[lld] r357022 - [WebAssembly] Initial implementation of PIC code generation
Sam Clegg via llvm-commits
llvm-commits at lists.llvm.org
Tue Mar 26 12:46:15 PDT 2019
Author: sbc
Date: Tue Mar 26 12:46:15 2019
New Revision: 357022
URL: http://llvm.org/viewvc/llvm-project?rev=357022&view=rev
Log:
[WebAssembly] Initial implementation of PIC code generation
This change implements lowering of references global symbols in PIC
mode.
This change implements lowering of global references in PIC mode using a
new @GOT reference type. @GOT references can be used with function or
data symbol names combined with the get_global instruction. In this case
the linker will insert the wasm global that stores the address of the
symbol (either in memory for data symbols or in the wasm table for
function symbols).
For now I'm continuing to use the R_WASM_GLOBAL_INDEX_LEB relocation
type for this type of reference which means that this relocation type
can refer to either a global or a function or data symbol. We could
choose to introduce specific relocation types for GOT entries in the
future. See the current dynamic linking proposal:
https://github.com/WebAssembly/tool-conventions/blob/master/DynamicLinking.md
Differential Revision: https://reviews.llvm.org/D54647
Modified:
lld/trunk/test/wasm/shared.ll
lld/trunk/wasm/Driver.cpp
lld/trunk/wasm/InputChunks.cpp
lld/trunk/wasm/InputFiles.cpp
lld/trunk/wasm/Symbols.cpp
lld/trunk/wasm/Symbols.h
lld/trunk/wasm/Writer.cpp
Modified: lld/trunk/test/wasm/shared.ll
URL: http://llvm.org/viewvc/llvm-project/lld/trunk/test/wasm/shared.ll?rev=357022&r1=357021&r2=357022&view=diff
==============================================================================
--- lld/trunk/test/wasm/shared.ll (original)
+++ lld/trunk/test/wasm/shared.ll Tue Mar 26 12:46:15 2019
@@ -1,10 +1,11 @@
-; RUN: llc -O0 -filetype=obj %s -o %t.o
+; RUN: llc -relocation-model=pic -filetype=obj %s -o %t.o
; RUN: wasm-ld -shared -o %t.wasm %t.o
; RUN: obj2yaml %t.wasm | FileCheck %s
target triple = "wasm32-unknown-unknown"
@data = hidden global i32 2, align 4
+ at data_external = external global i32
@indirect_func = local_unnamed_addr global i32 ()* @foo, align 4
@indirect_func_external = local_unnamed_addr global void ()* @func_external, align 4
@@ -13,18 +14,22 @@ entry:
; To ensure we use __stack_pointer
%ptr = alloca i32
%0 = load i32, i32* @data, align 4
- ; TODO(sbc): Re-enable once the codegen supports generating the correct
- ; relocation type when referencing external data in shared libraries.
