[lld] r340387 - Change how we handle -wrap.
Rui Ueyama via llvm-commits
llvm-commits at lists.llvm.org
Wed Aug 22 00:02:26 PDT 2018
Author: ruiu
Date: Wed Aug 22 00:02:26 2018
New Revision: 340387
URL: http://llvm.org/viewvc/llvm-project?rev=340387&view=rev
Log:
Change how we handle -wrap.
We have an issue with -wrap that the option doesn't work well when
renamed symbols get PLT entries. I'll explain what is the issue and
how this patch solves it.
For one -wrap option, we have three symbols: foo, wrap_foo and real_foo.
Currently, we use memcpy to overwrite wrapped symbols so that they get
the same contents. This works in most cases but doesn't when the relocation
processor sets some flags in the symbol. memcpy'ed symbols are just
aliases, so they always have to have the same contents, but the
relocation processor breaks that assumption.
r336609 is an attempt to fix the issue by memcpy'ing again after
processing relocations, so that symbols that are out of sync get the
same contents again. That works in most cases as well, but it breaks
ASan build in a mysterious way.
We could probably fix the issue by choosing symbol attributes that need
to be copied after they are updated. But it feels too complicated to me.
So, in this patch, I fixed it once and for all. With this patch, we no
longer memcpy symbols. All references to renamed symbols point to new
symbols after wrapSymbols() is done.
Differential Revision: https://reviews.llvm.org/D50569
Added:
lld/trunk/test/ELF/wrap-entry.s
lld/trunk/test/ELF/wrap-plt.s
Modified:
lld/trunk/ELF/Driver.cpp
lld/trunk/ELF/InputFiles.h
lld/trunk/ELF/SymbolTable.cpp
lld/trunk/ELF/SymbolTable.h
lld/trunk/ELF/Symbols.h
lld/trunk/test/ELF/lto/wrap-2.ll
lld/trunk/test/ELF/wrap-no-real.s
lld/trunk/test/ELF/wrap.s
Modified: lld/trunk/ELF/Driver.cpp
URL: http://llvm.org/viewvc/llvm-project/lld/trunk/ELF/Driver.cpp?rev=340387&r1=340386&r2=340387&view=diff
==============================================================================
--- lld/trunk/ELF/Driver.cpp (original)
+++ lld/trunk/ELF/Driver.cpp Wed Aug 22 00:02:26 2018
@@ -1325,6 +1325,80 @@ static void findKeepUniqueSections(opt::
}
}
+// The --wrap option is a feature to rename symbols so that you can write
+// wrappers for existing functions. If you pass `-wrap=foo`, all
+// occurrences of symbol `foo` are resolved to `wrap_foo` (so, you are
+// expected to write `wrap_foo` function as a wrapper). The original
+// symbol becomes accessible as `real_foo`, so you can call that from your
+// wrapper.
+//
+// This data structure is instantiated for each -wrap option.
+struct WrappedSymbol {
+ Symbol *Sym;
+ Symbol *Real;
+ Symbol *Wrap;
+};
+
+// Handles -wrap option.
+//
+// This function instantiates wrapper symbols. At this point, they seem
+// like they are not being used at all, so we explicitly set some flags so
+// that LTO won't eliminate them.
+template <class ELFT>
+static std::vector<WrappedSymbol> addWrappedSymbols(opt::InputArgList &Args) {
+ std::vector<WrappedSymbol> V;
+ DenseSet<StringRef> Seen;
+
+ for (auto *Arg : Args.filtered(OPT_wrap)) {
+ StringRef Name = Arg->getValue();
+ if (!Seen.insert(Name).second)
+ continue;
+
+ Symbol *Sym = Symtab->find(Name);
+ if (!Sym)
+ continue;
+
+ Symbol *Real = Symtab->addUndefined<ELFT>(Saver.save("__real_" + Name));
+ Symbol *Wrap = Symtab->addUndefined<ELFT>(Saver.save("__wrap_" + Name));
+ V.push_back({Sym, Real, Wrap});
+
+ // We want to tell LTO not to inline symbols to be overwritten
+ // because LTO doesn't know the final symbol contents after renaming.
+ Real->CanInline = false;
+ Sym->CanInline = false;
+
+ // Tell LTO not to eliminate these symbols.
+ Sym->IsUsedInRegularObj = true;
+ Wrap->IsUsedInRegularObj = true;
+ }
+ return V;
+}
+
+// Do renaming for -wrap by updating pointers to symbols.
