Commit f8d1efd99a
src/link/Wasm.zig
@@ -118,6 +118,9 @@ memories: std.wasm.Memory = .{ .limits = .{ .min = 0, .max = null } },
tables: std.ArrayListUnmanaged(std.wasm.Table) = .{},
/// Output export section
exports: std.ArrayListUnmanaged(types.Export) = .{},
+/// List of initialization functions. These must be called in order of priority
+/// by the (synthetic) __wasm_call_ctors function.
+init_funcs: std.ArrayListUnmanaged(InitFuncLoc) = .{},
/// Indirect function table, used to call function pointers
/// When this is non-zero, we must emit a table entry,
@@ -238,6 +241,34 @@ pub const SymbolLoc = struct {
}
};
+// Contains the location of the function symbol, as well as
+/// the priority itself of the initialization function.
+pub const InitFuncLoc = struct {
+ /// object file index in the list of objects.
+ /// Unlike `SymbolLoc` this cannot be `null` as we never define
+ /// our own ctors.
+ file: u16,
+ /// Symbol index within the corresponding object file.
+ index: u32,
+ /// The priority in which the constructor must be called.
+ priority: u32,
+
+ /// From a given `InitFuncLoc` returns the corresponding function symbol
+ fn getSymbol(loc: InitFuncLoc, wasm: *const Wasm) *Symbol {
+ return getSymbolLoc(loc).getSymbol(wasm);
+ }
+
+ /// Turns the given `InitFuncLoc` into a `SymbolLoc`
+ fn getSymbolLoc(loc: InitFuncLoc) SymbolLoc {
+ return .{ .file = loc.file, .index = loc.index };
+ }
+
+ /// Returns true when `lhs` has a higher priority (e.i. value closer to 0) than `rhs`.
+ fn lessThan(ctx: void, lhs: InitFuncLoc, rhs: InitFuncLoc) bool {
+ _ = ctx;
+ return lhs.priority < rhs.priority;
+ }
+};
/// Generic string table that duplicates strings
/// and converts them into offsets instead.
pub const StringTable = struct {
@@ -393,6 +424,16 @@ pub fn openPath(allocator: Allocator, sub_path: []const u8, options: link.Option
}
}
+ // create __wasm_call_ctors
+ {
+ const loc = try wasm_bin.createSyntheticSymbol("__wasm_call_ctors", .function);
+ const symbol = loc.getSymbol(wasm_bin);
+ symbol.setFlag(.WASM_SYM_VISIBILITY_HIDDEN);
+ // we do not know the function index until after we merged all sections.
+ // Therefore we set `symbol.index` and create its corresponding references
+ // at the end during `initializeCallCtorsFunction`.
+ }
+
if (!options.strip and options.module != null) {
wasm_bin.dwarf = Dwarf.init(allocator, &wasm_bin.base, options.target);
try wasm_bin.initDebugSections();
@@ -896,6 +937,7 @@ pub fn deinit(wasm: *Wasm) void {
wasm.wasm_globals.deinit(gpa);
wasm.function_table.deinit(gpa);
wasm.tables.deinit(gpa);
+ wasm.init_funcs.deinit(gpa);
wasm.exports.deinit(gpa);
wasm.string_table.deinit(gpa);
@@ -1698,6 +1740,130 @@ fn sortDataSegments(wasm: *Wasm) !void {
wasm.data_segments = new_mapping;
}
+/// Obtains all initfuncs from each object file, verifies its function signature,
+/// and then appends it to our final `init_funcs` list.
+/// After all functions have been inserted, the functions will be ordered based
+/// on their priority.
+/// NOTE: This function must be called before we merged any other section.
+/// This is because all init funcs in the object files contain references to the
+/// original functions and their types. We need to know the type to verify it doesn't
+/// contain any parameters.