- ; %1 = load i32, i32* @data_external, align 4
%1 = load i32 ()*, i32 ()** @indirect_func, align 4
call i32 %1()
ret i32 %0
}
-declare void @func_external()
+define default i32* @get_data_address() {
+entry:
+ ret i32* @data_external
+}
- at data_external = external global i32
+define default i8* @get_func_address() {
+entry:
+ ret i8* bitcast (void ()* @func_external to i8*)
+}
+declare void @func_external()
; check for dylink section at start
@@ -43,6 +48,11 @@ declare void @func_external()
; CHECK: - Type: IMPORT
; CHECK-NEXT: Imports:
; CHECK-NEXT: - Module: env
+; CHECK-NEXT: Field: memory
+; CHECK-NEXT: Kind: MEMORY
+; CHECK-NEXT: Memory:
+; CHECK-NEXT: Initial: 0x0000000
+; CHECK-NEXT: - Module: env
; CHECK-NEXT: Field: __indirect_function_table
; CHECK-NEXT: Kind: TABLE
; CHECK-NEXT: Table:
@@ -64,15 +74,21 @@ declare void @func_external()
; CHECK-NEXT: Kind: GLOBAL
; CHECK-NEXT: GlobalType: I32
; CHECK-NEXT: GlobalMutable: false
-; XCHECK-NEXT: - Module: env
-; XCHECK-NEXT: Field: data_external
-; XCHECK-NEXT: Kind: GLOBAL
-; XCHECK-NEXT: GlobalType: I32
-; XCHECK-NEXT: GlobalMutable: true
; CHECK-NEXT: - Module: env
; CHECK-NEXT: Field: func_external
; CHECK-NEXT: Kind: FUNCTION
; CHECK-NEXT: SigIndex: 1
+; CHECK-NEXT: - Module: GOT.mem
+; CHECK-NEXT: Field: data_external
+; CHECK-NEXT: Kind: GLOBAL
+; CHECK-NEXT: GlobalType: I32
+; CHECK-NEXT: GlobalMutable: true
+; CHECK-NEXT: - Module: GOT.func
+; CHECK-NEXT: Field: func_external
+; CHECK-NEXT: Kind: GLOBAL
+; CHECK-NEXT: GlobalType: I32
+; CHECK-NEXT: GlobalMutable: true
+; CHECK-NEXT: - Type: FUNCTION
; check for elem segment initialized with __table_base global as offset
Modified: lld/trunk/wasm/Driver.cpp
URL: http://llvm.org/viewvc/llvm-project/lld/trunk/wasm/Driver.cpp?rev=357022&r1=357021&r2=357022&view=diff
==============================================================================
--- lld/trunk/wasm/Driver.cpp (original)
+++ lld/trunk/wasm/Driver.cpp Tue Mar 26 12:46:15 2019
@@ -519,6 +519,7 @@ void LinkerDriver::link(ArrayRef<const c
}
if (Config->Shared) {
+ Config->ImportMemory = true;
Config->ExportDynamic = true;
Config->AllowUndefined = true;
}
Modified: lld/trunk/wasm/InputChunks.cpp
URL: http://llvm.org/viewvc/llvm-project/lld/trunk/wasm/InputChunks.cpp?rev=357022&r1=357021&r2=357022&view=diff
==============================================================================
--- lld/trunk/wasm/InputChunks.cpp (original)
+++ lld/trunk/wasm/InputChunks.cpp Tue Mar 26 12:46:15 2019
@@ -74,11 +74,14 @@ void InputChunk::verifyRelocTargets() co
if (BytesRead && BytesRead != 5)
warn("expected LEB at relocation site be 5-byte padded");
- uint32_t ExpectedValue = File->calcExpectedValue(Rel);
- if (ExpectedValue != ExistingValue)
- warn("unexpected existing value for " + reloctTypeToString(Rel.Type) +
- ": existing=" + Twine(ExistingValue) +
- " expected=" + Twine(ExpectedValue));
+
+ if (Rel.Type != R_WASM_GLOBAL_INDEX_LEB) {
+ uint32_t ExpectedValue = File->calcExpectedValue(Rel);
+ if (ExpectedValue != ExistingValue)
