn_cast<Undefined>(source)) {
if (u->weakAlias && u->weakAlias != target) {
- // Weak aliases as produced by GCC are named in the form
- // .weak.<weaksymbol>.<othersymbol>, where <othersymbol> is the name
- // of another symbol emitted near the weak symbol.
- // Just use the definition from the first object file that defined
- // this weak symbol.
- if (ctx.config.allowDuplicateWeak)
+ // Ignore duplicated anti-dependency symbols.
+ if (isAntiDep)
return;
- ctx.symtab.reportDuplicate(source, f);
+ if (!u->isAntiDep) {
+ // Weak aliases as produced by GCC are named in the form
+ // .weak.<weaksymbol>.<othersymbol>, where <othersymbol> is the name
+ // of another symbol emitted near the weak symbol.
+ // Just use the definition from the first object file that defined
+ // this weak symbol.
+ if (ctx.config.allowDuplicateWeak)
+ return;
+ ctx.symtab.reportDuplicate(source, f);
+ }
}
- u->weakAlias = target;
+ u->setWeakAlias(target, isAntiDep);
}
}
@@ -436,7 +442,8 @@ void ObjFile::initializeSymbols() {
uint32_t numSymbols = coffObj->getNumberOfSymbols();
symbols.resize(numSymbols);
- SmallVector<std::pair<Symbol *, uint32_t>, 8> weakAliases;
+ SmallVector<std::pair<Symbol *, const coff_aux_weak_external *>, 8>
+ weakAliases;
std::vector<uint32_t> pendingIndexes;
pendingIndexes.reserve(numSymbols);
@@ -451,8 +458,8 @@ void ObjFile::initializeSymbols() {
symbols[i] = createUndefined(coffSym);
} else if (coffSym.isWeakExternal()) {
symbols[i] = createUndefined(coffSym);
- uint32_t tagIndex = coffSym.getAux<coff_aux_weak_external>()->TagIndex;
- weakAliases.emplace_back(symbols[i], tagIndex);
+ weakAliases.emplace_back(symbols[i],
+ coffSym.getAux<coff_aux_weak_external>());
} else if (std::optional<Symbol *> optSym =
createDefined(coffSym, comdatDefs, prevailingComdat)) {
symbols[i] = *optSym;
@@ -491,8 +498,10 @@ void ObjFile::initializeSymbols() {
for (auto &kv : weakAliases) {
Symbol *sym = kv.first;
- uint32_t idx = kv.second;
- checkAndSetWeakAlias(ctx, this, sym, symbols[idx]);
+ const coff_aux_weak_external *aux = kv.second;
+ checkAndSetWeakAlias(ctx, this, sym, symbols[aux->TagIndex],
+ aux->Characteristics ==
+ IMAGE_WEAK_EXTERN_ANTI_DEPENDENCY);
}
// Free the memory used by sparseChunks now that symbol loading is finished.
@@ -1202,7 +1211,7 @@ void BitcodeFile::parse() {
sym = ctx.symtab.addUndefined(symName, this, true);
std::string fallback = std::string(objSym.getCOFFWeakExternalFallback());
Symbol *alias = ctx.symtab.addUndefined(saver.save(fallback));
- checkAndSetWeakAlias(ctx, this, sym, alias);
+ checkAndSetWeakAlias(ctx, this, sym, alias, false);
} else if (comdatIndex != -1) {
if (symName == obj->getComdatTable()[comdatIndex].first) {
sym = comdat[comdatIndex].first;
diff --git a/lld/COFF/SymbolTable.cpp b/lld/COFF/SymbolTable.cpp
index fa09ea64babb28..230ae74dfb21d0 100644
--- a/lld/COFF/SymbolTable.cpp
+++ b/lld/COFF/SymbolTable.cpp
@@ -315,7 +315,7 @@ void SymbolTable::loadMinGWSymbols() {
warn("Resolving " + origName + " by linking to " + newName);
else
log("Resolving " + origName + " by linking to " + newName);
- undef->weakAlias = l;
+ undef->setWeakAlias(l);
continue;
}
}
diff --git a/lld/COFF/Symbols.cpp b/lld/COFF/Symbols.cpp
index 89f2da02bdcf42..f2fa2392ecbbcd 100644
--- a/lld/COFF/Symbols.cpp
+++ b/lld/COFF/Symbols.cpp
@@ -116,6 +116,9 @@ Symbol *Undefined::getWeakAlias() {
// A weak alias may be a weak alias to another symbol, so check recursively.