+fn setupInitFunctions(wasm: *Wasm) !void {
+ for (wasm.objects.items) |object, file_index| {
+ try wasm.init_funcs.ensureUnusedCapacity(wasm.base.allocator, object.init_funcs.len);
+ for (object.init_funcs) |init_func| {
+ const symbol = object.symtable[init_func.symbol_index];
+ const ty: std.wasm.Type = if (symbol.isUndefined()) ty: {
+ const imp: types.Import = object.findImport(.function, symbol.index);
+ break :ty object.func_types[imp.kind.function];
+ } else ty: {
+ const func_index = symbol.index - object.importedCountByKind(.function);
+ const func = object.functions[func_index];
+ break :ty object.func_types[func.type_index];
+ };
+ if (ty.params.len != 0) {
+ log.err("constructor functions cannot take arguments: '{s}'", .{object.string_table.get(symbol.name)});
+ return error.InvalidInitFunc;
+ }
+ log.debug("appended init func '{s}'\n", .{object.string_table.get(symbol.name)});
+ wasm.init_funcs.appendAssumeCapacity(.{
+ .index = init_func.symbol_index,
+ .file = @intCast(u16, file_index),
+ .priority = init_func.priority,
+ });
+ }
+ }
+
+ // sort the initfunctions based on their priority
+ std.sort.sort(InitFuncLoc, wasm.init_funcs.items, {}, InitFuncLoc.lessThan);
+}
+
+/// Creates a function body for the `__wasm_call_ctors` symbol.
+/// Loops over all constructors found in `init_funcs` and calls them
+/// respectively based on their priority which was sorted by `setupInitFunctions`.
+/// NOTE: This function must be called after we merged all sections to ensure the
+/// references to the function stored in the symbol have been finalized so we end
+/// up calling the resolved function.
+fn initializeCallCtorsFunction(wasm: *Wasm) !void {
+ // No code to emit, so also no ctors to call
+ if (wasm.code_section_index == null) {
+ // Make sure to remove it from the resolved symbols so we do not emit
+ // it within any section. TODO: Remove this once we implement garbage collection.
+ const loc = wasm.globals.get(wasm.string_table.getOffset("__wasm_call_ctors").?).?;
+ std.debug.assert(wasm.resolved_symbols.swapRemove(loc));
+ return;
+ }
+
+ var function_body = std.ArrayList(u8).init(wasm.base.allocator);
+ defer function_body.deinit();
+ const writer = function_body.writer();
+
+ // Create the function body
+ {
+ // Write locals count (we have none)
+ try leb.writeULEB128(writer, @as(u32, 0));
+
+ // call constructors
+ for (wasm.init_funcs.items) |init_func_loc| {
+ const symbol = init_func_loc.getSymbol(wasm);
+ if (symbol.isUndefined()) {
+ std.debug.print("Undefined symbol '{s}'\n", .{wasm.string_table.get(symbol.name)});
+ }
+ std.debug.print("Symbol: {s}\n", .{init_func_loc.getSymbolLoc().getName(wasm)});
+ std.debug.assert(wasm.resolved_symbols.contains(init_func_loc.getSymbolLoc().finalLoc(wasm)));
+ const func = wasm.functions.values()[symbol.index - wasm.imported_functions_count];
+ const ty = wasm.func_types.items[func.type_index];
+
+ // Call function by its function index
+ try writer.writeByte(std.wasm.opcode(.call));
+ try leb.writeULEB128(writer, symbol.index);
+
+ // drop all returned values from the stack as __wasm_call_ctors has no return value
+ for (ty.returns) |_| {
+ try writer.writeByte(std.wasm.opcode(.drop));
+ }
+ }
+
+ // End function body
+ try writer.writeByte(std.wasm.opcode(.end));
+ }
+
+ const loc = wasm.globals.get(wasm.string_table.getOffset("__wasm_call_ctors").?).?;
+ const symbol = loc.getSymbol(wasm);
+ // create type (() -> nil) as we do not have any parameters or return value.
+ const ty_index = try wasm.putOrGetFuncType(.{ .params = &[_]std.wasm.Valtype{}, .returns = &[_]std.wasm.Valtype{} });
+ // create function with above type
+ const func_index = wasm.imported_functions_count + @intCast(u32, wasm.functions.count());
+ try wasm.functions.putNoClobber(
+ wasm.base.allocator,
+ .{ .file = null, .index = func_index },
+ .{ .type_index = ty_index },
+ );
+ symbol.index = func_index;
+
+ // create the atom that will be output into the final binary
+ const atom = try wasm.base.allocator.create(Atom);
+ errdefer wasm.base.allocator.destroy(atom);
+ atom.* = .{
+ .size = @intCast(u32, function_body.items.len),
+ .offset = 0,
+ .sym_index = loc.index,
+ .file = null,
+ .alignment = 1,
+ .next = null,
+ .prev = null,
+ .code = function_body.moveToUnmanaged(),
+ .dbg_info_atom = undefined,
+ };
+ try wasm.managed_atoms.append(wasm.base.allocator, atom);
+ try wasm.appendAtomAtIndex(wasm.code_section_index.?, atom);
+ try wasm.symbol_atom.putNoClobber(wasm.base.allocator, loc, atom);
+
+ // `allocateAtoms` has already been called, set the atom's offset manually.
