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[lld][WebAssembly] Add suppport for PIC + passive data initialization 

This change improves our support for shared memory to include
PIC executables (and shared libraries).

To handle this case the linker-generated `__wasm_init_memory`
function (that only exists in shared memory builds) must be
capable of loading memory segements at non-const offsets based
on the runtime value of `__memory_base`.

Differential Revision: https://reviews.llvm.org/D92620
This commit is contained in:
Sam Clegg 2020-12-03 16:51:56 -08:00
parent 2518433f86
commit ab58e4cb51
6 changed files with 90 additions and 15 deletions
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3
lld/test/lit.cfg.py
View File

@ -18,8 +18,7 @@ config.name = 'lld'
# testFormat: The test format to use to interpret tests.
#
# For now we require '&&' between commands, until they get globally killed and
# the test runner updated.
# For now we require '&&' between commands, until they get globally killed and the test runner updated.
config.test_format = lit.formats.ShTest(not llvm_config.use_lit_shell)
# suffixes: A list of file extensions to treat as test files.

47
lld/test/wasm/data-segments.ll
View File

@ -2,6 +2,8 @@
; RUN: llc --mtriple=wasm32-unknown-unknown -filetype=obj %s -o %t.bulk-mem.o -mattr=+bulk-memory
; RUN: llc --mtriple=wasm32-unknown-unknown -filetype=obj %s -o %t.atomics.bulk-mem.o -mattr=+atomics,+bulk-memory
; RUN: llc --mtriple=wasm64-unknown-unknown -filetype=obj %s -o %t.atomics.bulk-mem64.o -mattr=+atomics,+bulk-memory
; RUN: llc --mtriple=wasm32-unknown-unknown -filetype=obj %s -o %t.atomics.bulk-mem.pic.o -relocation-model=pic -mattr=+atomics,+bulk-memory,+mutable-globals
; RUN: llc --mtriple=wasm64-unknown-unknown -filetype=obj %s -o %t.atomics.bulk-mem.pic-mem64.o -relocation-model=pic -mattr=+atomics,+bulk-memory,+mutable-globals
; atomics, shared memory => error
; RUN: not wasm-ld -no-gc-sections --no-entry --shared-memory --max-memory=131072 %t.atomics.o -o %t.atomics.wasm 2>&1 | FileCheck %s --check-prefix ERROR
@ -19,8 +21,12 @@
; RUN: obj2yaml %t.atomics.bulk-mem64.wasm | FileCheck %s --check-prefixes PASSIVE,PASSIVE64
; Also test in combination with PIC/pie
; RUN: llc --mtriple=wasm32-unknown-unknown -filetype=obj -relocation-model=pic %s -o %t.atomics.bulk-mem.pic.o -mattr=+atomics,+bulk-memory,+mutable-globals
