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trace.ml
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(* This is the implementation of the encoder/decoder for the memtrace format. This format is quite involved, and to understand it it's best to read the CTF specification and comments in memtrace.tsl first. *) (* Increment this when the format changes in an incompatible way *) let memtrace_version = 2 (* If this is true, then all backtraces are immediately decoded and verified after encoding. This is slow, but helpful for debugging. *) let cache_enable_debug = false open Buf exception Parse_error of string let () = Printexc.register_printer (function | Parse_error s -> Some ("malformed trace: " ^ s) | _ -> None) let[@inline never] bad_format s = raise (Parse_error s) let[@inline never] bad_formatf f = Printf.ksprintf (fun s -> bad_format s) f let check_fmt s b = if not b then bad_format s (* Utility types *) (* Time since the epoch *) module Timestamp = struct type t = int64 let of_int64 t = t let to_int64 t = t let to_float t = (Int64.to_float t) /. 1_000_000. let of_float f = f *. 1_000_000. |> Int64.of_float let now () = of_float (Unix.gettimeofday ()) end (* Time since the start of the trace *) module Timedelta = struct type t = int64 let to_int64 t = t let offset = Int64.add end (** CTF packet headers *) (* Small enough that Unix.write still does single writes. (i.e. below 64k) *) let max_packet_size = 1 lsl 15 type packet_header_info = { content_size: int; (* bytes, excluding header *) time_begin : Timestamp.t; time_end : Timestamp.t; alloc_id_begin : Int64.t; alloc_id_end : Int64.t; pid : Int64.t; version : int } (* When writing a packet, some fields can be filled in only once the packet is complete. *) type ctf_header_offsets = { off_packet_size : Write.position_32; off_timestamp_begin : Write.position_64; off_timestamp_end : Write.position_64; off_flush_duration : Write.position_32; off_alloc_begin : Write.position_64; off_alloc_end : Write.position_64 } let put_ctf_header b pid cache = let open Write in put_32 b 0xc1fc1fc1l; let off_packet_size = skip_32 b in let off_timestamp_begin = skip_64 b in let off_timestamp_end = skip_64 b in let off_flush_duration = skip_32 b in put_16 b memtrace_version; put_64 b pid; begin match cache with | Some c -> Backtrace_codec.Writer.put_cache_verifier c b | None -> Backtrace_codec.Writer.put_dummy_verifier b end; let off_alloc_begin = skip_64 b in let off_alloc_end = skip_64 b in {off_packet_size; off_timestamp_begin; off_timestamp_end; off_flush_duration; off_alloc_begin; off_alloc_end} let finish_ctf_header hdr b ~timestamp_begin ~timestamp_end ~alloc_id_begin ~alloc_id_end = let open Write in let size = b.pos in update_32 b hdr.off_packet_size (Int32.mul (Int32.of_int size) 8l); update_64 b hdr.off_timestamp_begin timestamp_begin; update_64 b hdr.off_timestamp_end timestamp_end; (* CR-someday sdolan: is flush duration useful? *) update_32 b hdr.off_flush_duration 0l; update_64 b hdr.off_alloc_begin (Int64.of_int alloc_id_begin); update_64 b hdr.off_alloc_end (Int64.of_int alloc_id_end) let get_ctf_header b rcache = let open Read in let start = b.pos in let magic = get_32 b in let packet_size = get_32 b in let time_begin = get_64 b in let time_end = get_64 b in let _flush_duration = get_32 b in let version = get_16 b in let pid = get_64 b in begin match rcache with | Some c -> if not (Backtrace_codec.Reader.check_cache_verifier c b) then bad_format "cache verification" | None -> Backtrace_codec.Reader.skip_cache_verifier b end; let alloc_id_begin = get_64 b in let alloc_id_end = get_64 b in check_fmt "Not a CTF packet" (magic = 0xc1fc1fc1l); begin match version, memtrace_version with | v, v' when v = v' -> () | 1, 2 -> (* The only difference between v001 and v002 is the presence of the context field in trace_info. get_trace_info can parse either. *) () | v, v' -> bad_formatf "trace format v%03d, but expected v%03d" v v' end; check_fmt "Bad packet size" (packet_size >= 0l); check_fmt "Monotone packet timestamps" (time_begin <= time_end); check_fmt "Monotone alloc IDs" (alloc_id_begin <= alloc_id_end); let header_size = b.pos - start in { content_size = Int32.