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| 1 | const Wasm = @This(); |
| 2 | |
| 3 | const std = @import("std"); |
| 4 | const Allocator = std.mem.Allocator; |
| 5 | const assert = std.debug.assert; |
| 6 | const fs = std.fs; |
| 7 | const leb = std.debug.leb; |
| 8 | |
| 9 | const Module = @import("../Module.zig"); |
| 10 | const codegen = @import("../codegen/wasm.zig"); |
| 11 | const link = @import("../link.zig"); |
| 12 | |
| 13 | /// Various magic numbers defined by the wasm spec |
| 14 | const spec = struct { |
| 15 | const magic = [_]u8{ 0x00, 0x61, 0x73, 0x6D }; // \0asm |
| 16 | const version = [_]u8{ 0x01, 0x00, 0x00, 0x00 }; // version 1 |
| 17 | |
| 18 | const custom_id = 0; |
| 19 | const types_id = 1; |
| 20 | const imports_id = 2; |
| 21 | const funcs_id = 3; |
| 22 | const tables_id = 4; |
| 23 | const memories_id = 5; |
| 24 | const globals_id = 6; |
| 25 | const exports_id = 7; |
| 26 | const start_id = 8; |
| 27 | const elements_id = 9; |
| 28 | const code_id = 10; |
| 29 | const data_id = 11; |
| 30 | }; |
| 31 | |
| 32 | pub const base_tag = link.File.Tag.wasm; |
| 33 | |
| 34 | pub const FnData = struct { |
| 35 | funcidx: u32, |
| 36 | typeidx: u32, |
| 37 | }; |
| 38 | |
| 39 | base: link.File, |
| 40 | |
| 41 | types: Types, |
| 42 | funcs: Funcs, |
| 43 | exports: Exports, |
| 44 | |
| 45 | /// Array over the section structs used in the various sections above to |
| 46 | /// allow iteration when shifting sections to make space. |
| 47 | /// TODO: this should eventually be size 11 when we use all the sections. |
| 48 | sections: [4]*Section, |
| 49 | |
| 50 | pub fn openPath(allocator: *Allocator, dir: fs.Dir, sub_path: []const u8, options: link.Options) !*link.File { |
| 51 | assert(options.object_format == .wasm); |
| 52 | |
| 53 | // TODO: read the file and keep vaild parts instead of truncating |
| 54 | const file = try dir.createFile(sub_path, .{ .truncate = true, .read = true }); |
| 55 | errdefer file.close(); |
| 56 | |
| 57 | const wasm = try allocator.create(Wasm); |
| 58 | errdefer allocator.destroy(wasm); |
| 59 | |
| 60 | try file.writeAll(&(spec.magic ++ spec.version)); |
| 61 | |
| 62 | wasm.base = .{ |
| 63 | .tag = .wasm, |
| 64 | .options = options, |
| 65 | .file = file, |
| 66 | .allocator = allocator, |
| 67 | }; |
| 68 | |
| 69 | // TODO: this should vary depending on the section and be less arbitrary |
| 70 | const size = 1024; |
| 71 | const offset = @sizeOf(@TypeOf(spec.magic ++ spec.version)); |
| 72 | |
| 73 | wasm.types = try Types.init(file, offset, size); |
| 74 | wasm.funcs = try Funcs.init(file, offset + size, size, offset + 3 * size, size); |
| 75 | wasm.exports = try Exports.init(file, offset + 2 * size, size); |
| 76 | try file.setEndPos(offset + 4 * size); |
| 77 | |
| 78 | wasm.sections = [_]*Section{ |
| 79 | &wasm.types.typesec.section, |
| 80 | &wasm.funcs.funcsec, |
| 81 | &wasm.exports.exportsec, |
| 82 | &wasm.funcs.codesec.section, |
| 83 | }; |
| 84 | |
| 85 | return &wasm.base; |
| 86 | } |
| 87 | |
| 88 | pub fn deinit(self: *Wasm) void { |
| 89 | if (self.base.file) |f| f.close(); |
| 90 | self.types.deinit(); |
| 91 | self.funcs.deinit(); |
| 92 | } |
| 93 | |
| 94 | pub fn updateDecl(self: *Wasm, module: *Module, decl: *Module.Decl) !void { |
| 95 | if (decl.typed_value.most_recent.typed_value.ty.zigTypeTag() != .Fn) |
| 96 | return error.TODOImplementNonFnDeclsForWasm; |
| 97 | |
| 98 | if (decl.fn_link.wasm) |fn_data| { |
| 99 | self.types.free(fn_data.typeidx); |
| 100 | self.funcs.free(fn_data.funcidx); |
| 101 | } |
| 102 | |
| 103 | var buf = std.ArrayList(u8).init(self.base.allocator); |
| 104 | defer buf.deinit(); |
| 105 | |
| 106 | try codegen.genFunctype(&buf, decl); |
| 107 | const typeidx = try self.types.new(buf.items); |
| 108 | buf.items.len = 0; |
| 109 | |
