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/*
* Copyright 2016 WebAssembly Community Group participants
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
// (very) basic linking functionality for s2wasm.
// Performs some of the tasks that will eventually be done by a real linker.
// Currently can allocate static variables and the stack, lay out memory
// and initial segment contents, and process relocations. (In particular, there
// is no merging of multiple modules). Currently this is only inteded to turn
// a .s file produced by LLVM into a usable wast file.
#ifndef WASM_WASM_LINK_H
#define WASM_WASM_LINK_H
#include "support/utilities.h"
#include "wasm.h"
namespace wasm {
class Linker {
public:
struct Relocation {
enum Kind { kData, kFunction };
Kind kind; // Whether the symbol refers to data or a function.
// Instead of section offsets as relocation targets, for now this is just
// a pointer to the memory to rewrite.
uint32_t* data;
Name symbol; // Like the symbol index in ELF r_info field
int addend; // Like the ELF r_addend field
Relocation(Kind kind, uint32_t* data, Name symbol, int addend) :
kind(kind), data(data), symbol(symbol), addend(addend) {}
};
Linker(Module& wasm, size_t globalBase, size_t stackAllocation,
size_t userInitialMemory, size_t userMaxMemory,
bool ignoreUnknownSymbols, Name startFunction,
bool debug) :
wasm(wasm),
ignoreUnknownSymbols(ignoreUnknownSymbols),
startFunction(startFunction),
globalBase(globalBase),
nextStatic(globalBase),
userInitialMemory(userInitialMemory),
userMaxMemory(userMaxMemory),
stackAllocation(stackAllocation),
debug(debug) {
if (userMaxMemory && userMaxMemory < userInitialMemory) {
Fatal() << "Specified max memory " << userMaxMemory <<
" is < specified initial memory " << userInitialMemory;
}
if (roundUpToPageSize(userMaxMemory) != userMaxMemory) {
Fatal() << "Specified max memory " << userMaxMemory <<
" is not a multiple of 64k";
}
if (roundUpToPageSize(userInitialMemory) != userInitialMemory) {
Fatal() << "Specified initial memory " << userInitialMemory <<
" is not a multiple of 64k";
}
// Don't allow anything to be allocated at address 0
if (globalBase == 0) nextStatic = 1;
// Place the stack pointer at the bottom of the linear memory, to keep its
// address small (and thus with a small encoding).
placeStackPointer(stackAllocation);
// Allocate __dso_handle. For asm.js, emscripten provides this in JS, but
// wasm modules can't import data objects. Its value is 0 for the main
// executable, which is all we have with static linking. In the future this
// can go in a crtbegin or similar file.
addStatic(4, 4, "__dso_handle");
}
// Allocate a static variable and return its address in linear memory
size_t allocateStatic(size_t allocSize, size_t alignment, Name name) {
size_t address = alignAddr(nextStatic, alignment);
staticAddresses[name] = address;
nextStatic = address + allocSize;
return address;
}
// Allocate a static object
void addStatic(size_t allocSize, size_t alignment, Name name) {
staticObjects.emplace_back(allocSize, alignment, name);
}
void addGlobal(Name name) {
globls.push_back(name);
}
void addRelocation(Relocation::Kind kind, uint32_t* target, Name name, int addend) {
relocations.emplace_back(make_unique<Relocation>(kind, target, name, addend));
}
Relocation* getCurrentRelocation() {
return relocations.back().get();
}
void addImplementedFunction(Name name) {
implementedFunctions.insert(name);
}
bool isFunctionImplemented(Name name) {
return implementedFunctions.count(name) != 0;
}
void addAliasedFunction(Name name, Name alias) {
aliasedFunctions.insert({name, alias});
}
// If name is an alias, return what it points to. Otherwise return name
Name resolveAlias(Name name) {
auto aliased = aliasedFunctions.find(name);
if (aliased != aliasedFunctions.end()) return aliased->second;
return name;
}
// Add an initializer segment for the named static variable.
void addSegment(Name name, const char* data, size_t size) {
segments[name] = wasm.memory.segments.size();
wasm.memory.segments.emplace_back(0, data, size);
}
void addInitializerFunction(Name name) {
initializerFunctions.emplace_back(name);
assert(implementedFunctions.count(name));
}
// Allocate the user stack, set up the initial memory size of the module, lay
// out the linear memory, process the relocations, and set up the indirect
// function table.
void layout();
// Support for emscripten integration: generates dyncall thunks, emits
// metadata for asmConsts, staticBump and initializer functions.
void emscriptenGlue(std::ostream& o);
private:
struct StaticObject {
size_t allocSize;
size_t alignment;
Name name;
StaticObject(size_t allocSize, size_t alignment, Name name) :
allocSize(allocSize), alignment(alignment), name(name) {}
};
// Allocate space for a stack pointer and (if stackAllocation > 0) set up a
// relocation for it to point to the top of the stack.
void placeStackPointer(size_t stackAllocation);
template<class C>
void printSet(std::ostream& o, C& c) {
o << "[";
bool first = true;
for (auto& item : c) {
if (first) first = false;
else o << ",";
o << '"' << item << '"';
}
o << "]";
}
// Create thunks for use with emscripten Runtime.dynCall. Creates one for each
// signature in the indirect function table.
void makeDynCallThunks();
static size_t roundUpToPageSize(size_t size) {
return (size + Memory::kPageSize - 1) & Memory::kPageMask;
}
void exportFunction(Name name, bool must_export) {
if (!wasm.checkFunction(name)) {
assert(!must_export);
return;
}
if (wasm.checkExport(name)) return; // Already exported
auto exp = wasm.allocator.alloc<Export>();
exp->name = exp->value = name;
wasm.addExport(exp);
}
Module& wasm;
bool ignoreUnknownSymbols;
Name startFunction;
std::vector<Name> globls;
// where globals can start to be statically allocated, i.e., the data segment
size_t globalBase;
size_t nextStatic; // location of next static allocation
size_t userInitialMemory; // Initial memory size (in bytes) specified by the user.
size_t userMaxMemory; // Max memory size (in bytes) specified by the user.
//(after linking, this is rounded and set on the wasm object in pages)
size_t stackAllocation;
bool debug;
std::vector<StaticObject> staticObjects;
std::unordered_map<cashew::IString, int32_t> staticAddresses; // name => address
std::vector<std::unique_ptr<Relocation>> relocations;
std::set<Name> implementedFunctions;
std::unordered_map<cashew::IString, Name> aliasedFunctions;
std::map<Name, size_t> segments; // name => segment index (in wasm module)
std::unordered_map<size_t, size_t> segmentsByAddress; // address => segment index
std::unordered_map<cashew::IString, size_t> functionIndexes;
std::vector<Name> initializerFunctions;
};
}
#endif // WASM_WASM_LINK_H
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