+//
+// When this function is executed, only InputFiles and symbol table
+// contain pointers to symbol objects. We visit them to replace pointers,
+// so that wrapped symbols are swapped as instructed by the command line.
+template <class ELFT> static void wrapSymbols(ArrayRef<WrappedSymbol> Wrapped) {
+ DenseMap<Symbol *, Symbol *> Map;
+ for (const WrappedSymbol &W : Wrapped) {
+ Map[W.Sym] = W.Wrap;
+ Map[W.Real] = W.Sym;
+ }
+
+ // Update pointers in input files.
+ parallelForEach(ObjectFiles, [&](InputFile *File) {
+ std::vector<Symbol *> &Syms = File->getMutableSymbols();
+ for (size_t I = 0, E = Syms.size(); I != E; ++I)
+ if (Symbol *S = Map.lookup(Syms[I]))
+ Syms[I] = S;
+ });
+
+ // Update pointers in the symbol table.
+ for (const WrappedSymbol &W : Wrapped)
+ Symtab->wrap(W.Sym, W.Real, W.Wrap);
+}
+
static const char *LibcallRoutineNames[] = {
#define HANDLE_LIBCALL(code, name) name,
#include "llvm/IR/RuntimeLibcalls.def"
@@ -1456,8 +1530,7 @@ template <class ELFT> void LinkerDriver:
Symtab->scanVersionScript();
// Create wrapped symbols for -wrap option.
- for (auto *Arg : Args.filtered(OPT_wrap))
- Symtab->addSymbolWrap<ELFT>(Arg->getValue());
+ std::vector<WrappedSymbol> Wrapped = addWrappedSymbols<ELFT>(Args);
// Do link-time optimization if given files are LLVM bitcode files.
// This compiles bitcode files into real object files.
@@ -1475,7 +1548,8 @@ template <class ELFT> void LinkerDriver:
return;
// Apply symbol renames for -wrap.
- Symtab->applySymbolWrap();
+ if (!Wrapped.empty())
+ wrapSymbols<ELFT>(Wrapped);
// Now that we have a complete list of input files.
// Beyond this point, no new files are added.
Modified: lld/trunk/ELF/InputFiles.h
URL: http://llvm.org/viewvc/llvm-project/lld/trunk/ELF/InputFiles.h?rev=340387&r1=340386&r2=340387&view=diff
==============================================================================
--- lld/trunk/ELF/InputFiles.h (original)
+++ lld/trunk/ELF/InputFiles.h Wed Aug 22 00:02:26 2018
@@ -86,7 +86,9 @@ public:
// Returns object file symbols. It is a runtime error to call this
// function on files of other types.
- ArrayRef<Symbol *> getSymbols() {
+ ArrayRef<Symbol *> getSymbols() { return getMutableSymbols(); }
+
+ std::vector<Symbol *> &getMutableSymbols() {
assert(FileKind == BinaryKind || FileKind == ObjKind ||
FileKind == BitcodeKind);
return Symbols;
Modified: lld/trunk/ELF/SymbolTable.cpp
URL: http://llvm.org/viewvc/llvm-project/lld/trunk/ELF/SymbolTable.cpp?rev=340387&r1=340386&r2=340387&view=diff
==============================================================================
--- lld/trunk/ELF/SymbolTable.cpp (original)
+++ lld/trunk/ELF/SymbolTable.cpp Wed Aug 22 00:02:26 2018
@@ -152,64 +152,21 @@ void SymbolTable::trace(StringRef Name)
SymMap.insert({CachedHashStringRef(Name), -1});
}
-// Rename SYM as __wrap_SYM. The original symbol is preserved as __real_SYM.
-// Used to implement --wrap.
-template <class ELFT> void SymbolTable::addSymbolWrap(StringRef Name) {
- Symbol *Sym = find(Name);
- if (!Sym)
- return;
-
- // Do not wrap the same symbol twice.
- for (const WrappedSymbol &S : WrappedSymbols)
- if (S.Sym == Sym)
- return;
-
- Symbol *Real = addUndefined<ELFT>(Saver.save("__real_" + Name));
- Symbol *Wrap = addUndefined<ELFT>(Saver.save("__wrap_" + Name));
- WrappedSymbols.push_back({Sym, Real, Wrap});
-
- // We want to tell LTO not to inline symbols to be overwritten
- // because LTO doesn't know the final symbol contents after renaming.
- Real->CanInline = false;
- Sym->CanInline = false;
-
- // Tell LTO not to eliminate these symbols.