| 110 | try codegen.genCode(&buf, decl); |
| 111 | const funcidx = try self.funcs.new(typeidx, buf.items); |
| 112 | |
| 113 | decl.fn_link.wasm = .{ .typeidx = typeidx, .funcidx = funcidx }; |
| 114 | |
| 115 | try self.exports.writeAll(module); |
| 116 | } |
| 117 | |
| 118 | pub fn updateDeclExports( |
| 119 | self: *Wasm, |
| 120 | module: *Module, |
| 121 | decl: *const Module.Decl, |
| 122 | exports: []const *Module.Export, |
| 123 | ) !void { |
| 124 | // TODO: updateDeclExports() may currently be called before updateDecl, |
| 125 | // presumably due to a bug. For now just rely on the following call |
| 126 | // being made in updateDecl(). |
| 127 | |
| 128 | //try self.exports.writeAll(module); |
| 129 | } |
| 130 | |
| 131 | pub fn freeDecl(self: *Wasm, decl: *Module.Decl) void { |
| 132 | // TODO: remove this assert when non-function Decls are implemented |
| 133 | assert(decl.typed_value.most_recent.typed_value.ty.zigTypeTag() == .Fn); |
| 134 | if (decl.fn_link.wasm) |fn_data| { |
| 135 | self.types.free(fn_data.typeidx); |
| 136 | self.funcs.free(fn_data.funcidx); |
| 137 | decl.fn_link.wasm = null; |
| 138 | } |
| 139 | } |
| 140 | |
| 141 | pub fn flush(self: *Wasm) !void {} |
| 142 | |
| 143 | /// This struct describes the location of a named section + custom section |
| 144 | /// padding in the output file. This is all the data we need to allow for |
| 145 | /// shifting sections around when padding runs out. |
| 146 | const Section = struct { |
| 147 | /// The size of a section header: 1 byte section id + 5 bytes |
| 148 | /// for the fixed-width ULEB128 encoded contents size. |
| 149 | const header_size = 1 + 5; |
| 150 | /// Offset of the section id byte from the start of the file. |
| 151 | offset: u64, |
| 152 | /// Size of the section, including the header and directly |
| 153 | /// following custom section used for padding if any. |
| 154 | size: u64, |
| 155 | |
| 156 | /// Resize the usable part of the section, handling the following custom |
| 157 | /// section used for padding. If there is not enough padding left, shift |
| 158 | /// all following sections to make space. Takes the current and target |
| 159 | /// contents sizes of the section as arguments. |
| 160 | fn resize(self: *Section, file: fs.File, current: u32, target: u32) !void { |
| 161 | // Section header + target contents size + custom section header |
| 162 | // + custom section name + empty custom section > owned chunk of the file |
| 163 | if (header_size + target + header_size + 1 + 0 > self.size) |
| 164 | return error.TODOImplementSectionShifting; |
| 165 | |
| 166 | const new_custom_start = self.offset + header_size + target; |
| 167 | const new_custom_contents_size = self.size - target - 2 * header_size; |
| 168 | assert(new_custom_contents_size >= 1); |
| 169 | // +1 for the name of the custom section, which we set to an empty string |
| 170 | var custom_header: [header_size + 1]u8 = undefined; |
| 171 | custom_header[0] = spec.custom_id; |
| 172 | leb.writeUnsignedFixed(5, custom_header[1..header_size], @intCast(u32, new_custom_contents_size)); |
| 173 | custom_header[header_size] = 0; |
| 174 | try file.pwriteAll(&custom_header, new_custom_start); |
| 175 | } |
| 176 | }; |
| 177 | |
| 178 | /// This can be used to manage the contents of any section which uses a vector |
| 179 | /// of contents. This interface maintains index stability while allowing for |
| 180 | /// reuse of "dead" indexes. |
| 181 | const VecSection = struct { |
| 182 | /// Represents a single entry in the vector (e.g. a type in the type section) |
| 183 | const Entry = struct { |
| 184 | /// Offset from the start of the section contents in bytes |
| 185 | offset: u32, |
| 186 | /// Size in bytes of the entry |
| 187 | size: u32, |
| 188 | }; |
| 189 | section: Section, |
| 190 | /// Size in bytes of the contents of the section. Does not include |
