From 9fce1df4cdab57951137c0da2b44fbe6da2442f2 Mon Sep 17 00:00:00 2001 From: Luuk de Gram Date: Fri, 17 Mar 2023 06:32:37 +0100 Subject: wasm-linker: implement runtime TLS relocations --- src/link/Wasm.zig | 63 ++++++++++++++++++++++++++++++++++++++++++++++++ src/link/Wasm/Object.zig | 28 +++++++++++++++++---- src/link/Wasm/types.zig | 12 --------- 3 files changed, 86 insertions(+), 17 deletions(-) (limited to 'src') diff --git a/src/link/Wasm.zig b/src/link/Wasm.zig index 5d4ab2961b..eaaabcc89a 100644 --- a/src/link/Wasm.zig +++ b/src/link/Wasm.zig @@ -139,6 +139,8 @@ archives: std.ArrayListUnmanaged(Archive) = .{}, /// A map of global names (read: offset into string table) to their symbol location globals: std.AutoHashMapUnmanaged(u32, SymbolLoc) = .{}, +/// The list of GOT symbols and their location +got_symbols: std.ArrayListUnmanaged(SymbolLoc) = .{}, /// Maps discarded symbols and their positions to the location of the symbol /// it was resolved to discarded: std.AutoHashMapUnmanaged(SymbolLoc, SymbolLoc) = .{}, @@ -635,6 +637,15 @@ fn parseArchive(wasm: *Wasm, path: []const u8, force_load: bool) !bool { return true; } +fn requiresTLSReloc(wasm: *const Wasm) bool { + for (wasm.got_symbols.items) |loc| { + if (loc.getSymbol(wasm).isTLS()) { + return true; + } + } + return false; +} + fn resolveSymbolsInObject(wasm: *Wasm, object_index: u16) !void { const object: Object = wasm.objects.items[object_index]; log.debug("Resolving symbols in object: '{s}'", .{object.name}); @@ -813,6 +824,48 @@ fn resolveSymbolsInArchives(wasm: *Wasm) !void { } } +fn setupTLSRelocationsFunction(wasm: *Wasm) !void { + // When we have TLS GOT entries and shared memory is enabled, + // we must perform runtime relocations or else we don't create the function. + if (!wasm.base.options.shared_memory or !wasm.requiresTLSReloc()) { + return; + } + + // const loc = try wasm.createSyntheticSymbol("__wasm_apply_global_tls_relocs"); + var function_body = std.ArrayList(u8).init(wasm.base.allocator); + defer function_body.deinit(); + const writer = function_body.writer(); + + // locals (we have none) + try writer.writeByte(0); + for (wasm.got_symbols.items, 0..) |got_loc, got_index| { + const sym: *Symbol = got_loc.getSymbol(wasm); + if (!sym.isTLS()) continue; // only relocate TLS symbols + if (sym.tag == .data and sym.isDefined()) { + // get __tls_base + try writer.writeByte(std.wasm.opcode(.global_get)); + try leb.writeULEB128(writer, wasm.findGlobalSymbol("__tls_base").?.getSymbol(wasm).index); + + // add the virtual address of the symbol + try writer.writeByte(std.wasm.opcode(.i32_const)); + try leb.writeULEB128(writer, sym.virtual_address); + } else if (sym.tag == .function) { + @panic("TODO: relocate GOT entry of function"); + } else continue; + + try writer.writeByte(std.wasm.opcode(.i32_add)); + try writer.writeByte(std.wasm.opcode(.global_set)); + try leb.writeULEB128(writer, wasm.imported_globals_count + @intCast(u32, wasm.wasm_globals.items.len + got_index)); + } + try writer.writeByte(std.wasm.opcode(.end)); + + try wasm.createSyntheticFunction( + "__wasm_apply_global_tls_relocs", + std.wasm.Type{ .params = &.