From: Sam Clegg Date: Sat, 15 Jan 2022 23:33:02 +0000 (-0800) Subject: [lld][WebAssembly] Perform data relocations during start function X-Git-Tag: upstream/15.0.7~20030 X-Git-Url: http://review.tizen.org/git/?a=commitdiff_plain;h=ec47dba1c8a2c89ae3ee3cfa052f69dc5fda153d;p=platform%2Fupstream%2Fllvm.git [lld][WebAssembly] Perform data relocations during start function We already perform memory initialization and apply global relocations during start. It makes sense to performs data relocations too. I think the reason we were not doing this already is solely historical. Differential Revision: https://reviews.llvm.org/D117412 --- diff --git a/lld/test/wasm/data-segments.ll b/lld/test/wasm/data-segments.ll index 7759386..be526de 100644 --- a/lld/test/wasm/data-segments.ll +++ b/lld/test/wasm/data-segments.ll @@ -115,7 +115,7 @@ ; PASSIVE-PIC-NEXT: Functions: ; PASSIVE-PIC-NEXT: - Index: 0 ; PASSIVE-PIC-NEXT: Locals: [] -; PASSIVE-PIC-NEXT: Body: 10030B +; PASSIVE-PIC-NEXT: Body: 0B ; PASSIVE-PIC-NEXT: - Index: 1 ; PASSIVE-PIC-NEXT: Locals: [] ; PASSIVE-PIC-NEXT: Body: 0B @@ -195,6 +195,8 @@ ; DIS-NEXT: i32.const 10000 ; DIS-NEXT: memory.fill 0 +; PIC-DIS-NEXT: call 3 + ; NOPIC-DIS-NEXT: [[PTR]].const 11060 ; PIC-DIS-NEXT: local.get 0 diff --git a/lld/test/wasm/pie.ll b/lld/test/wasm/pie.ll index 71af920..40159e7 100644 --- a/lld/test/wasm/pie.ll +++ b/lld/test/wasm/pie.ll @@ -1,6 +1,7 @@ ; RUN: llc -relocation-model=pic -mattr=+mutable-globals -filetype=obj %s -o %t.o ; RUN: wasm-ld --no-gc-sections --experimental-pic -pie -o %t.wasm %t.o ; RUN: obj2yaml %t.wasm | FileCheck %s +; RUN: llvm-objdump --disassemble-symbols=__wasm_start --no-show-raw-insn --no-leading-addr %t.wasm | FileCheck %s --check-prefixes DISASSEM target triple = "wasm32-unknown-emscripten" @@ -69,7 +70,7 @@ declare void @external_func() ; CHECK-NEXT: GlobalMutable: false ; CHECK: - Type: START -; CHECK-NEXT: StartFunction: 3 +; CHECK-NEXT: StartFunction: 4 ; CHECK: - Type: CUSTOM ; CHECK-NEXT: Name: name @@ -82,7 +83,14 @@ declare void @external_func() ; CHECK-NEXT: Name: __wasm_apply_data_relocs ; CHECK-NEXT: - Index: 3 ; CHECK-NEXT: Name: __wasm_apply_global_relocs +; CHECK-NEXT: - Index: 4 +; CHECK-NEXT: Name: __wasm_start +; DISASSEM: <__wasm_start>: +; DISASSEM-EMPTY: +; DISASSEM-NEXT: call 2 +; DISASSEM-NEXT: call 3 +; DISASSEM-NEXT: end ; Run the same test with threading support. In this mode ; we expect __wasm_init_memory and __wasm_apply_data_relocs @@ -92,11 +100,16 @@ declare void @external_func() ; RUN: llc -relocation-model=pic -mattr=+mutable-globals,+atomics,+bulk-memory -filetype=obj %s -o %t.shmem.o ; RUN: wasm-ld --no-gc-sections --shared-memory --allow-undefined --experimental-pic -pie -o %t.shmem.wasm %t.shmem.o ; RUN: obj2yaml %t.shmem.wasm | FileCheck %s --check-prefix=SHMEM +; RUN: llvm-objdump --disassemble-symbols=__wasm_start --no-show-raw-insn --no-leading-addr %t.shmem.wasm | FileCheck %s --check-prefixes DISASSEM-SHMEM -; SHMEM: - Type: CODE -; SHMEM: - Index: 6 -; SHMEM-NEXT: Locals: [] -; SHMEM-NEXT: Body: 100310050B +; SHMEM: - Type: START +; SHMEM-NEXT: StartFunction: 6 + +; DISASSEM-SHMEM: <__wasm_start>: +; DISASSEM-SHMEM-EMPTY: +; DISASSEM-SHMEM-NEXT: call 3 +; DISASSEM-SHMEM-NEXT: call 5 +; DISASSEM-SHMEM-NEXT: end ; SHMEM: FunctionNames: ; SHMEM-NEXT: - Index: 0 diff --git a/lld/wasm/Writer.cpp b/lld/wasm/Writer.cpp index f1ebe54..f7589b2 100644 --- a/lld/wasm/Writer.cpp +++ b/lld/wasm/Writer.cpp @@ -1022,7 +1022,16 @@ void Writer::createSyntheticInitFunctions() { } } - if (WasmSym::applyGlobalRelocs && WasmSym::initMemory) { + int startCount = 0; + if (WasmSym::applyGlobalRelocs) + startCount++; + if (WasmSym::WasmSym::initMemory || WasmSym::applyDataRelocs) + startCount++; + + // If there is only one start function we can just use that function + // itself as the Wasm start function, otherwise we need to synthesize + // a new function to call them in sequence. + if (startCount > 1) { WasmSym::startFunction = symtab->addSyntheticFunction( "__wasm_start", WASM_SYMBOL_VISIBILITY_HIDDEN, make(nullSignature, "__wasm_start")); @@ -1179,6 +1188,14 @@ void Writer::createInitMemoryFunction() { } } + // Memory init is now complete. Apply data relocation if there + // are any. + if (WasmSym::applyDataRelocs) { + writeU8(os, WASM_OPCODE_CALL, "CALL"); + writeUleb128(os, WasmSym::applyDataRelocs->getFunctionIndex(), + "function index"); + } + if (config->sharedMemory) { // Set flag to 2 to mark end of initialization writeGetFlagAddress(); @@ -1231,17 +1248,28 @@ void Writer::createInitMemoryFunction() { } void Writer::createStartFunction() { + // If the start function exists when we have more than one function to call. if (WasmSym::startFunction) { std::string bodyContent; { raw_string_ostream os(bodyContent); writeUleb128(os, 0, "num locals"); - writeU8(os, WASM_OPCODE_CALL, "CALL"); - writeUleb128(os, WasmSym::initMemory->getFunctionIndex(), - "function index"); - writeU8(os, WASM_OPCODE_CALL, "CALL"); - writeUleb128(os, WasmSym::applyGlobalRelocs->getFunctionIndex(), - "function index"); + if (WasmSym::initMemory) { + writeU8(os, WASM_OPCODE_CALL, "CALL"); + writeUleb128(os, WasmSym::initMemory->getFunctionIndex(), + "function index"); + } else if (WasmSym::applyDataRelocs) { + // When initMemory is present it calls applyDataRelocs. If not, + // we must call it directly. + writeU8(os, WASM_OPCODE_CALL, "CALL"); + writeUleb128(os, WasmSym::applyDataRelocs->getFunctionIndex(), + "function index"); + } + if (WasmSym::applyGlobalRelocs) { + writeU8(os, WASM_OPCODE_CALL, "CALL"); + writeUleb128(os, WasmSym::applyGlobalRelocs->getFunctionIndex(), + "function index"); + } writeU8(os, WASM_OPCODE_END, "END"); } createFunction(WasmSym::startFunction, bodyContent); @@ -1249,6 +1277,8 @@ void Writer::createStartFunction() { WasmSym::startFunction = WasmSym::initMemory; } else if (WasmSym::applyGlobalRelocs) { WasmSym::startFunction = WasmSym::applyGlobalRelocs; + } else if (WasmSym::applyDataRelocs) { + WasmSym::startFunction = WasmSym::applyDataRelocs; } } @@ -1311,8 +1341,7 @@ void Writer::createCallCtorsFunction() { // If __wasm_call_ctors isn't referenced, there aren't any ctors, and we // aren't calling `__wasm_apply_data_relocs` for Emscripten-style PIC, don't // define the `__wasm_call_ctors` function. - if (!WasmSym::callCtors->isLive() && !WasmSym::applyDataRelocs && - initFunctions.empty()) + if (!WasmSym::callCtors->isLive() && initFunctions.empty()) return; // First write the body's contents to a string. @@ -1321,7 +1350,7 @@ void Writer::createCallCtorsFunction() { raw_string_ostream os(bodyContent); writeUleb128(os, 0, "num locals"); - if (WasmSym::applyDataRelocs) { + if (WasmSym::applyDataRelocs && !WasmSym::initMemory) { writeU8(os, WASM_OPCODE_CALL, "CALL"); writeUleb128(os, WasmSym::applyDataRelocs->getFunctionIndex(), "function index");