DenseSet<Symbol *> weakChain;
for (Symbol *a = weakAlias; a; a = cast<Undefined>(a)->weakAlias) {
+ // Anti-dependency symbols can't be chained.
+ if (a->isAntiDep)
+ break;
if (!isa<Undefined>(a))
return a;
if (!weakChain.insert(a).second)
@@ -135,6 +138,7 @@ bool Undefined::resolveWeakAlias() {
// Symbols. For that reason we need to check which type of symbol we
// are dealing with and copy the correct number of bytes.
StringRef name = getName();
+ bool wasAntiDep = isAntiDep;
if (isa<DefinedRegular>(d))
memcpy(this, d, sizeof(DefinedRegular));
else if (isa<DefinedAbsolute>(d))
@@ -144,6 +148,7 @@ bool Undefined::resolveWeakAlias() {
nameData = name.data();
nameSize = name.size();
+ isAntiDep = wasAntiDep;
return true;
}
diff --git a/lld/COFF/Symbols.h b/lld/COFF/Symbols.h
index a898ebf05fd809..ff84ff8ad7b28b 100644
--- a/lld/COFF/Symbols.h
+++ b/lld/COFF/Symbols.h
@@ -100,7 +100,7 @@ class Symbol {
: symbolKind(k), isExternal(true), isCOMDAT(false),
writtenToSymtab(false), isUsedInRegularObj(false),
pendingArchiveLoad(false), isGCRoot(false), isRuntimePseudoReloc(false),
- deferUndefined(false), canInline(true), isWeak(false),
+ deferUndefined(false), canInline(true), isWeak(false), isAntiDep(false),
nameSize(n.size()), nameData(n.empty() ? nullptr : n.data()) {
assert((!n.empty() || k <= LastDefinedCOFFKind) &&
"If the name is empty, the Symbol must be a DefinedCOFF.");
@@ -145,6 +145,9 @@ class Symbol {
// managing weak symbol overrides.
unsigned isWeak : 1;
+ // True if the symbol is an anti-dependency.
+ unsigned isAntiDep : 1;
+
protected:
// Symbol name length. Assume symbol lengths fit in a 32-bit integer.
uint32_t nameSize;
@@ -345,6 +348,11 @@ class Undefined : public Symbol {
return dyn_cast_or_null<Defined>(getWeakAlias());
}
+ void setWeakAlias(Symbol *sym, bool antiDep = false) {
+ weakAlias = sym;
+ isAntiDep = antiDep;
+ }
+
// If this symbol is external weak, replace this object with aliased symbol.
bool resolveWeakAlias();
};
diff --git a/lld/test/COFF/weak-antidep-chain.test b/lld/test/COFF/weak-antidep-chain.test
new file mode 100644
index 00000000000000..f6e32c5139a41e
--- /dev/null
+++ b/lld/test/COFF/weak-antidep-chain.test
@@ -0,0 +1,68 @@
+REQUIRES: x86
+RUN: split-file %s %t.dir && cd %t.dir
+
+RUN: llvm-mc -filetype=obj -triple=x86_64-windows chain-bad.s -o chain-bad.obj
+RUN: llvm-mc -filetype=obj -triple=x86_64-windows chain-bad2.s -o chain-bad2.obj
+RUN: llvm-mc -filetype=obj -triple=x86_64-windows globals-bad.s -o globals-bad.obj
+RUN: llvm-mc -filetype=obj -triple=x86_64-windows chain-good.s -o chain-good.obj
+RUN: llvm-mc -filetype=obj -triple=x86_64-windows chain-good2.s -o chain-good2.obj
+RUN: llvm-mc -filetype=obj -triple=x86_64-windows globals-good.s -o globals-good.obj
+
+Temporary anti-dependency chains are allowed as long as they are broken by non-alias symbols.