{}, .returns = &.{} }, + &function_body, + ); +} + fn validateFeatures( wasm: *const Wasm, to_emit: *[@typeInfo(types.Feature.Tag).Enum.fields.len]bool, @@ -2083,6 +2136,14 @@ fn initializeTLSFunction(wasm: *Wasm) !void { try leb.writeULEB128(writer, @as(u32, 0)); } + // If we have to perform any TLS relocations, call the corresponding function + // which performs all runtime TLS relocations. This is a synthetic function, + // generated by the linker. + if (wasm.findGlobalSymbol("__wasm_apply_global_tls_relocs")) |loc| { + try writer.writeByte(std.wasm.opcode(.call)); + try leb.writeULEB128(writer, loc.getSymbol(wasm).index); + } + try writer.writeByte(std.wasm.opcode(.end)); try wasm.createSyntheticFunction( @@ -2939,6 +3000,7 @@ fn linkWithZld(wasm: *Wasm, comp: *Compilation, prog_node: *std.Progress.Node) l try wasm.mergeSections(); try wasm.mergeTypes(); try wasm.initializeCallCtorsFunction(); + try wasm.setupTLSRelocationsFunction(); try wasm.initializeTLSFunction(); try wasm.setupExports(); try wasm.writeToFile(enabled_features, emit_features_count, arena); @@ -3059,6 +3121,7 @@ pub fn flushModule(wasm: *Wasm, comp: *Compilation, prog_node: *std.Progress.Nod try wasm.mergeSections(); try wasm.mergeTypes(); try wasm.initializeCallCtorsFunction(); + try wasm.setupTLSRelocationsFunction(); try wasm.initializeTLSFunction(); try wasm.setupExports(); try wasm.writeToFile(enabled_features, emit_features_count, arena); diff --git a/src/link/Wasm/Object.zig b/src/link/Wasm/Object.zig index c2243bdf10..363648971a 100644 --- a/src/link/Wasm/Object.zig +++ b/src/link/Wasm/Object.zig @@ -930,11 +930,29 @@ pub fn parseIntoAtoms(object: *Object, gpa: Allocator, object_index: u16, wasm_b reloc.offset -= relocatable_data.offset; try atom.relocs.append(gpa, reloc); - if (relocation.isTableIndex()) { - try wasm_bin.function_table.put(gpa, .{ - .file = object_index, - .index = relocation.index, - }, 0); + switch (relocation.relocation_type) { + .R_WASM_TABLE_INDEX_I32, + .R_WASM_TABLE_INDEX_I64, + .R_WASM_TABLE_INDEX_SLEB, + .R_WASM_TABLE_INDEX_SLEB64, + => { + try wasm_bin.function_table.put(gpa, .{ + .file = object_index, + .index = relocation.index, + }, 0); + }, + .R_WASM_GLOBAL_INDEX_I32, + .R_WASM_GLOBAL_INDEX_LEB, + => { + const sym = object.symtable[relocation.index]; + if (sym.tag != .global) { + try wasm_bin.got_symbols.append( + wasm_bin.base.allocator, + .{ .file = object_index, .index = relocation.index }, + ); + } + }, + else => {}, } } } diff --git a/src/link/Wasm/types.zig b/src/link/Wasm/types.zig index d19f32b862..801c25e9d9 100644 --- a/src/link/Wasm/types.zig +++ b/src/link/Wasm/types.zig @@ -71,18 +71,6 @@ pub const Relocation = struct { }; } - /// Returns true when the relocation represents a table index relocatable - pub fn isTableIndex(self: Relocation) bool { - return switch (self.relocation_type) { - .R_WASM_TABLE_INDEX_I32, - .R_WASM_TABLE_INDEX_I64, - .R_WASM_TABLE_INDEX_SLEB, - .R_WASM_TABLE_INDEX_SLEB64, - => true, - else => false, - }; - } - pub fn format(self: Relocation, comptime fmt: []const u8, options: std.fmt.FormatOptions, writer: anytype) !void { _ = fmt; _ = options; -- cgit v1.2.3