| 191 | /// the "header" containing the section id and this value. |
| 192 | contents_size: u32, |
| 193 | /// List of all entries in the contents of the section. |
| 194 | entries: std.ArrayListUnmanaged(Entry) = std.ArrayListUnmanaged(Entry){}, |
| 195 | /// List of indexes of unreferenced entries which may be |
| 196 | /// overwritten and reused. |
| 197 | dead_list: std.ArrayListUnmanaged(u32) = std.ArrayListUnmanaged(u32){}, |
| 198 | |
| 199 | /// Write the headers of the section and custom padding section |
| 200 | fn init(comptime section_id: u8, file: fs.File, offset: u64, initial_size: u64) !VecSection { |
| 201 | // section id, section size, empty vector, custom section id, |
| 202 | // custom section size, empty custom section name |
| 203 | var initial_data: [1 + 5 + 5 + 1 + 5 + 1]u8 = undefined; |
| 204 | |
| 205 | assert(initial_size >= initial_data.len); |
| 206 | |
| 207 | comptime var i = 0; |
| 208 | initial_data[i] = section_id; |
| 209 | i += 1; |
| 210 | leb.writeUnsignedFixed(5, initial_data[i..(i + 5)], 5); |
| 211 | i += 5; |
| 212 | leb.writeUnsignedFixed(5, initial_data[i..(i + 5)], 0); |
| 213 | i += 5; |
| 214 | initial_data[i] = spec.custom_id; |
| 215 | i += 1; |
| 216 | leb.writeUnsignedFixed(5, initial_data[i..(i + 5)], @intCast(u32, initial_size - @sizeOf(@TypeOf(initial_data)))); |
| 217 | i += 5; |
| 218 | initial_data[i] = 0; |
| 219 | |
| 220 | try file.pwriteAll(&initial_data, offset); |
| 221 | |
| 222 | return VecSection{ |
| 223 | .section = .{ |
| 224 | .offset = offset, |
| 225 | .size = initial_size, |
| 226 | }, |
| 227 | .contents_size = 5, |
| 228 | }; |
| 229 | } |
| 230 | |
| 231 | fn deinit(self: *VecSection, allocator: *Allocator) void { |
| 232 | self.entries.deinit(allocator); |
| 233 | self.dead_list.deinit(allocator); |
| 234 | } |
| 235 | |
| 236 | /// Write a new entry into the file, returning the index used. |
| 237 | fn addEntry(self: *VecSection, file: fs.File, allocator: *Allocator, data: []const u8) !u32 { |
| 238 | // First look for a dead entry we can reuse |
| 239 | for (self.dead_list.items) |dead_idx, i| { |
| 240 | const dead_entry = &self.entries.items[dead_idx]; |
| 241 | if (dead_entry.size == data.len) { |
| 242 | // Found a dead entry of the right length, overwrite it |
| 243 | try file.pwriteAll(data, self.section.offset + Section.header_size + dead_entry.offset); |
| 244 | _ = self.dead_list.swapRemove(i); |
| 245 | return dead_idx; |
| 246 | } |
| 247 | } |
| 248 | |
| 249 | // TODO: We can be more efficient if we special-case one or |
| 250 | // more consecutive dead entries at the end of the vector. |
| 251 | |
| 252 | // We failed to find a dead entry to reuse, so write the new |
| 253 | // entry to the end of the section. |
| 254 | try self.section.resize(file, self.contents_size, self.contents_size + @intCast(u32, data.len)); |
| 255 | try file.pwriteAll(data, self.section.offset + Section.header_size + self.contents_size); |
| 256 | try self.entries.append(allocator, .{ |
| 257 | .offset = self.contents_size, |
| 258 | .size = @intCast(u32, data.len), |
| 259 | }); |
| 260 | self.contents_size += @intCast(u32, data.len); |
| 261 | // Make sure the dead list always has enough space to store all free'd |
| 262 | // entries. This makes it so that delEntry() cannot fail. |
| 263 | // TODO: figure out a better way that doesn't waste as much memory |
| 264 | try self.dead_list.ensureCapacity(allocator, self.entries.items.len); |
| 265 | |
| 266 | // Update the size in the section header and the item count of |
| 267 | // the contents vector. |
| 268 | var size_and_count: [10]u8 = undefined; |
| 269 | leb.writeUnsignedFixed(5, size_and_count[0..5], self.contents_size); |
| 270 | leb.writeUnsignedFixed(5, size_and_count[5..], @intCast(u32, self.entries.items.len)); |