+
+RUN: lld-link -machine:amd64 -dll -noentry -out:test.dll chain-good.obj globals-good.obj
+RUN: lld-link -machine:amd64 -dll -noentry -out:test.dll chain-good2.obj globals-good.obj
+
+Chaining of anti-dependency symbols is not allowed.
+
+RUN: not lld-link -machine:amd64 -dll -noentry -out:test.dll chain-bad.obj globals-bad.obj 2>&1 \
+RUN: | FileCheck -check-prefix=ANTIDEP %s
+RUN: not lld-link -machine:amd64 -dll -noentry -out:test.dll chain-bad2.obj globals-bad.obj 2>&1 \
+RUN: | FileCheck -check-prefix=ANTIDEP %s
+
+ANTIDEP: lld-link: error: undefined symbol: sym
+ANTIDEP-NEXT: >>> referenced by chain-bad
+
+#--- chain-bad.s
+ .weak_anti_dep sym
+.set sym,sym2
+ .weak_anti_dep sym2
+.set sym2,sym3
+
+#--- chain-bad2.s
+ .weak_anti_dep sym2
+.set sym2,sym3
+ .weak sym
+.set sym,sym2
+
+#--- globals-bad.s
+ .section .test,"r"
+ .global sym3
+.set sym3,3
+
+#--- chain-good.s
+ .weak_anti_dep sym
+.set sym,sym2
+ .weak_anti_dep sym2
+.set sym2,sym3
+ .weak_anti_dep sym3
+.set sym3,sym4
+ .weak_anti_dep sym4
+
+#--- chain-good2.s
+ .weak_anti_dep sym
+.set sym,sym2
+ .weak_anti_dep sym2
+.set sym2,sym3
+ .weak_anti_dep sym3
+.set sym3,weak_sym
+ .weak weak_sym
+.set weak_sym,sym4
+ .weak_anti_dep sym4
+
+#--- globals-good.s
+ .section .test,"r"
+ .global sym2
+.set sym2,2
+ .global sym4
+.set sym4,4
diff --git a/lld/test/COFF/weak-antidep.test b/lld/test/COFF/weak-antidep.test
new file mode 100644
index 00000000000000..691aa8f184337b
--- /dev/null
+++ b/lld/test/COFF/weak-antidep.test
@@ -0,0 +1,54 @@
+REQUIRES: x86
+RUN: split-file %s %t.dir && cd %t.dir
+
+RUN: llvm-mc -filetype=obj -triple=x86_64-windows antidep.s -o antidep.obj
+RUN: llvm-mc -filetype=obj -triple=x86_64-windows antidep2.s -o antidep2.obj
+RUN: llvm-mc -filetype=obj -triple=x86_64-windows weak.s -o weak.obj
+RUN: llvm-mc -filetype=obj -triple=x86_64-windows test.s -o test.obj
+
+Check that a regular weak alias overrides an anti-dependency symbol.
+
+RUN: lld-link -dll -noentry -out:out1.dll antidep.obj weak.obj test.obj
+RUN: llvm-readobj --hex-dump=.test out1.dll | FileCheck --check-prefix=CHECK2 %s
+
+RUN: lld-link -dll -noentry -out:out2.dll weak.obj antidep.obj test.obj
+RUN: llvm-readobj --hex-dump=.test out2.dll | FileCheck --check-prefix=CHECK2 %s
+
+RUN: lld-link -dll -noentry -out:out3.dll antidep.obj weak.obj test.obj -lld-allow-duplicate-weak
+RUN: llvm-readobj --hex-dump=.test out3.dll | FileCheck --check-prefix=CHECK2 %s
+
+RUN: lld-link -dll -noentry -out:out4.dll weak.obj antidep.obj test.obj -lld-allow-duplicate-weak
+RUN: llvm-readobj --hex-dump=.test out4.dll | FileCheck --check-prefix=CHECK2 %s
+
+When an anti-dependency symbol is duplicated, the first definition takes precedence over subsequent ones.
