unwindFrameInner

fn unwindFrameInner(si: *SelfInfo, io: Io, context: *UnwindContext) !usize

File

Code

fn unwindFrameInner(si: *SelfInfo, io: Io, context: *UnwindContext) !usize {
    const gpa = std.debug.getDebugInfoAllocator();
    const module = try si.findModule(gpa, io, context.pc);
    defer si.mutex.unlock(io);

    const unwind: *Module.Unwind = try module.getUnwindInfo(gpa);

    const ip_reg_num = comptime Dwarf.ipRegNum(builtin.target.cpu.arch).?;
    const fp_reg_num = comptime Dwarf.fpRegNum(builtin.target.cpu.arch);
    const sp_reg_num = comptime Dwarf.spRegNum(builtin.target.cpu.arch);

    const unwind_info = unwind.unwind_info orelse return error.MissingDebugInfo;
    if (unwind_info.len < @sizeOf(macho.unwind_info_section_header)) return error.InvalidDebugInfo;
    const header: *align(1) const macho.unwind_info_section_header = @ptrCast(unwind_info);

    const index_byte_count = header.indexCount * @sizeOf(macho.unwind_info_section_header_index_entry);
    if (unwind_info.len < header.indexSectionOffset + index_byte_count) return error.InvalidDebugInfo;
    const indices: []align(1) const macho.unwind_info_section_header_index_entry = @ptrCast(unwind_info[header.indexSectionOffset..][0..index_byte_count]);
    if (indices.len == 0) return error.MissingDebugInfo;

    // offset of the PC into the `__TEXT` segment
    const pc_text_offset = context.pc - module.text_base;

    const start_offset: u32, const first_level_offset: u32 = index: {
        var left: usize = 0;
        var len: usize = indices.len;
        while (len > 1) {
            const mid = left + len / 2;
            if (pc_text_offset < indices[mid].functionOffset) {
                len /= 2;
            } else {
                left = mid;
                len -= len / 2;
            }
        }
        break :index .{ indices[left].secondLevelPagesSectionOffset, indices[left].functionOffset };
    };
    // An offset of 0 is a sentinel indicating a range does not have unwind info.
    if (start_offset == 0) return error.MissingDebugInfo;

    const common_encodings_byte_count = header.commonEncodingsArrayCount * @sizeOf(macho.compact_unwind_encoding_t);
    if (unwind_info.len < header.commonEncodingsArraySectionOffset + common_encodings_byte_count) return error.InvalidDebugInfo;
    const common_encodings: []align(1) const macho.compact_unwind_encoding_t = @ptrCast(
        unwind_info[header.commonEncodingsArraySectionOffset..][0..common_encodings_byte_count],
    );

    if (unwind_info.len < start_offset + @sizeOf(macho.UNWIND_SECOND_LEVEL)) return error.InvalidDebugInfo;
    const kind: *align(1) const macho.UNWIND_SECOND_LEVEL = @ptrCast(unwind_info[start_offset..]);

    const entry: struct {
        function_offset: usize,
        raw_encoding: u32,
    } = switch (kind.*) {
        .REGULAR => entry: {
            if (unwind_info.len < start_offset + @sizeOf(macho.unwind_info_regular_second_level_page_header)) return error.InvalidDebugInfo;
            const page_header: *align(1) const macho.unwind_info_regular_second_level_page_header = @ptrCast(unwind_info[start_offset..]);

            const entries_byte_count = page_header.entryCount * @sizeOf(macho.unwind_info_regular_second_level_entry);
            if (unwind_info.len < start_offset + entries_byte_count) return error.InvalidDebugInfo;
            const entries: []align(1) const macho.unwind_info_regular_second_level_entry = @ptrCast(
                unwind_info[start_offset + page_header.entryPageOffset ..][0..entries_byte_count],
            );
            if (entries.len == 0) return error.InvalidDebugInfo;

            var left: usize = 0;
            var len: usize = entries.len;
            while (len > 1) {
                const mid = left + len / 2;
                if (pc_text_offset < entries[mid].functionOffset) {
                    len /= 2;
                } else {
                    left = mid;
                    len -= len / 2;
                }
            }
            break :entry .{
                .function_offset = entries[left].functionOffset,
                .raw_encoding = entries[left].encoding,
            };
        },
        .COMPRESSED => entry: {
            if (unwind_info.len < start_offset + @sizeOf(macho.unwind_info_compressed_second_level_page_header)) return error.InvalidDebugInfo;
            const page_header: *align(1) const macho.unwind_info_compressed_second_level_page_header = @ptrCast(unwind_info[start_offset..]);

            const entries_byte_count = page_header.entryCount * @sizeOf(macho.UnwindInfoCompressedEntry);
            if (unwind_info.len < start_offset + entries_byte_count) return error.InvalidDebugInfo;
            const entries: []align(1) const macho.UnwindInfoCompressedEntry = @ptrCast(
                unwind_info[start_offset + page_header.entryPageOffset ..][0..entries_byte_count],
            );
            if (entries.len == 0) return error.InvalidDebugInfo;