(to_int (div packet_size 8l) - header_size); time_begin; time_end; alloc_id_begin; alloc_id_end; pid; version } (** Event headers *) type evcode = | Ev_trace_info | Ev_location | Ev_alloc | Ev_promote | Ev_collect | Ev_short_alloc of int let event_code = function | Ev_trace_info -> 0 | Ev_location -> 1 | Ev_alloc -> 2 | Ev_promote -> 3 | Ev_collect -> 4 | Ev_short_alloc n -> assert (1 <= n && n <= 16); 100 + n let event_of_code = function | 0 -> Ev_trace_info | 1 -> Ev_location | 2 -> Ev_alloc | 3 -> Ev_promote | 4 -> Ev_collect | n when 101 <= n && n <= 116 -> Ev_short_alloc (n - 100) | c -> bad_format ("Unknown event code " ^ string_of_int c) let event_header_time_len = 25 let event_header_time_mask = 0x1ffffffl (* NB: packet_max_time is less than (1 lsl event_header_time_len) microsecs *) let packet_max_time = 30 * 1_000_000 let put_event_header b ev time = let open Write in let code = Int32.(logor (shift_left (of_int (event_code ev)) event_header_time_len) (logand (Int64.to_int32 time) event_header_time_mask)) in put_32 b code let[@inline] get_event_header info b = let open Read in let code = get_32 b in let start_low = Int32.logand event_header_time_mask (Int64.to_int32 info.time_begin) in let time_low = Int32.logand event_header_time_mask code in let time_low = if time_low < start_low then (* Overflow *) Int32.(add time_low (of_int (1 lsl event_header_time_len))) else time_low in let time = Int64.(add (logand info.time_begin (lognot (of_int32 event_header_time_mask))) (of_int32 time_low)) in check_fmt "time in packet bounds" (info.time_begin <= time && time <= info.time_end); let ev = event_of_code (Int32.(to_int (shift_right_logical code event_header_time_len))) in (ev, time) module Location = Location_codec.Location (** Trace info *) module Info = struct type t = { sample_rate : float; word_size : int; executable_name : string; host_name : string; ocaml_runtime_params : string; pid : Int64.t; start_time : Timestamp.t; context : string option; } end let put_trace_info b (info : Info.t) = let open Write in put_event_header b Ev_trace_info info.start_time; put_float b info.sample_rate; put_8 b info.word_size; put_string b info.executable_name; put_string b info.host_name; put_string b info.ocaml_runtime_params; put_64 b info.pid; let context = match info.context with None -> "" | Some s -> s in put_string b context let get_trace_info b ~packet_info = let open Read in let start_time = packet_info.time_begin in let sample_rate = get_float b in let word_size = get_8 b in let executable_name = get_string b in let host_name = get_string b in let ocaml_runtime_params = get_string b in let pid = get_64 b in let context = if packet_info.version >= 2 then match get_string b with | "" -> None | s -> Some s else None in { Info.start_time; sample_rate; word_size; executable_name; host_name; ocaml_runtime_params; pid; context } (** Trace writer *) type writer = { dest : Unix.file_descr; pid : int64; getpid : unit -> int64; loc_writer : Location_codec.Writer.t; cache : Backtrace_codec.Writer.t; debug_reader_cache : Backtrace_codec.Reader.t option; (* Locations that missed cache in this packet *) mutable new_locs : (int * Location.t list) array; mutable new_locs_len : int; new_locs_buf : Bytes.t; (* Last allocation callstack *) mutable last_callstack : int array; mutable start_alloc_id : int; (* alloc ID at start of packet *) mutable next_alloc_id : int; mutable packet_time_start : Timestamp.t; mutable packet_time_end : Timestamp.t; mutable packet_header : ctf_header_offsets; mutable packet : Write.t; } let make_writer dest ?getpid (info : Info.t) = let open Write in let getpid = match getpid with | Some getpid -> getpid | None -> fun () -> info.pid in let pid = getpid () in let packet = Write.of_bytes (Bytes.make max_packet_size '\042') in begin (* Write the trace info packet *) let hdr = put_ctf_header packet pid None in put_trace_info packet