| 271 | try file.pwriteAll(&size_and_count, self.section.offset + 1); |
| 272 | |
| 273 | return @intCast(u32, self.entries.items.len - 1); |
| 274 | } |
| 275 | |
| 276 | /// Mark the type referenced by the given index as dead. |
| 277 | fn delEntry(self: *VecSection, index: u32) void { |
| 278 | self.dead_list.appendAssumeCapacity(index); |
| 279 | } |
| 280 | }; |
| 281 | |
| 282 | const Types = struct { |
| 283 | typesec: VecSection, |
| 284 | |
| 285 | fn init(file: fs.File, offset: u64, initial_size: u64) !Types { |
| 286 | return Types{ .typesec = try VecSection.init(spec.types_id, file, offset, initial_size) }; |
| 287 | } |
| 288 | |
| 289 | fn deinit(self: *Types) void { |
| 290 | const wasm = @fieldParentPtr(Wasm, "types", self); |
| 291 | self.typesec.deinit(wasm.base.allocator); |
| 292 | } |
| 293 | |
| 294 | fn new(self: *Types, data: []const u8) !u32 { |
| 295 | const wasm = @fieldParentPtr(Wasm, "types", self); |
| 296 | return self.typesec.addEntry(wasm.base.file.?, wasm.base.allocator, data); |
| 297 | } |
| 298 | |
| 299 | fn free(self: *Types, typeidx: u32) void { |
| 300 | self.typesec.delEntry(typeidx); |
| 301 | } |
| 302 | }; |
| 303 | |
| 304 | const Funcs = struct { |
| 305 | /// This section needs special handling to keep the indexes matching with |
| 306 | /// the codesec, so we cant just use a VecSection. |
| 307 | funcsec: Section, |
| 308 | /// Number of functions listed in the funcsec. Must be kept in sync with |
| 309 | /// codesec.entries.items.len. |
| 310 | funcs_count: u32, |
| 311 | codesec: VecSection, |
| 312 | |
| 313 | fn init(file: fs.File, funcs_offset: u64, funcs_size: u64, code_offset: u64, code_size: u64) !Funcs { |
| 314 | return Funcs{ |
| 315 | .funcsec = (try VecSection.init(spec.funcs_id, file, funcs_offset, funcs_size)).section, |
| 316 | .funcs_count = 0, |
| 317 | .codesec = try VecSection.init(spec.code_id, file, code_offset, code_size), |
| 318 | }; |
| 319 | } |
| 320 | |
| 321 | fn deinit(self: *Funcs) void { |
| 322 | const wasm = @fieldParentPtr(Wasm, "funcs", self); |
| 323 | self.codesec.deinit(wasm.base.allocator); |
| 324 | } |
| 325 | |
| 326 | /// Add a new function to the binary, first finding space for and writing |
| 327 | /// the code then writing the typeidx to the corresponding index in the |
| 328 | /// funcsec. Returns the function index used. |
| 329 | fn new(self: *Funcs, typeidx: u32, code: []const u8) !u32 { |
| 330 | const wasm = @fieldParentPtr(Wasm, "funcs", self); |
| 331 | const file = wasm.base.file.?; |
| 332 | const allocator = wasm.base.allocator; |
| 333 | |
| 334 | assert(self.funcs_count == self.codesec.entries.items.len); |
| 335 | |
| 336 | // TODO: consider nop-padding the code if there is a close but not perfect fit |
| 337 | const funcidx = try self.codesec.addEntry(file, allocator, code); |
| 338 | |
| 339 | if (self.funcs_count < self.codesec.entries.items.len) { |
| 340 | // u32 vector length + funcs_count u32s in the vector |
| 341 | const current = 5 + self.funcs_count * 5; |
| 342 | try self.funcsec.resize(file, current, current + 5); |
| 343 | self.funcs_count += 1; |
| 344 | |
| 345 | // Update the size in the section header and the item count of |
| 346 | // the contents vector. |
| 347 | var size_and_count: [10]u8 = undefined; |
| 348 | leb.writeUnsignedFixed(5, size_and_count[0..5], 5 + self.funcs_count * 5); |
| 349 | leb.writeUnsignedFixed(5, size_and_count[5..], self.funcs_count); |
| 350 | try file.pwriteAll(&size_and_count, self.funcsec.offset + 1); |
| 351 | } |
| 352 | assert(self.funcs_count == self.codesec.entries.items.len); |
| 353 | |
| 354 | var typeidx_leb: [5]u8 = undefined; |
| 355 | leb.writeUnsignedFixed(5, &typeidx_leb, typeidx); |
| 356 | try file.pwriteAll(&typeidx_leb, self.funcsec.offset + Section.header_size + 5 + funcidx * 5); |
| 357 | |