+ warn("unexpected existing value for " + reloctTypeToString(Rel.Type) +
+ ": existing=" + Twine(ExistingValue) +
+ " expected=" + Twine(ExpectedValue));
+ }
}
}
Modified: lld/trunk/wasm/InputFiles.cpp
URL: http://llvm.org/viewvc/llvm-project/lld/trunk/wasm/InputFiles.cpp?rev=357022&r1=357021&r2=357022&view=diff
==============================================================================
--- lld/trunk/wasm/InputFiles.cpp (original)
+++ lld/trunk/wasm/InputFiles.cpp Tue Mar 26 12:46:15 2019
@@ -152,9 +152,12 @@ uint32_t ObjFile::calcNewValue(const Was
return TypeMap[Reloc.Index];
case R_WASM_FUNCTION_INDEX_LEB:
return getFunctionSymbol(Reloc.Index)->getFunctionIndex();
- case R_WASM_GLOBAL_INDEX_LEB:
- return getGlobalSymbol(Reloc.Index)->getGlobalIndex();
- case R_WASM_EVENT_INDEX_LEB:
+ case R_WASM_GLOBAL_INDEX_LEB: {
+ const Symbol* Sym = Symbols[Reloc.Index];
+ if (auto GS = dyn_cast<GlobalSymbol>(Sym))
+ return GS->getGlobalIndex();
+ return Sym->getGOTIndex();
+ } case R_WASM_EVENT_INDEX_LEB:
return getEventSymbol(Reloc.Index)->getEventIndex();
case R_WASM_FUNCTION_OFFSET_I32:
if (auto *Sym = dyn_cast<DefinedFunction>(getFunctionSymbol(Reloc.Index))) {
Modified: lld/trunk/wasm/Symbols.cpp
URL: http://llvm.org/viewvc/llvm-project/lld/trunk/wasm/Symbols.cpp?rev=357022&r1=357021&r2=357022&view=diff
==============================================================================
--- lld/trunk/wasm/Symbols.cpp (original)
+++ lld/trunk/wasm/Symbols.cpp Tue Mar 26 12:46:15 2019
@@ -93,6 +93,12 @@ void Symbol::setOutputSymbolIndex(uint32
OutputSymbolIndex = Index;
}
+void Symbol::setGOTIndex(uint32_t Index) {
+ LLVM_DEBUG(dbgs() << "setGOTIndex " << Name << " -> " << Index << "\n");
+ assert(GOTIndex == INVALID_INDEX);
+ GOTIndex = Index;
+}
+
bool Symbol::isWeak() const {
return (Flags & WASM_SYMBOL_BINDING_MASK) == WASM_SYMBOL_BINDING_WEAK;
}
Modified: lld/trunk/wasm/Symbols.h
URL: http://llvm.org/viewvc/llvm-project/lld/trunk/wasm/Symbols.h?rev=357022&r1=357021&r2=357022&view=diff
==============================================================================
--- lld/trunk/wasm/Symbols.h (original)
+++ lld/trunk/wasm/Symbols.h Tue Mar 26 12:46:15 2019
@@ -113,6 +113,16 @@ public:
const WasmSignature* getSignature() const;
+ bool isInGOT() const { return GOTIndex != INVALID_INDEX; }
+
+ uint32_t getGOTIndex() const {
+ assert(GOTIndex != INVALID_INDEX);
+ return GOTIndex;
+ }
+
+ void setGOTIndex(uint32_t Index);
+ bool hasGOTIndex() const { return GOTIndex != INVALID_INDEX; }
+
protected:
Symbol(StringRef Name, Kind K, uint32_t Flags, InputFile *F)
: IsUsedInRegularObj(false), ForceExport(false), Traced(false),
@@ -124,6 +134,7 @@ protected:
uint32_t Flags;
InputFile *File;
uint32_t OutputSymbolIndex = INVALID_INDEX;
+ uint32_t GOTIndex = INVALID_INDEX;
bool Referenced;
};
@@ -249,21 +260,6 @@ public:
static bool classof(const Symbol *S) {
return S->kind() == UndefinedDataKind;
}
-
- // Undefined data symbols are imported as wasm globals so also have a global
- // index.