+
+RUN: lld-link -dll -noentry -out:out5.dll antidep.obj antidep2.obj test.obj
+RUN: llvm-readobj --hex-dump=.test out5.dll | FileCheck --check-prefix=CHECK1 %s
+
+RUN: lld-link -dll -noentry -out:out6.dll antidep2.obj antidep.obj test.obj
+RUN: llvm-readobj --hex-dump=.test out6.dll | FileCheck --check-prefix=CHECK2 %s
+
+CHECK1: 01000000
+CHECK2: 02000000
+
+#--- antidep.s
+ .weak_anti_dep sym
+.set sym,target1
+
+#--- antidep2.s
+ .weak_anti_dep sym
+.set sym,target2
+
+#--- weak.s
+ .weak sym
+.set sym,target2
+
+#--- test.s
+ .section .target,"dr"
+ .globl target1
+.set target1,1
+ .globl target2
+.set target2,2
+
+ .section .test,"dr"
+ .long sym
|
|
Anti-dependency symbols are, unfortunately, not documented. This PR implements their behavior as observed in MSVC. Anti-dependency symbols are used extensively in ARM64EC. In situations where typical targets would emit an undefined symbol for an external function, ARM64EC object files don't initially know if the implementation will be ARM64EC (in which case the mangled symbol name can be used directly) or x86_64 (in which case the mangled symbol must resolve to a thunk that calls the demangled symbol via an emulator). The setup involves the demangled If regular weak aliases were used instead, those symbols would always be resolvable: both Since each object file referencing the function emits these anti-dependency aliases, they are frequently duplicated, which is acceptable for anti-dependencies. Usually, functions built as ARM64EC include a Like other weak aliases, an anti-dependency alias prevents the symbol from being resolved via a static library symbol. This means that ARM64EC object files' usage of these aliases would not work for referencing static libraries. According to my testing, MSVC has an ARM64EC-specific feature that detects the mangled I also observed some unexplained behavior in MSVC where the order of definitions seems to matter. For example, the last two weak-antidep.test tests fail in MSVC if CC @bylaws |
mstorsjo
approved these changes
Oct 18, 2024
| @@ -737,7 +737,7 @@ StringRef LinkerDriver::mangleMaybe(Symbol *s) { | |||
| // If we find a similar mangled symbol, make this an alias to it and return | |||
| // its name. | |||
| log(unmangled->getName() + " aliased to " + mangled->getName()); | |||
| unmangled->weakAlias = ctx.symtab.addUndefined(mangled->getName()); | |||
| unmangled->setWeakAlias(ctx.symtab.addUndefined(mangled->getName())); | |||
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As the weakAlias member hasn't been made private here, I presume, and we're passing the default of false to the antiDep parameter, I guess these changes strictly are unnecessary? It's of course nice for consistency to add them, but if working on the codebase going forward, there's no guarantee that new calls will use this form, as they may just as well just assign to weakAlias?
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We could make it private, but it will need a few more changes. As getWeakAlias follows the chain, it's not a replacement for accessing weakAlias directly. I will create a follow-up, thanks!
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I'm not sure if that's really necessary - I was just checking I understood the situation correctly :-)
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Co-authored-by: Billy Laws
Anti-dependency symbols are allowed to be duplicated, with the first definition taking precedence. If a regular weak alias is present, it is preferred over an anti-dependency definition. Chaining anti-dependencies is not allowed.