[COFF] Fix /export:foo=bar when bar is a weak alias
Summary:
When handling exports from the command line or from .def files, the
linker does a "fuzzy" string lookup to allow finding mangled symbols.
However, when the symbol is re-exported under a new name, the linker has
to transfer the decorations from the exported symbol over to the new
name. This is implemented by taking the mangled symbol that was found in
the object and replacing the original symbol name with the export name.
Before this patch, LLD implemented the fuzzy search by adding an
undefined symbol with the unmangled name, and then during symbol
resolution, checking if similar mangled symbols had been added after the
last round of symbol resolution. If so, LLD makes the original symbol a
weak alias of the mangled symbol. Later, to get the original symbol
name, LLD would look through the weak alias and forward it on to the
import library writer, which copies the symbol decorations. This
approach doesn't work when bar is itself a weak alias, as is the case in
asan. It's especially bad when the aliasee of bar contains the string
"bar", consider "bar_default". In this case, we would end up exporting
the symbol "foo_default" when we should've exported just "foo".
To fix this, don't look through weak aliases to find the mangled name.
Save the mangled name earlier during fuzzy symbol lookup.
Fixes PR42074
Reviewers: mstorsjo, ruiu
Subscribers: thakis, llvm-commits
Tags: #llvm
Differential Revision: https://reviews.llvm.org/D62984
git-svn-id: https://llvm.org/svn/llvm-project/lld/trunk@362849 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/COFF/Driver.cpp b/COFF/Driver.cpp
index 7f7fde1..ef25fe3 100644
--- a/COFF/Driver.cpp
+++ b/COFF/Driver.cpp
@@ -138,8 +138,8 @@
}
static bool findUnderscoreMangle(StringRef Sym) {
- StringRef Entry = Symtab->findMangle(mangle(Sym));
- return !Entry.empty() && !isa<Undefined>(Symtab->find(Entry));
+ Symbol *S = Symtab->findMangle(mangle(Sym));
+ return S && !isa<Undefined>(S);
}
MemoryBufferRef LinkerDriver::takeBuffer(std::unique_ptr<MemoryBuffer> MB) {
@@ -486,6 +486,24 @@
return B;
}
+StringRef LinkerDriver::mangleMaybe(Symbol *S) {
+ // If the plain symbol name has already been resolved, do nothing.
+ Undefined *Unmangled = dyn_cast<Undefined>(S);
+ if (!Unmangled)
+ return "";
+
+ // Otherwise, see if a similar, mangled symbol exists in the symbol table.
+ Symbol *Mangled = Symtab->findMangle(Unmangled->getName());
+ if (!Mangled)
+ return "";
+
+ // 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 = Symtab->addUndefined(Mangled->getName());
+ return Mangled->getName();
+}
+
// Windows specific -- find default entry point name.
//
// There are four different entry point functions for Windows executables,
@@ -1644,7 +1662,7 @@
// Windows specific -- if entry point is not found,
// search for its mangled names.
if (Config->Entry)
- Symtab->mangleMaybe(Config->Entry);
+ mangleMaybe(Config->Entry);
// Windows specific -- Make sure we resolve all dllexported symbols.
for (Export &E : Config->Exports) {
@@ -1652,7 +1670,7 @@
continue;
E.Sym = addUndefined(E.Name);
if (!E.Directives)
- Symtab->mangleMaybe(E.Sym);
+ E.SymbolName = mangleMaybe(E.Sym);
}
// Add weak aliases. Weak aliases is a mechanism to give remaining
diff --git a/COFF/Driver.h b/COFF/Driver.h
index f0c2ee6..6b4266a 100644
--- a/COFF/Driver.h
+++ b/COFF/Driver.h
@@ -108,6 +108,8 @@
Symbol *addUndefined(StringRef Sym);
+ StringRef mangleMaybe(Symbol *S);
+
// Windows specific -- "main" is not the only main function in Windows.
// You can choose one from these four -- {w,}{WinMain,main}.