; RUN: wasm-ld --experimental-pic -pie -no-gc-sections --no-entry --shared-memory --max-memory=131072 %t.atomics.bulk-mem.pic.o -o %t.pic.wasm
; RUN: obj2yaml %t.pic.wasm | FileCheck %s --check-prefixes PASSIVE-PIC,PASSIVE32-PIC
; Also test in combination with PIC/pie + wasm64
; RUN: wasm-ld -mwasm64 --experimental-pic -pie -no-gc-sections --no-entry --shared-memory --max-memory=131072 %t.atomics.bulk-mem.pic-mem64.o -o %t.pic-mem64.wasm
; RUN: obj2yaml %t.pic-mem64.wasm | FileCheck %s --check-prefixes PASSIVE-PIC,PASSIVE64-PIC
@a = hidden global [6 x i8] c"hello\00", align 1
@b = hidden global [8 x i8] c"goodbye\00", align 1
@ -91,3 +97,42 @@
; PASSIVE-NEXT: Name: __wasm_init_memory
; PASSIVE-NEXT: - Index: 2
; PASSIVE-NEXT: Name: __wasm_init_tls
; PASSIVE-PIC: - Type: START
; PASSIVE-PIC-NEXT: StartFunction: 2
; PASSIVE-PIC-NEXT: - Type: DATACOUNT
; PASSIVE-PIC-NEXT: Count: 1
; PASSIVE-PIC-NEXT: - Type: CODE
; PASSIVE-PIC-NEXT: Functions:
; PASSIVE-PIC-NEXT: - Index: 0
; PASSIVE-PIC-NEXT: Locals: []
; PASSIVE-PIC-NEXT: Body: 10010B
; PASSIVE-PIC-NEXT: - Index: 1
; PASSIVE-PIC-NEXT: Locals: []
; PASSIVE-PIC-NEXT: Body: 0B
; PASSIVE-PIC-NEXT: - Index: 2
; PASSIVE-PIC-NEXT: Locals:
; PASSIVE32-PIC-NEXT: - Type: I32
; PASSIVE64-PIC-NEXT: - Type: I64
; PASSIVE-PIC-NEXT: Count: 1
; PASSIVE32-PIC-NEXT: Body: 230141B4CE006A2100200041004101FE480200044020004101427FFE0102001A05410023016A410041B1CE00FC08000020004102FE1702002000417FFE0002001A0BFC09000B
; PASSIVE64-PIC-NEXT: Body: 230142B4CE006A2100200041004101FE480200044020004101427FFE0102001A05420023016A410041B1CE00FC08000020004102FE1702002000417FFE0002001A0BFC09000B
; PASSIVE-PIC-NEXT: - Index: 3
; PASSIVE-PIC-NEXT: Locals: []
; PASSIVE-PIC-NEXT: Body: 0B
; PASSIVE-PIC-NEXT: - Type: DATA
; PASSIVE-PIC-NEXT: Segments:
; PASSIVE-PIC-NEXT: - SectionOffset: 4
; PASSIVE-PIC-NEXT: InitFlags: 1
; PASSIVE-PIC: - Type: CUSTOM
; PASSIVE-PIC-NEXT: Name: name
; PASSIVE-PIC-NEXT: FunctionNames:
; PASSIVE-PIC-NEXT: - Index: 0
; PASSIVE-PIC-NEXT: Name: __wasm_call_ctors
; PASSIVE-PIC-NEXT: - Index: 1
; PASSIVE-PIC-NEXT: Name: __wasm_apply_relocs
; PASSIVE-PIC-NEXT: - Index: 2
; PASSIVE-PIC-NEXT: Name: __wasm_init_memory
; PASSIVE-PIC-NEXT: - Index: 3
; PASSIVE-PIC-NEXT: Name: __wasm_init_tls

