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wasm linker: implement __wasm_init_tls synthetic function

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This commit is contained in:
Andrew Kelley 2025-01-14 19:33:36 -08:00
parent f7f8878716
commit c2a918b7a3
1 changed files with 73 additions and 7 deletions
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80
src/link/Wasm/Flush.zig
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@ -297,6 +297,7 @@ pub fn finish(f: *Flush, wasm: *Wasm) !void {
// also notices threadlocal globals from Zcu code.
if (wasm.any_tls_relocs) try wasm.addFunction(.__wasm_apply_global_tls_relocs, &.{}, &.{});
try wasm.addFunction(.__wasm_init_tls, &.{.i32}, &.{});
try wasm.globals.put(gpa, .__tls_base, {});
}
try wasm.tables.ensureUnusedCapacity(gpa, 1);
@ -642,7 +643,7 @@ pub fn finish(f: *Flush, wasm: *Wasm) !void {
section_index += 1;
}
// Global section (used to emit stack pointer)
// Global section.
const globals_len: u32 = @intCast(wasm.globals.entries.len);
if (globals_len > 0) {
const header_offset = try reserveVecSectionHeader(gpa, binary_bytes);
@ -653,9 +654,9 @@ pub fn finish(f: *Flush, wasm: *Wasm) !void {
.__heap_base => try appendGlobal(gpa, binary_bytes, 0, virtual_addrs.heap_base),
.__heap_end => try appendGlobal(gpa, binary_bytes, 0, virtual_addrs.heap_end),
.__stack_pointer => try appendGlobal(gpa, binary_bytes, 1, virtual_addrs.stack_pointer),
.__tls_align => @panic("TODO"),
.__tls_base => @panic("TODO"),
.__tls_size => @panic("TODO"),
.__tls_align => try appendGlobal(gpa, binary_bytes, 0, @intCast(virtual_addrs.tls_align.toByteUnits().?)),
.__tls_base => try appendGlobal(gpa, binary_bytes, 1, virtual_addrs.tls_base.?),
.__tls_size => try appendGlobal(gpa, binary_bytes, 0, virtual_addrs.tls_size.?),
.object_global => |i| {
const global = i.ptr(wasm);
try binary_bytes.appendSlice(gpa, &.{
@ -664,8 +665,8 @@ pub fn finish(f: *Flush, wasm: *Wasm) !void {
});
try emitExpr(wasm, binary_bytes, global.expr);
},
.nav_exe => @panic("TODO"),
.nav_obj => @panic("TODO"),
.nav_exe => unreachable, // Zig source code currently cannot represent this.
.nav_obj => unreachable, // Zig source code currently cannot represent this.
}
}
@ -772,7 +773,11 @@ pub fn finish(f: *Flush, wasm: *Wasm) !void {
defer replaceSize(binary_bytes, code_start);
try emitInitMemoryFunction(wasm, binary_bytes, &virtual_addrs);
},
.__wasm_init_tls => @panic("TODO lower __wasm_init_tls "),
.__wasm_init_tls => {
const code_start = try reserveSize(gpa, binary_bytes);
defer replaceSize(binary_bytes, code_start);
try emitInitTlsFunction(wasm, binary_bytes);
},
.object_function => |i| {
const ptr = i.ptr(wasm);
const code = ptr.code.slice(wasm);
@ -1907,6 +1912,67 @@ fn emitInitMemoryFunction(
binary_bytes.appendAssumeCapacity(@intFromEnum(std.wasm.Opcode.end));
}
fn emitInitTlsFunction(wasm: *const Wasm, bytes: *std.ArrayListUnmanaged(u8)) Allocator.Error!void {
const comp = wasm.base.comp;
const gpa = comp.gpa;
assert(comp.config.shared_memory);
try bytes.ensureUnusedCapacity(gpa, 5 * 10 + 8);
appendReservedUleb32(bytes, 0); // no locals
// If there's a TLS segment, initialize it during runtime using the bulk-memory feature
// TLS segment is always the first one due to how we sort the data segments.
const data_segments = wasm.flush_buffer.data_segments.keys();
if (data_segments.len > 0 and data_segments[0].isTls(wasm)) {
const start_addr = wasm.flush_buffer.data_segments.values()[0];
const end_addr = wasm.flush_buffer.data_segment_groups.items[0].end_addr;
const group_size = end_addr - start_addr;
const data_segment_index = 0;
const param_local: u32 = 0;
bytes.appendAssumeCapacity(@intFromEnum(std.wasm.Opcode.local_get));
appendReservedUleb32(bytes, param_local);
const tls_base_global_index: Wasm.GlobalIndex = @enumFromInt(wasm.globals.getIndex(.__tls_base).?);
bytes.appendAssumeCapacity(@intFromEnum(std.wasm.Opcode.global_set));
appendReservedUleb32(bytes, @intFromEnum(tls_base_global_index));
// load stack values for the bulk-memory operation
{
bytes.appendAssumeCapacity(@intFromEnum(std.wasm.Opcode.local_get));
appendReservedUleb32(bytes, param_local);
bytes.appendAssumeCapacity(@intFromEnum(std.wasm.Opcode.i32_const));
appendReservedUleb32(bytes, 0); //segment offset
bytes.appendAssumeCapacity(@intFromEnum(std.wasm.Opcode.i32_const));
appendReservedUleb32(bytes, group_size); //segment offset
}
// perform the bulk-memory operation to initialize the data segment
bytes.appendAssumeCapacity(@intFromEnum(std.wasm.Opcode.misc_prefix));
appendReservedUleb32(bytes, @intFromEnum(std.wasm.MiscOpcode.memory_init));
// segment immediate
appendReservedUleb32(bytes, data_segment_index);
// memory index immediate (always 0)
appendReservedUleb32(bytes, 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.functions.getIndex(.__wasm_apply_global_tls_relocs)) |function_index| {
const output_function_index: Wasm.OutputFunctionIndex = .fromFunctionIndex(wasm, @enumFromInt(function_index));
bytes.appendAssumeCapacity(@intFromEnum(std.wasm.Opcode.call));
appendReservedUleb32(bytes, @intFromEnum(output_function_index));
}
bytes.appendAssumeCapacity(@intFromEnum(std.wasm.Opcode.end));
}
fn emitStartSection(gpa: Allocator, bytes: *std.ArrayListUnmanaged(u8), i: Wasm.OutputFunctionIndex) !void {
const header_offset = try reserveVecSectionHeader(gpa, bytes);
replaceVecSectionHeader(bytes, header_offset, .start, @intFromEnum(i));