// There are four different entry point functions for them,
diff --git a/COFF/DriverUtils.cpp b/COFF/DriverUtils.cpp
index f689cd1..c59027e 100644
--- a/COFF/DriverUtils.cpp
+++ b/COFF/DriverUtils.cpp
@@ -655,18 +655,6 @@
}
for (Export &E : Config->Exports) {
- Symbol *Sym = E.Sym;
- if (!E.ForwardTo.empty() || !Sym) {
- E.SymbolName = E.Name;
- } else {
- if (auto *U = dyn_cast<Undefined>(Sym))
- if (U->WeakAlias)
- Sym = U->WeakAlias;
- E.SymbolName = Sym->getName();
- }
- }
-
- for (Export &E : Config->Exports) {
if (!E.ForwardTo.empty()) {
E.ExportName = undecorate(E.Name);
} else {
diff --git a/COFF/SymbolTable.cpp b/COFF/SymbolTable.cpp
index 1c602c6..5180559 100644
--- a/COFF/SymbolTable.cpp
+++ b/COFF/SymbolTable.cpp
@@ -472,48 +472,56 @@
return find(Name);
}
-StringRef SymbolTable::findByPrefix(StringRef Prefix) {
+// Return all symbols that start with Prefix, possibly ignoring the first
+// character of Prefix or the first character symbol.
+std::vector<Symbol *> SymbolTable::getSymsWithPrefix(StringRef Prefix) {
+ std::vector<Symbol *> Syms;
for (auto Pair : SymMap) {
StringRef Name = Pair.first.val();
- if (Name.startswith(Prefix))
- return Name;
+ if (Name.startswith(Prefix) || Name.startswith(Prefix.drop_front()) ||
+ Name.drop_front().startswith(Prefix) ||
+ Name.drop_front().startswith(Prefix.drop_front())) {
+ Syms.push_back(Pair.second);
+ }
}
- return "";
+ return Syms;
}
-StringRef SymbolTable::findMangle(StringRef Name) {
+Symbol *SymbolTable::findMangle(StringRef Name) {
if (Symbol *Sym = find(Name))
if (!isa<Undefined>(Sym))
- return Name;
+ return Sym;
+
+ // Efficient fuzzy string lookup is impossible with a hash table, so iterate
+ // the symbol table once and collect all possibly matching symbols into this
+ // vector. Then compare each possibly matching symbol with each possible
+ // mangling.
+ std::vector<Symbol *> Syms = getSymsWithPrefix(Name);
+ auto FindByPrefix = [&Syms](const Twine &T) -> Symbol * {
+ std::string Prefix = T.str();
+ for (auto *S : Syms)
+ if (S->getName().startswith(Prefix))
+ return S;
+ return nullptr;
+ };
+
+ // For non-x86, just look for C++ functions.
if (Config->Machine != I386)
- return findByPrefix(("?" + Name + "@@Y").str());
+ return FindByPrefix("?" + Name + "@@Y");
+
if (!Name.startswith("_"))
- return "";
+ return nullptr;
// Search for x86 stdcall function.
- StringRef S = findByPrefix((Name + "@").str());
- if (!S.empty())
+ if (Symbol *S = FindByPrefix(Name + "@"))
return S;
// Search for x86 fastcall function.
- S = findByPrefix(("@" + Name.substr(1) + "@").str());
- if (!S.empty())
+ if (Symbol *S = FindByPrefix("@" + Name.substr(1) + "@"))
return S;
// Search for x86 vectorcall function.
- S = findByPrefix((Name.substr(1) + "@@").str());
- if (!S.empty())
+ if (Symbol *S = FindByPrefix(Name.substr(1) + "@@"))
return S;
// Search for x86 C++ non-member function.
- return findByPrefix(("?" + Name.substr(1) + "@@Y").str());
-}
-
-void SymbolTable::mangleMaybe(Symbol *B) {
- auto *U = dyn_cast<Undefined>(B);
- if (!U || U->WeakAlias)
- return;
- StringRef Alias = findMangle(U->getName());
- if (!Alias.empty()) {
- log(U->getName() + " aliased to " + Alias);
- U->WeakAlias = addUndefined(Alias);
- }
+ return FindByPrefix("?" + Name.substr(1) + "@@Y");
}
Symbol *SymbolTable::addUndefined(StringRef Name) {
diff --git a/COFF/SymbolTable.h b/COFF/SymbolTable.h
index 7f74863..d01bac1 100644
--- a/COFF/SymbolTable.h
+++ b/COFF/SymbolTable.h
@@ -68,8 +68,7 @@
// mangled symbol. This function tries to find a mangled name
// for U from the symbol table, and if found, set the symbol as
// a weak alias for U.