- Sym->IsUsedInRegularObj = true;
- Wrap->IsUsedInRegularObj = true;
-}
-
-// Apply symbol renames created by -wrap. The renames are created
-// before LTO in addSymbolWrap() to have a chance to inform LTO (if
-// LTO is running) not to include these symbols in IPO. Now that the
-// symbols are finalized, we can perform the replacement.
-void SymbolTable::applySymbolWrap() {
- // This function rotates 3 symbols:
- //
- // __real_sym becomes sym
- // sym becomes __wrap_sym
- // __wrap_sym becomes __real_sym
- //
- // The last part is special in that we don't want to change what references to
- // __wrap_sym point to, we just want have __real_sym in the symbol table.
-
- for (WrappedSymbol &W : WrappedSymbols) {
- // First, make a copy of __real_sym.
- Symbol *Real = nullptr;
- if (W.Real->isDefined()) {
- Real = reinterpret_cast<Symbol *>(make<SymbolUnion>());
- memcpy(Real, W.Real, sizeof(SymbolUnion));
- }
-
- // Replace __real_sym with sym and sym with __wrap_sym.
- memcpy(W.Real, W.Sym, sizeof(SymbolUnion));
- memcpy(W.Sym, W.Wrap, sizeof(SymbolUnion));
-
- // We now have two copies of __wrap_sym. Drop one.
- W.Wrap->IsUsedInRegularObj = false;
-
- if (Real)
- SymVector.push_back(Real);
- }
+void SymbolTable::wrap(Symbol *Sym, Symbol *Real, Symbol *Wrap) {
+ // Swap symbols as instructed by -wrap.
+ int &Idx1 = Symtab->SymMap[CachedHashStringRef(Sym->getName())];
+ int &Idx2 = Symtab->SymMap[CachedHashStringRef(Real->getName())];
+ int &Idx3 = Symtab->SymMap[CachedHashStringRef(Wrap->getName())];
+
+ Idx2 = Idx1;
+ Idx1 = Idx3;
+
+ // Now renaming is complete. No one refers Real symbol. We could leave
+ // Real as-is, but if Real is written to the symbol table, that may
+ // contain irrelevant values. So, we copy all values from Sym to Real.
+ StringRef S = Real->getName();
+ memcpy(Real, Sym, sizeof(SymbolUnion));
+ Real->setName(S);
}
static uint8_t getMinVisibility(uint8_t VA, uint8_t VB) {
@@ -822,11 +779,6 @@ template void SymbolTable::addFile<ELF32
template void SymbolTable::addFile<ELF64LE>(InputFile *);
template void SymbolTable::addFile<ELF64BE>(InputFile *);
-template void SymbolTable::addSymbolWrap<ELF32LE>(StringRef);
-template void SymbolTable::addSymbolWrap<ELF32BE>(StringRef);
-template void SymbolTable::addSymbolWrap<ELF64LE>(StringRef);
-template void SymbolTable::addSymbolWrap<ELF64BE>(StringRef);
-
template Symbol *SymbolTable::addUndefined<ELF32LE>(StringRef);
template Symbol *SymbolTable::addUndefined<ELF32BE>(StringRef);
template Symbol *SymbolTable::addUndefined<ELF64LE>(StringRef);
Modified: lld/trunk/ELF/SymbolTable.h
URL: http://llvm.org/viewvc/llvm-project/lld/trunk/ELF/SymbolTable.h?rev=340387&r1=340386&r2=340387&view=diff
==============================================================================
--- lld/trunk/ELF/SymbolTable.h (original)
+++ lld/trunk/ELF/SymbolTable.h Wed Aug 22 00:02:26 2018
@@ -37,8 +37,7 @@ class SymbolTable {
public:
template <class ELFT> void addFile(InputFile *File);
template <class ELFT> void addCombinedLTOObject();
- template <class ELFT> void addSymbolWrap(StringRef Name);
- void applySymbolWrap();
+ void wrap(Symbol *Sym, Symbol *Real, Symbol *Wrap);
ArrayRef<Symbol *> getSymbols() const { return SymVector; }
@@ -121,15 +120,6 @@ private:
// directive in version scripts.
llvm::Optional<llvm::StringMap<std::vector<Symbol *>>> DemangledSyms;
- struct WrappedSymbol {
- Symbol *Sym;
- Symbol *Real;
- Symbol *Wrap;
- };
-
- // For -wrap.