            var left: usize = 0;
            var len: usize = entries.len;
            while (len > 1) {
                const mid = left + len / 2;
                if (pc_text_offset < first_level_offset + entries[mid].funcOffset) {
                    len /= 2;
                } else {
                    left = mid;
                    len -= len / 2;
                }
            }
            const entry = entries[left];

            const function_offset = first_level_offset + entry.funcOffset;
            if (entry.encodingIndex < common_encodings.len) {
                break :entry .{
                    .function_offset = function_offset,
                    .raw_encoding = common_encodings[entry.encodingIndex],
                };
            }

            const local_index = entry.encodingIndex - common_encodings.len;
            const local_encodings_byte_count = page_header.encodingsCount * @sizeOf(macho.compact_unwind_encoding_t);
            if (unwind_info.len < start_offset + page_header.encodingsPageOffset + local_encodings_byte_count) return error.InvalidDebugInfo;
            const local_encodings: []align(1) const macho.compact_unwind_encoding_t = @ptrCast(
                unwind_info[start_offset + page_header.encodingsPageOffset ..][0..local_encodings_byte_count],
            );
            if (local_index >= local_encodings.len) return error.InvalidDebugInfo;
            break :entry .{
                .function_offset = function_offset,
                .raw_encoding = local_encodings[local_index],
            };
        },
        else => return error.InvalidDebugInfo,
    };

    if (entry.raw_encoding == 0) return error.MissingDebugInfo;

    const encoding: macho.CompactUnwindEncoding = @bitCast(entry.raw_encoding);
    const new_ip = switch (builtin.cpu.arch) {
        .x86_64 => switch (encoding.mode.x86_64) {
            .OLD => return error.UnsupportedDebugInfo,
            .RBP_FRAME => ip: {
                const frame = encoding.value.x86_64.frame;

                const fp = (try dwarfRegNative(&context.cpu_state, fp_reg_num)).*;
                const new_sp = fp + 2 * @sizeOf(usize);

                const ip_ptr = fp + @sizeOf(usize);
                const new_ip = @as(*const usize, @ptrFromInt(ip_ptr)).*;
                const new_fp = @as(*const usize, @ptrFromInt(fp)).*;

                (try dwarfRegNative(&context.cpu_state, fp_reg_num)).* = new_fp;
                (try dwarfRegNative(&context.cpu_state, sp_reg_num)).* = new_sp;
                (try dwarfRegNative(&context.cpu_state, ip_reg_num)).* = new_ip;

                const regs: [5]u3 = .{
                    frame.reg0,
                    frame.reg1,
                    frame.reg2,
                    frame.reg3,
                    frame.reg4,
                };
                for (regs, 0..) |reg, i| {
                    if (reg == 0) continue;
                    const addr = fp - frame.frame_offset * @sizeOf(usize) + i * @sizeOf(usize);
                    const reg_number = try Dwarf.compactUnwindToDwarfRegNumber(reg);
                    (try dwarfRegNative(&context.cpu_state, reg_number)).* = @as(*const usize, @ptrFromInt(addr)).*;
                }

                break :ip new_ip;
            },
            .STACK_IMMD,
            .STACK_IND,
            => ip: {
                const frameless = encoding.value.x86_64.frameless;

                const sp = (try dwarfRegNative(&context.cpu_state, sp_reg_num)).*;
                const stack_size: usize = stack_size: {
                    if (encoding.mode.x86_64 == .STACK_IMMD) {
                        break :stack_size @as(usize, frameless.stack.direct.stack_size) * @sizeOf(usize);
                    }
                    // In .STACK_IND, the stack size is inferred from the subq instruction at the beginning of the function.
                    const sub_offset_addr =
                        module.text_base +
                        entry.function_offset +
                        frameless.stack.indirect.sub_offset;
                    // `sub_offset_addr` points to the offset of the literal within the instruction
                    const sub_operand = @as(*align(1) const u32, @ptrFromInt(sub_offset_addr)).*;
                    break :stack_size sub_operand + @sizeOf(usize) * @as(usize, frameless.stack.indirect.stack_adjust);
                };

                // Decode the Lehmer-coded sequence of registers.
                // For a description of the encoding see lib/libc/include/any-macos.13-any/mach-o/compact_unwind_encoding.h