2
lld/wasm/Driver.cpp
View File

@ -645,7 +645,7 @@ static void createSyntheticSymbols() {
WasmSym::stackPointer->markLive();
}
if (config->sharedMemory && !config->shared) {
if (config->sharedMemory) {
// Passive segments are used to avoid memory being reinitialized on each
// thread's instantiation. These passive segments are initialized and
// dropped in __wasm_init_memory, which is registered as the start function

2
lld/wasm/SyntheticSections.cpp
View File

@ -372,7 +372,7 @@ void ExportSection::writeBody() {
}
bool StartSection::isNeeded() const {
return !config->relocatable && hasInitializedSegments && config->sharedMemory;
return WasmSym::initMemory != nullptr;
}
void StartSection::writeBody() {

50
lld/wasm/Writer.cpp
View File

@ -869,10 +869,24 @@ void Writer::createInitMemoryFunction() {
LLVM_DEBUG(dbgs() << "createInitMemoryFunction\n");
assert(WasmSym::initMemoryFlag);
uint64_t flagAddress = WasmSym::initMemoryFlag->getVirtualAddress();
bool is64 = config->is64.getValueOr(false);
std::string bodyContent;
{
raw_string_ostream os(bodyContent);
writeUleb128(os, 0, "num locals");
// With PIC code we cache the flag address in local 0
if (config->isPic) {
writeUleb128(os, 1, "num local decls");
writeUleb128(os, 1, "local count");
writeU8(os, is64 ? WASM_TYPE_I64 : WASM_TYPE_I32, "address type");
writeU8(os, WASM_OPCODE_GLOBAL_GET, "GLOBAL_GET");
writeUleb128(os, WasmSym::memoryBase->getGlobalIndex(), "memory_base");
writePtrConst(os, flagAddress, is64, "flag address");
writeU8(os, WASM_OPCODE_I32_ADD, "add");
writeU8(os, WASM_OPCODE_LOCAL_SET, "local.set");
writeUleb128(os, 0, "local 0");
} else {
writeUleb128(os, 0, "num locals");
}
if (hasPassiveInitializedSegments()) {
// Initialize memory in a thread-safe manner. The thread that successfully
@ -916,11 +930,24 @@ void Writer::createInitMemoryFunction() {
// )
// ( ... drop data segments ... )
// )
//
// When we are building with PIC, calculate the flag location using:
//
// (global.get $__memory_base)
// (i32.const $__init_memory_flag)
// (i32.const 1)
bool is64 = config->is64.getValueOr(false);
auto writeGetFlagAddress = [&]() {
if (config->isPic) {
writeU8(os, WASM_OPCODE_LOCAL_GET, "local.get");
writeUleb128(os, 0, "local 0");
} else {
writePtrConst(os, flagAddress, is64, "flag address");
}
};
// Atomically check whether this is the main thread.
writePtrConst(os, flagAddress, is64, "flag address");
writeGetFlagAddress();
writeI32Const(os, 0, "expected flag value");
writeI32Const(os, 1, "flag value");
writeU8(os, WASM_OPCODE_ATOMICS_PREFIX, "atomics prefix");
@ -930,7 +957,7 @@ void Writer::createInitMemoryFunction() {
writeU8(os, WASM_TYPE_NORESULT, "blocktype");
// Did not increment 0, so wait for main thread to initialize memory
writePtrConst(os, flagAddress, is64, "flag address");
writeGetFlagAddress();
writeI32Const(os, 1, "expected flag value");
writeI64Const(os, -1, "timeout");
@ -946,6 +973,12 @@ void Writer::createInitMemoryFunction() {
if (needsPassiveInitialization(s)) {
// destination address
writePtrConst(os, s->startVA, is64, "destination address");
if (config->isPic) {
writeU8(os, WASM_OPCODE_GLOBAL_GET, "GLOBAL_GET");
writeUleb128(os, WasmSym::memoryBase->getGlobalIndex(),
"memory_base");
writeU8(os, WASM_OPCODE_I32_ADD, "i32.add");
}
// source segment offset
writeI32Const(os, 0, "segment offset");
// memory region size
@ -959,14 +992,14 @@ void Writer::createInitMemoryFunction() {
}
// Set flag to 2 to mark end of initialization
writePtrConst(os, flagAddress, is64, "flag address");
writeGetFlagAddress();
writeI32Const(os, 2, "flag value");
writeU8(os, WASM_OPCODE_ATOMICS_PREFIX, "atomics prefix");
writeUleb128(os, WASM_OPCODE_I32_ATOMIC_STORE, "i32.atomic.store");
writeMemArg(os, 2, 0);
// Notify any waiters that memory initialization is complete
writePtrConst(os, flagAddress, is64, "flag address");
writeGetFlagAddress();
writeI32Const(os, -1, "number of waiters");
writeU8(os, WASM_OPCODE_ATOMICS_PREFIX, "atomics prefix");
writeUleb128(os, WASM_OPCODE_ATOMIC_NOTIFY, "atomic.notify");
@ -1095,9 +1128,6 @@ void Writer::createCommandExportWrapper(uint32_t functionIndex,
}
void Writer::createInitTLSFunction() {
if (!WasmSym::initTLS->isLive())
return;
std::string bodyContent;
{
raw_string_ostream os(bodyContent);
@ -1244,7 +1274,7 @@ void Writer::run() {
}
}
if (!config->relocatable && config->sharedMemory && !config->shared)
if (WasmSym::initTLS && WasmSym::initTLS->isLive())
createInitTLSFunction();
if (errorCount())

1
llvm/include/llvm/BinaryFormat/Wasm.h
View File

@ -263,6 +263,7 @@ enum : unsigned {
WASM_OPCODE_END = 0x0b,
WASM_OPCODE_CALL = 0x10,
WASM_OPCODE_LOCAL_GET = 0x20,
WASM_OPCODE_LOCAL_SET = 0x21,
WASM_OPCODE_GLOBAL_GET = 0x23,
WASM_OPCODE_GLOBAL_SET = 0x24,
WASM_OPCODE_I32_STORE = 0x36,