Commit ab58e4cb authored by Sam Clegg's avatar Sam Clegg
Browse files

[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
parent 2518433f

lld/test/lit.cfg.py

+1 −2
Original line number Diff line number Diff line
@@ -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.

lld/test/wasm/data-segments.ll

+46 −1
Original line number Diff line number Diff line
@@ -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

lld/wasm/Driver.cpp

+1 −1
Original line number Diff line number Diff line
@@ -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

lld/wasm/SyntheticSections.cpp

+1 −1
Original line number Diff line number Diff line
@@ -372,7 +372,7 @@ void ExportSection::writeBody() { 
}



bool StartSection::isNeeded() const {

  return !config->relocatable && hasInitializedSegments && config->sharedMemory;

  return WasmSym::initMemory != nullptr;

}



void StartSection::writeBody() {

lld/wasm/Writer.cpp

+40 −10
Original line number Diff line number Diff line
@@ -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);

    // 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())