+ // This is fine to do manually as we insert the atom at the very end.
+ atom.offset = atom.prev.?.offset + atom.prev.?.size;
+}
+
fn setupImports(wasm: *Wasm) !void {
log.debug("Merging imports", .{});
var discarded_it = wasm.discarded.keyIterator();
@@ -1870,16 +2036,17 @@ fn setupExports(wasm: *Wasm) !void {
const force_exp_names = wasm.base.options.export_symbol_names;
if (force_exp_names.len > 0) {
- var failed_exports = try std.ArrayList([]const u8).initCapacity(wasm.base.allocator, force_exp_names.len);
- defer failed_exports.deinit();
+ var failed_exports = false;
for (force_exp_names) |exp_name| {
const name_index = wasm.string_table.getOffset(exp_name) orelse {
- failed_exports.appendAssumeCapacity(exp_name);
+ log.err("could not export '{s}', symbol not found", .{exp_name});
+ failed_exports = true;
continue;
};
const loc = wasm.globals.get(name_index) orelse {
- failed_exports.appendAssumeCapacity(exp_name);
+ log.err("could not export '{s}', symbol not found", .{exp_name});
+ failed_exports = true;
continue;
};
@@ -1887,10 +2054,7 @@ fn setupExports(wasm: *Wasm) !void {
symbol.setFlag(.WASM_SYM_EXPORTED);
}
- if (failed_exports.items.len > 0) {
- for (failed_exports.items) |exp_name| {
- log.err("could not export '{s}', symbol not found", .{exp_name});
- }
+ if (failed_exports) {
return error.MissingSymbol;
}
}
@@ -1948,6 +2112,7 @@ fn setupStart(wasm: *Wasm) !void {
const symbol_loc = wasm.globals.get(symbol_name_offset) orelse {
log.err("Entry symbol '{s}' not found", .{entry_name});
+ return error.MissingSymbol;
};
const symbol = symbol_loc.getSymbol(wasm);
if (symbol.tag != .function) {
@@ -2503,6 +2668,7 @@ fn linkWithZld(wasm: *Wasm, comp: *Compilation, prog_node: *std.Progress.Node) l
try wasm.resolveSymbolsInArchives();
try wasm.checkUndefinedSymbols();
+ try wasm.setupInitFunctions();
try wasm.setupStart();
try wasm.setupImports();
@@ -2515,6 +2681,7 @@ fn linkWithZld(wasm: *Wasm, comp: *Compilation, prog_node: *std.Progress.Node) l
wasm.mapFunctionTable();
try wasm.mergeSections();
try wasm.mergeTypes();
+ try wasm.initializeCallCtorsFunction();
try wasm.setupExports();
try wasm.writeToFile(enabled_features, emit_features_count, arena);
@@ -2587,6 +2754,7 @@ pub fn flushModule(wasm: *Wasm, comp: *Compilation, prog_node: *std.Progress.Nod
// When we finish/error we reset the state of the linker
// So we can rebuild the binary file on each incremental update
defer wasm.resetState();
+ try wasm.setupInitFunctions();
try wasm.setupStart();
try wasm.setupImports();
if (wasm.base.options.module) |mod| {
@@ -2629,6 +2797,7 @@ pub fn flushModule(wasm: *Wasm, comp: *Compilation, prog_node: *std.Progress.Nod
wasm.mapFunctionTable();
try wasm.mergeSections();
try wasm.mergeTypes();
+ try wasm.initializeCallCtorsFunction();
try wasm.setupExports();
try wasm.writeToFile(enabled_features, emit_features_count, arena);
}
@@ -3909,8 +4078,8 @@ pub fn getTypeIndex(wasm: *const Wasm, func_type: std.wasm.Type) ?u32 {
return null;
}
-/// Searches for an a matching function signature, when not found
-/// a new entry will be made. The index of the existing/new signature will be returned.
+/// Searches for a matching function signature. When no matching signature is found,
+/// a new entry will be made. The value returned is the index of the type within `wasm.func_types`.
pub fn putOrGetFuncType(wasm: *Wasm, func_type: std.wasm.Type) !u32 {
if (wasm.getTypeIndex(func_type)) |index| {
return index;
src/link.zig
@@ -716,6 +716,7 @@ pub const File = struct {
InvalidFeatureSet,
InvalidFormat,
InvalidIndex,
+ InvalidInitFunc,
InvalidMagicByte,
InvalidWasmVersion,
LLDCrashed,