mirror of
https://github.com/capstone-engine/llvm-capstone.git
synced 2024-12-03 19:32:35 +00:00
0362633fd2
In this initial version we only GC symbols with `hidden` visibility since other symbols we export to the embedder. We could potentially modify this the future and only use symbols explicitly passed via `--export` as GC roots. This version of the code only does GC of data and code. GC for the types section is coming soon. Differential Revision: https://reviews.llvm.org/D42511 llvm-svn: 323842
108 lines
3.3 KiB
C++
108 lines
3.3 KiB
C++
//===- MarkLive.cpp -------------------------------------------------------===//
|
|
//
|
|
// The LLVM Linker
|
|
//
|
|
// This file is distributed under the University of Illinois Open Source
|
|
// License. See LICENSE.TXT for details.
|
|
//
|
|
//===----------------------------------------------------------------------===//
|
|
//
|
|
// This file implements --gc-sections, which is a feature to remove unused
|
|
// chunks from the output. Unused chunks are those that are not reachable from
|
|
// known root symbols or chunks. This feature is implemented as a mark-sweep
|
|
// garbage collector.
|
|
//
|
|
// Here's how it works. Each InputChunk has a "Live" bit. The bit is off by
|
|
// default. Starting with the GC-roots, visit all reachable chunks and set their
|
|
// Live bits. The Writer will then ignore chunks whose Live bits are off, so
|
|
// that such chunk are not appear in the output.
|
|
//
|
|
//===----------------------------------------------------------------------===//
|
|
|
|
#include "MarkLive.h"
|
|
#include "Config.h"
|
|
#include "InputChunks.h"
|
|
#include "SymbolTable.h"
|
|
#include "Symbols.h"
|
|
|
|
#define DEBUG_TYPE "lld"
|
|
|
|
using namespace llvm;
|
|
using namespace llvm::wasm;
|
|
using namespace lld;
|
|
using namespace lld::wasm;
|
|
|
|
void lld::wasm::markLive() {
|
|
if (!Config->GcSections)
|
|
return;
|
|
|
|
DEBUG(dbgs() << "markLive\n");
|
|
SmallVector<InputChunk *, 256> Q;
|
|
|
|
auto Enqueue = [&](Symbol *Sym) {
|
|
if (!Sym)
|
|
return;
|
|
InputChunk *Chunk = Sym->getChunk();
|
|
if (!Chunk || Chunk->Live)
|
|
return;
|
|
Chunk->Live = true;
|
|
Q.push_back(Chunk);
|
|
};
|
|
|
|
// Add GC root symbols.
|
|
if (!Config->Entry.empty())
|
|
Enqueue(Symtab->find(Config->Entry));
|
|
Enqueue(Config->CtorSymbol);
|
|
|
|
// By default we export all non-hidden, so they are gc roots too
|
|
for (Symbol *Sym : Symtab->getSymbols())
|
|
if (!Sym->isHidden())
|
|
Enqueue(Sym);
|
|
|
|
// The ctor fuctions are all used the synthetic __wasm_call_ctors function,
|
|
// but since this function is created in-place it doesn't contain reloctations
|
|
// which mean we have to manually mark the ctors.
|
|
for (const ObjFile *Obj : Symtab->ObjectFiles) {
|
|
const WasmLinkingData &L = Obj->getWasmObj()->linkingData();
|
|
for (const WasmInitFunc &F : L.InitFunctions)
|
|
Enqueue(Obj->getFunctionSymbol(F.FunctionIndex));
|
|
}
|
|
|
|
auto EnqueueSuccessors = [Enqueue](InputChunk &Chunk) {
|
|
for (const WasmRelocation Reloc : Chunk.getRelocations()) {
|
|
switch (Reloc.Type) {
|
|
case R_WEBASSEMBLY_FUNCTION_INDEX_LEB:
|
|
case R_WEBASSEMBLY_TABLE_INDEX_I32:
|
|
case R_WEBASSEMBLY_TABLE_INDEX_SLEB:
|
|
Enqueue(Chunk.File->getFunctionSymbol(Reloc.Index));
|
|
break;
|
|
case R_WEBASSEMBLY_GLOBAL_INDEX_LEB:
|
|
case R_WEBASSEMBLY_MEMORY_ADDR_LEB:
|
|
case R_WEBASSEMBLY_MEMORY_ADDR_SLEB:
|
|
case R_WEBASSEMBLY_MEMORY_ADDR_I32:
|
|
Enqueue(Chunk.File->getGlobalSymbol(Reloc.Index));
|
|
break;
|
|
}
|
|
}
|
|
};
|
|
|
|
while (!Q.empty())
|
|
EnqueueSuccessors(*Q.pop_back_val());
|
|
|
|
// Report garbage-collected sections.
|
|
if (Config->PrintGcSections) {
|
|
auto CheckChunk = [](const InputChunk *C) {
|
|
if (!C->Live)
|
|
message("removing unused section '" + C->getName() + "' in file '" +
|
|
C->getFileName() + "'");
|
|
};
|
|
|
|
for (const ObjFile *Obj : Symtab->ObjectFiles) {
|
|
for (InputChunk *C : Obj->Functions)
|
|
CheckChunk(C);
|
|
for (InputChunk *C : Obj->Segments)
|
|
CheckChunk(C);
|
|
}
|
|
}
|
|
}
|