| 358 | return funcidx; |
| 359 | } |
| 360 | |
| 361 | fn free(self: *Funcs, funcidx: u32) void { |
| 362 | self.codesec.delEntry(funcidx); |
| 363 | } |
| 364 | }; |
| 365 | |
| 366 | /// Exports are tricky. We can't leave dead entries in the binary as they |
| 367 | /// would obviously be visible from the execution environment. The simplest |
| 368 | /// way to work around this is to re-emit the export section whenever |
| 369 | /// something changes. This also makes it easier to ensure exported function |
| 370 | /// and global indexes are updated as they change. |
| 371 | const Exports = struct { |
| 372 | exportsec: Section, |
| 373 | /// Size in bytes of the contents of the section. Does not include |
| 374 | /// the "header" containing the section id and this value. |
| 375 | contents_size: u32, |
| 376 | |
| 377 | fn init(file: fs.File, offset: u64, initial_size: u64) !Exports { |
| 378 | return Exports{ |
| 379 | .exportsec = (try VecSection.init(spec.exports_id, file, offset, initial_size)).section, |
| 380 | .contents_size = 5, |
| 381 | }; |
| 382 | } |
| 383 | |
| 384 | fn writeAll(self: *Exports, module: *Module) !void { |
| 385 | const wasm = @fieldParentPtr(Wasm, "exports", self); |
| 386 | const file = wasm.base.file.?; |
| 387 | var buf: [5]u8 = undefined; |
| 388 | |
| 389 | // First ensure the section is the right size |
| 390 | var export_count: u32 = 0; |
| 391 | var new_contents_size: u32 = 5; |
| 392 | for (module.decl_exports.entries.items) |entry| { |
| 393 | for (entry.value) |e| { |
| 394 | export_count += 1; |
| 395 | new_contents_size += calcSize(e); |
| 396 | } |
| 397 | } |
| 398 | if (new_contents_size != self.contents_size) { |
| 399 | try self.exportsec.resize(file, self.contents_size, new_contents_size); |
| 400 | leb.writeUnsignedFixed(5, &buf, new_contents_size); |
| 401 | try file.pwriteAll(&buf, self.exportsec.offset + 1); |
| 402 | } |
| 403 | |
| 404 | try file.seekTo(self.exportsec.offset + Section.header_size); |
| 405 | const writer = file.writer(); |
| 406 | |
| 407 | // Length of the exports vec |
| 408 | leb.writeUnsignedFixed(5, &buf, export_count); |
| 409 | try writer.writeAll(&buf); |
| 410 | |
| 411 | for (module.decl_exports.entries.items) |entry| |
| 412 | for (entry.value) |e| try writeExport(writer, e); |
| 413 | } |
| 414 | |
| 415 | /// Return the total number of bytes an export will take. |
| 416 | /// TODO: fixed-width LEB128 is currently used for simplicity, but should |
| 417 | /// be replaced with proper variable-length LEB128 as it is inefficient. |
| 418 | fn calcSize(e: *Module.Export) u32 { |
| 419 | // LEB128 name length + name bytes + export type + LEB128 index |
| 420 | return 5 + @intCast(u32, e.options.name.len) + 1 + 5; |
| 421 | } |
| 422 | |
| 423 | /// Write the data for a single export to the given file at a given offset. |
| 424 | /// TODO: fixed-width LEB128 is currently used for simplicity, but should |
| 425 | /// be replaced with proper variable-length LEB128 as it is inefficient. |
| 426 | fn writeExport(writer: anytype, e: *Module.Export) !void { |
| 427 | var buf: [5]u8 = undefined; |
| 428 | |
| 429 | // Export name length + name |
| 430 | leb.writeUnsignedFixed(5, &buf, @intCast(u32, e.options.name.len)); |
| 431 | try writer.writeAll(&buf); |
| 432 | try writer.writeAll(e.options.name); |
| 433 | |
| 434 | switch (e.exported_decl.typed_value.most_recent.typed_value.ty.zigTypeTag()) { |
| 435 | .Fn => { |
| 436 | // Type of the export |
| 437 | try writer.writeByte(0x00); |
| 438 | // Exported function index |
| 439 | leb.writeUnsignedFixed(5, &buf, e.exported_decl.fn_link.wasm.?.funcidx); |
| 440 | try writer.writeAll(&buf); |
| 441 | }, |
| 442 | else => return error.TODOImplementNonFnDeclsForWasm, |
| 443 | } |
| 444 | } |
| 445 | }; |
Isaac Freund <mail@isaacfreund.com> 2020-08-07 00:53:55+02:00