                // Decode the variable-based permutation number into its digits. Each digit represents
                // an index into the list of register numbers that weren't yet used in the sequence at
                // the time the digit was added.
                const reg_count = frameless.stack_reg_count;
                const ip_ptr = ip_ptr: {
                    var digits: [6]u3 = undefined;
                    var accumulator: usize = frameless.stack_reg_permutation;
                    var base: usize = 2;
                    for (0..reg_count) |i| {
                        const div = accumulator / base;
                        digits[digits.len - 1 - i] = @intCast(accumulator - base * div);
                        accumulator = div;
                        base += 1;
                    }

                    var registers: [6]u3 = undefined;
                    var used_indices: [6]bool = @splat(false);
                    for (digits[digits.len - reg_count ..], 0..) |target_unused_index, i| {
                        var unused_count: u8 = 0;
                        const unused_index = for (used_indices, 0..) |used, index| {
                            if (!used) {
                                if (target_unused_index == unused_count) break index;
                                unused_count += 1;
                            }
                        } else unreachable;
                        registers[i] = @intCast(unused_index + 1);
                        used_indices[unused_index] = true;
                    }

                    var reg_addr = sp + stack_size - @sizeOf(usize) * @as(usize, reg_count + 1);
                    for (0..reg_count) |i| {
                        const reg_number = try Dwarf.compactUnwindToDwarfRegNumber(registers[i]);
                        (try dwarfRegNative(&context.cpu_state, reg_number)).* = @as(*const usize, @ptrFromInt(reg_addr)).*;
                        reg_addr += @sizeOf(usize);
                    }

                    break :ip_ptr reg_addr;
                };

                const new_ip = @as(*const usize, @ptrFromInt(ip_ptr)).*;
                const new_sp = ip_ptr + @sizeOf(usize);

                (try dwarfRegNative(&context.cpu_state, sp_reg_num)).* = new_sp;
                (try dwarfRegNative(&context.cpu_state, ip_reg_num)).* = new_ip;

                break :ip new_ip;
            },
            .DWARF => {
                const dwarf = &(unwind.dwarf orelse return error.MissingDebugInfo);
                const rules = try context.computeRules(gpa, dwarf, unwind.vmaddr_slide, encoding.value.x86_64.dwarf);
                return context.next(gpa, &rules);
            },
        },
        .aarch64 => switch (encoding.mode.arm64) {
            .OLD => return error.UnsupportedDebugInfo,
            .FRAMELESS => ip: {
                const sp = (try dwarfRegNative(&context.cpu_state, sp_reg_num)).*;
                const new_sp = sp + encoding.value.arm64.frameless.stack_size * 16;
                const new_ip = (try dwarfRegNative(&context.cpu_state, 30)).*;
                (try dwarfRegNative(&context.cpu_state, sp_reg_num)).* = new_sp;
                break :ip new_ip;
            },
            .DWARF => {
                const dwarf = &(unwind.dwarf orelse return error.MissingDebugInfo);
                const rules = try context.computeRules(gpa, dwarf, unwind.vmaddr_slide, encoding.value.arm64.dwarf);
                return context.next(gpa, &rules);
            },
            .FRAME => ip: {
                const frame = encoding.value.arm64.frame;

                const fp = (try dwarfRegNative(&context.cpu_state, fp_reg_num)).*;
                const ip_ptr = fp + @sizeOf(usize);

                var reg_addr = fp - @sizeOf(usize);
                inline for (@typeInfo(@TypeOf(frame.x_reg_pairs)).@"struct".field_names, 0..) |field_name, i| {
                    if (@field(frame.x_reg_pairs, field_name) != 0) {
                        (try dwarfRegNative(&context.cpu_state, 19 + i)).* = @as(*const usize, @ptrFromInt(reg_addr)).*;
                        reg_addr += @sizeOf(usize);
                        (try dwarfRegNative(&context.cpu_state, 20 + i)).* = @as(*const usize, @ptrFromInt(reg_addr)).*;
                        reg_addr += @sizeOf(usize);
                    }
                }

                // We intentionally skip restoring `frame.d_reg_pairs`; we know we don't support
                // vector registers in the AArch64 `cpu_context` anyway, so there's no reason to
                // fail a legitimate unwind just because we're asked to restore the registers here.
                // If some weird/broken unwind info tells us to read them later, we will fail then.
                reg_addr += 16 * @as(usize, @popCount(@as(u4, @bitCast(frame.d_reg_pairs))));

                const new_ip = @as(*const usize, @ptrFromInt(ip_ptr)).*;
                const new_fp = @as(*const usize, @ptrFromInt(fp)).*;

                (try dwarfRegNative(&context.cpu_state, fp_reg_num)).* = new_fp;
                (try dwarfRegNative(&context.cpu_state, ip_reg_num)).* = new_ip;

                break :ip new_ip;
            },
        },
        else => comptime unreachable, // unimplemented
    };

    const ret_addr = std.debug.stripInstructionPtrAuthCode(new_ip);

    // Like `Dwarf.SelfUnwinder.next`, adjust our next lookup pc in case the `call` was this
    // function's last instruction making `ret_addr` one byte past its end.
    context.pc = ret_addr -| 1;

    return ret_addr;
}