- std::vector<WrappedSymbol> WrappedSymbols;
-
// For LTO.
std::unique_ptr<BitcodeCompiler> LTO;
};
Modified: lld/trunk/ELF/Symbols.h
URL: http://llvm.org/viewvc/llvm-project/lld/trunk/ELF/Symbols.h?rev=340387&r1=340386&r2=340387&view=diff
==============================================================================
--- lld/trunk/ELF/Symbols.h (original)
+++ lld/trunk/ELF/Symbols.h Wed Aug 22 00:02:26 2018
@@ -137,6 +137,11 @@ public:
return {NameData, NameSize};
}
+ void setName(StringRef S) {
+ NameData = S.data();
+ NameSize = S.size();
+ }
+
void parseSymbolVersion();
bool isInGot() const { return GotIndex != -1U; }
Modified: lld/trunk/test/ELF/lto/wrap-2.ll
URL: http://llvm.org/viewvc/llvm-project/lld/trunk/test/ELF/lto/wrap-2.ll?rev=340387&r1=340386&r2=340387&view=diff
==============================================================================
--- lld/trunk/test/ELF/lto/wrap-2.ll (original)
+++ lld/trunk/test/ELF/lto/wrap-2.ll Wed Aug 22 00:02:26 2018
@@ -28,11 +28,15 @@
; THIN-NEXT: jmp{{.*}}<bar>
; Check that bar and __wrap_bar retain their original binding.
-; BIND: Name: __wrap_bar
+; BIND: Name: bar
; BIND-NEXT: Value:
; BIND-NEXT: Size:
; BIND-NEXT: Binding: Local
-; BIND: Name: bar
+; BIND: Name: __real_bar
+; BIND-NEXT: Value:
+; BIND-NEXT: Size:
+; BIND-NEXT: Binding: Local
+; BIND: Name: __wrap_bar
; BIND-NEXT: Value:
; BIND-NEXT: Size:
; BIND-NEXT: Binding: Local
Added: lld/trunk/test/ELF/wrap-entry.s
URL: http://llvm.org/viewvc/llvm-project/lld/trunk/test/ELF/wrap-entry.s?rev=340387&view=auto
==============================================================================
--- lld/trunk/test/ELF/wrap-entry.s (added)
+++ lld/trunk/test/ELF/wrap-entry.s Wed Aug 22 00:02:26 2018
@@ -0,0 +1,13 @@
+// REQUIRES: x86
+// RUN: llvm-mc -filetype=obj -triple=x86_64-pc-linux %s -o %t.o
+
+// RUN: ld.lld -o %t.exe %t.o -wrap=_start
+// RUN: llvm-readobj -file-headers %t.exe | FileCheck %s
+
+// CHECK: Entry: 0x201001
+
+.global _start, __wrap__start
+_start:
+ nop
+__wrap__start:
+ nop
Modified: lld/trunk/test/ELF/wrap-no-real.s
URL: http://llvm.org/viewvc/llvm-project/lld/trunk/test/ELF/wrap-no-real.s?rev=340387&r1=340386&r2=340387&view=diff
==============================================================================
--- lld/trunk/test/ELF/wrap-no-real.s (original)
+++ lld/trunk/test/ELF/wrap-no-real.s Wed Aug 22 00:02:26 2018
@@ -15,60 +15,15 @@
// CHECK-NEXT: movl $0x11010, %edx
// CHECK-NEXT: movl $0x11000, %edx
-// RUN: llvm-readobj -t %t | FileCheck -check-prefix=SYM %s
+// RUN: llvm-objdump -t %t | FileCheck -check-prefix=SYM %s
-// Test the full symbol table. It is verbose, but lld at times
-// produced duplicated symbols which are hard to test otherwise.