- void mangleMaybe(Symbol *B);
- StringRef findMangle(StringRef Name);
+ Symbol *findMangle(StringRef Name);
// Build a set of COFF objects representing the combined contents of
// BitcodeFiles and add them to the symbol table. Called after all files are
@@ -115,7 +114,8 @@
std::pair<Symbol *, bool> insert(StringRef Name);
/// Same as insert(Name), but also sets IsUsedInRegularObj.
std::pair<Symbol *, bool> insert(StringRef Name, InputFile *F);
- StringRef findByPrefix(StringRef Prefix);
+
+ std::vector<Symbol *> getSymsWithPrefix(StringRef Prefix);
llvm::DenseMap<llvm::CachedHashStringRef, Symbol *> SymMap;
std::unique_ptr<BitcodeCompiler> LTO;
diff --git a/test/COFF/export-stdcall.s b/test/COFF/export-stdcall.s
new file mode 100644
index 0000000..b114641
--- /dev/null
+++ b/test/COFF/export-stdcall.s
@@ -0,0 +1,31 @@
+# RUN: llvm-mc -triple i686-windows-msvc %s -o %t.obj -filetype=obj
+# RUN: lld-link %t.obj -out:%t.dll -dll -nodefaultlib -noentry -export:foo_std=bar_std -export:foo_fast=bar_fast
+# RUN: llvm-nm %t.lib | FileCheck %s
+
+# MSVC fudges the lookup of 'bar' to allow it to find the stdcall function
+# _bar_std@8, and then exports _foo_std@8. Same for fastcall and other mangling
+# schemes.
+
+# CHECK: export-stdcall.s.tmp.dll:
+# CHECK: 00000000 T @foo_fast@8
+# CHECK: 00000000 T __imp_@foo_fast@8
+
+# CHECK: export-stdcall.s.tmp.dll:
+# CHECK: 00000000 T __imp__foo_std@8
+# CHECK: 00000000 T _foo_std@8
+
+ .text
+ .def _bar_std@8; .scl 2; .type 32; .endef
+ .globl _bar_std@8
+_bar_std@8:
+ movl 8(%esp), %eax
+ movl 4(%esp), %ecx
+ leal 42(%ecx,%eax), %eax
+ retl $8
+
+ .def @bar_fast@8; .scl 2; .type 32; .endef
+ .globl @bar_fast@8
+@bar_fast@8:
+ leal 42(%ecx,%eax), %eax
+ retl
+
diff --git a/test/COFF/export-weak-alias.s b/test/COFF/export-weak-alias.s
new file mode 100644
index 0000000..d1c2141
--- /dev/null
+++ b/test/COFF/export-weak-alias.s
@@ -0,0 +1,32 @@
+# RUN: llvm-mc -triple x86_64-windows-msvc %s -o %t.obj -filetype=obj
+# RUN: lld-link %t.obj -out:%t.dll -dll -nodefaultlib -noentry
+# RUN: llvm-nm %t.lib | FileCheck %s
+
+# CHECK: export-weak-alias.s.tmp.dll:
+# CHECK: 00000000 T __imp_foo_dll{{$}}
+# CHECK: 00000000 T foo_dll{{$}}
+
+ .text
+ .def @feat.00;
+ .scl 3;
+ .type 0;
+ .endef
+ .globl @feat.00
+.set @feat.00, 0
+ .file "t.c"
+ .def foo_def;
+ .scl 2;
+ .type 32;
+ .endef
+ .globl foo_def # -- Begin function foo_def
+ .p2align 4, 0x90
+foo_def: # @foo_def
+# %bb.0: # %entry
+ movl $42, %eax
+ retq
+ # -- End function
+ .section .drectve,"yn"
+ .ascii " /alternatename:foo=foo_def"
+ .ascii " /export:foo_dll=foo"
+
+ .addrsig