- uint32_t getGlobalIndex() const {
- assert(GlobalIndex != INVALID_INDEX);
- return GlobalIndex;
- }
- void setGlobalIndex(uint32_t Index) {
- assert(GlobalIndex == INVALID_INDEX);
- GlobalIndex = Index;
- }
- bool hasGlobalIndex() const { return GlobalIndex != INVALID_INDEX; }
-
-protected:
- uint32_t GlobalIndex = INVALID_INDEX;
};
class GlobalSymbol : public Symbol {
Modified: lld/trunk/wasm/Writer.cpp
URL: http://llvm.org/viewvc/llvm-project/lld/trunk/wasm/Writer.cpp?rev=357022&r1=357021&r2=357022&view=diff
==============================================================================
--- lld/trunk/wasm/Writer.cpp (original)
+++ lld/trunk/wasm/Writer.cpp Tue Mar 26 12:46:15 2019
@@ -118,6 +118,7 @@ private:
std::vector<const WasmSignature *> Types;
DenseMap<WasmSignature, int32_t> TypeIndices;
std::vector<const Symbol *> ImportedSymbols;
+ std::vector<const Symbol *> GOTSymbols;
unsigned NumImportedFunctions = 0;
unsigned NumImportedGlobals = 0;
unsigned NumImportedEvents = 0;
@@ -147,7 +148,7 @@ private:
} // anonymous namespace
void Writer::createImportSection() {
- uint32_t NumImports = ImportedSymbols.size();
+ uint32_t NumImports = ImportedSymbols.size() + GOTSymbols.size();
if (Config->ImportMemory)
++NumImports;
if (Config->ImportTable)
@@ -204,9 +205,6 @@ void Writer::createImportSection() {
if (auto *FunctionSym = dyn_cast<FunctionSymbol>(Sym)) {
Import.Kind = WASM_EXTERNAL_FUNCTION;
Import.SigIndex = lookupType(*FunctionSym->Signature);
- } else if (auto *DataSym = dyn_cast<UndefinedData>(Sym)) {
- Import.Kind = WASM_EXTERNAL_GLOBAL;
- Import.Global = {WASM_TYPE_I32, true};
} else if (auto *GlobalSym = dyn_cast<GlobalSymbol>(Sym)) {
Import.Kind = WASM_EXTERNAL_GLOBAL;
Import.Global = *GlobalSym->getGlobalType();
@@ -218,6 +216,18 @@ void Writer::createImportSection() {
}
writeImport(OS, Import);
}
+
+ for (const Symbol *Sym : GOTSymbols) {
+ WasmImport Import;
+ Import.Kind = WASM_EXTERNAL_GLOBAL;
+ Import.Global = {WASM_TYPE_I32, true};
+ if (isa<DataSymbol>(Sym))
+ Import.Module = "GOT.mem";
+ else
+ Import.Module = "GOT.func";
+ Import.Field = Sym->getName();
+ writeImport(OS, Import);
+ }
}
void Writer::createTypeSection() {
@@ -957,9 +967,9 @@ void Writer::calculateImports() {
continue;
if (!Sym->IsUsedInRegularObj)
continue;
- // In relocatable output we don't generate imports for data symbols.
- // These live only in the symbol table.
- if (Config->Relocatable && isa<DataSymbol>(Sym))
+ // We don't generate imports for data symbols. They however can be imported
+ // as GOT entries.
+ if (isa<DataSymbol>(Sym))
continue;
LLVM_DEBUG(dbgs() << "import: " << Sym->getName() << "\n");
@@ -968,8 +978,6 @@ void Writer::calculateImports() {
F->setFunctionIndex(NumImportedFunctions++);
else if (auto *G = dyn_cast<GlobalSymbol>(Sym))
G->setGlobalIndex(NumImportedGlobals++);
- else if (auto *D = dyn_cast<UndefinedData>(Sym))
- D->setGlobalIndex(NumImportedGlobals++);
else
cast<EventSymbol>(Sym)->setEventIndex(NumImportedEvents++);
}
@@ -1145,6 +1153,13 @@ void Writer::processRelocations(InputChu
DataSym->getName());
break;
}
+ case R_WASM_GLOBAL_INDEX_LEB: {
+ auto* Sym = File->getSymbols()[Reloc.Index];
+ if (!isa<GlobalSymbol>(Sym) && !Sym->isInGOT()) {
+ Sym->setGOTIndex(NumImportedGlobals++);
+ GOTSymbols.push_back(Sym);
+ }
+ }
}
}
}
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