-// SYM: Symbols [
-// SYM-NEXT: Symbol {
-// SYM-NEXT: Name: (0)
-// SYM-NEXT: Value:
-// SYM-NEXT: Size:
-// SYM-NEXT: Binding:
-// SYM-NEXT: Type
-// SYM-NEXT: Other:
-// SYM-NEXT: Section:
-// SYM-NEXT: }
-// SYM-NEXT: Symbol {
-// SYM-NEXT: Name: _DYNAMIC
-// SYM-NEXT: Value:
-// SYM-NEXT: Size:
-// SYM-NEXT: Binding:
-// SYM-NEXT: Type:
-// SYM-NEXT: Other [
-// SYM-NEXT: STV_HIDDEN
-// SYM-NEXT: ]
-// SYM-NEXT: Section: .dynamic
-// SYM-NEXT: }
-// SYM-NEXT: Symbol {
-// SYM-NEXT: Name: foo
-// SYM-NEXT: Value: 0x11000
-// SYM-NEXT: Size:
-// SYM-NEXT: Binding:
-// SYM-NEXT: Type:
-// SYM-NEXT: Other:
-// SYM-NEXT: Section:
-// SYM-NEXT: }
-// SYM-NEXT: Symbol {
-// SYM-NEXT: Name: _start
-// SYM-NEXT: Value:
-// SYM-NEXT: Size:
-// SYM-NEXT: Binding:
-// SYM-NEXT: Type
-// SYM-NEXT: Other:
-// SYM-NEXT: Section:
-// SYM-NEXT: }
-// SYM-NEXT: Symbol {
-// SYM-NEXT: Name: __wrap_foo
-// SYM-NEXT: Value: 0x11010
-// SYM-NEXT: Size:
-// SYM-NEXT: Binding:
-// SYM-NEXT: Type:
-// SYM-NEXT: Other:
-// SYM-NEXT: Section:
-// SYM-NEXT: }
-// SYM-NEXT: ]
+// SYM: 0000000000000000 *UND* 00000000
+// SYM-NEXT: 0000000000202000 .dynamic 00000000 .hidden _DYNAMIC
+// SYM-NEXT: 0000000000011000 *ABS* 00000000 __real_foo
+// SYM-NEXT: 0000000000011010 *ABS* 00000000 __wrap_foo
+// SYM-NEXT: 0000000000201000 .text 00000000 _start
+// SYM-NEXT: 0000000000011000 *ABS* 00000000 foo
.global _start
_start:
Added: lld/trunk/test/ELF/wrap-plt.s
URL: http://llvm.org/viewvc/llvm-project/lld/trunk/test/ELF/wrap-plt.s?rev=340387&view=auto
==============================================================================
--- lld/trunk/test/ELF/wrap-plt.s (added)
+++ lld/trunk/test/ELF/wrap-plt.s Wed Aug 22 00:02:26 2018
@@ -0,0 +1,45 @@
+// REQUIRES: x86
+// RUN: llvm-mc -filetype=obj -triple=x86_64-pc-linux %s -o %t
+
+// RUN: ld.lld -o %t2 %t -wrap foo -shared
+// RUN: llvm-readobj -s -r %t2 | FileCheck %s
+// RUN: llvm-objdump -d %t2 | FileCheck --check-prefix=DISASM %s
+
+// CHECK: Name: .plt
+// CHECK-NEXT: Type: SHT_PROGBITS
+// CHECK-NEXT: Flags [
+// CHECK-NEXT: SHF_ALLOC
+// CHECK-NEXT: SHF_EXECINSTR
+// CHECK-NEXT: ]
+// CHECK-NEXT: Address: 0x1020
+// CHECK-NEXT: Offset:
+// CHECK-NEXT: Size: 48
+// CHECK-NEXT: Link: 0
+// CHECK-NEXT: Info: 0
+// CHECK-NEXT: AddressAlignment: 16
+
+// CHECK: Relocations [
+// CHECK-NEXT: Section ({{.*}}) .rela.plt {
+// CHECK-NEXT: 0x2018 R_X86_64_JUMP_SLOT __wrap_foo 0x0
+// CHECK-NEXT: 0x2020 R_X86_64_JUMP_SLOT _start 0x0
+// CHECK-NEXT: }
+// CHECK-NEXT: ]
+
+// DISASM: _start:
+// DISASM-NEXT: jmp 41
+// DISASM-NEXT: jmp 36
+// DISASM-NEXT: jmp 47
+
+.global foo
+foo:
+ nop
+
+.global __wrap_foo
+__wrap_foo:
+ nop
+
+.global _start
+_start:
+ jmp foo at plt
+ jmp __wrap_foo at plt
+ jmp _start at plt
Modified: lld/trunk/test/ELF/wrap.s
URL: http://llvm.org/viewvc/llvm-project/lld/trunk/test/ELF/wrap.s?rev=340387&r1=340386&r2=340387&view=diff
==============================================================================
--- lld/trunk/test/ELF/wrap.s (original)
+++ lld/trunk/test/ELF/wrap.s Wed Aug 22 00:02:26 2018
@@ -34,7 +34,7 @@
// SYM2-NEXT: STV_PROTECTED
// SYM2-NEXT: ]
// SYM3: Name: __real_foo
-// SYM3-NEXT: Value: 0x11020
+// SYM3-NEXT: Value: 0x11000
// SYM3-NEXT: Size:
// SYM3-NEXT: Binding: Global
// SYM3-NEXT: Type: None
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