info; finish_ctf_header hdr packet ~timestamp_begin:info.start_time ~timestamp_end:info.start_time ~alloc_id_begin:0 ~alloc_id_end:0; write_fd dest packet; end; let packet = Write.of_bytes packet.buf in let packet_header = put_ctf_header packet pid None in let cache = Backtrace_codec.Writer.create () in let debug_reader_cache = if cache_enable_debug then Some (Backtrace_codec.Reader.create ()) else None in let s = { dest; pid; getpid; loc_writer = Location_codec.Writer.create (); new_locs = [| |]; new_locs_len = 0; new_locs_buf = Bytes.make max_packet_size '\042'; cache = cache; debug_reader_cache; last_callstack = [| |]; next_alloc_id = 0; start_alloc_id = 0; packet_time_start = info.start_time; packet_time_end = info.start_time; packet_header; packet } in s module IntTbl = Hashtbl.MakeSeeded (struct type t = int let hash _seed (id : t) = let h = id * 189696287 in h lxor (h lsr 23) let equal (a : t) (b : t) = a = b end) module Obj_id = struct type t = int module Tbl = IntTbl end module Location_code = struct type t = int module Tbl = IntTbl end module Allocation_source = struct type t = Minor | Major | External end module Event = struct type t = | Alloc of { obj_id : Obj_id.t; length : int; nsamples : int; source : Allocation_source.t; backtrace_buffer : Location_code.t array; backtrace_length : int; common_prefix : int; } | Promote of Obj_id.t | Collect of Obj_id.t let to_string decode_loc = function | Alloc {obj_id; length; nsamples; source; backtrace_buffer; backtrace_length; common_prefix} -> let backtrace = List.init backtrace_length (fun i -> let s = backtrace_buffer.(i) in match decode_loc s with | [] -> Printf.sprintf "$%d" (s :> int) | ls -> String.concat " " (List.map Location.to_string ls)) |> String.concat " " in let alloc_src = match source with | Minor -> "alloc" | Major -> "alloc_major" | External -> "alloc_ext" in Printf.sprintf "%010d %s %d len=%d % 4d: %s" (obj_id :> int) alloc_src nsamples length common_prefix backtrace; | Promote id -> Printf.sprintf "%010d promote" (id :> int) | Collect id -> Printf.sprintf "%010d collect" (id :> int) end let log_new_loc s loc = let alen = Array.length s.new_locs in assert (s.new_locs_len <= alen); if s.new_locs_len = alen then begin let new_len = if alen = 0 then 32 else alen * 2 in let locs = Array.make new_len loc in Array.blit s.new_locs 0 locs 0 alen; s.new_locs <- locs; s.new_locs_len <- alen + 1 end else begin s.new_locs.(s.new_locs_len) <- loc; s.new_locs_len <- s.new_locs_len + 1 end (** Flushing *) exception Pid_changed let flush_at s ~now = (* If the PID has changed, then the process forked and we're in the subprocess. Don't write anything to the file, and raise an exception to quit tracing *) if s.pid <> s.getpid () then raise Pid_changed; let open Write in (* First, flush newly-seen locations. These must be emitted before any events that might refer to them *) let i = ref 0 in while !i < s.new_locs_len do let b = Write.of_bytes s.new_locs_buf in let hdr = put_ctf_header b s.pid None in while !i < s.new_locs_len && remaining b > Location_codec.Writer.max_length do put_event_header b Ev_location s.packet_time_start; Location_codec.Writer.put_location s.loc_writer b s.new_locs.(!i); incr i done; finish_ctf_header hdr b ~timestamp_begin:s.packet_time_start ~timestamp_end:s.packet_time_start ~alloc_id_begin:s.start_alloc_id ~alloc_id_end:s.start_alloc_id; write_fd s.dest b done; (* Next, flush the actual events *) finish_ctf_header s.packet_header s.packet ~timestamp_begin:s.packet_time_start ~timestamp_end:s.packet_time_end ~alloc_id_begin:s.start_alloc_id ~alloc_id_end:s.next_alloc_id; write_fd s.dest s.packet; (* Finally, reset the buffer *) s.packet_time_start <- now; s.packet_time_end <- now; s.new_locs_len <- 0; s.packet <- Write.of_bytes s.packet.buf; s.start_alloc_id <- s.next_alloc_id; s.packet_header <- put_ctf_header s.packet s.pid (Some s.cache) let max_ev_size = 100 (* upper bound on fixed-size portion of events (i.e. not backtraces or locations) *) + max Location_codec.Writer.max_length Backtrace_codec.Writer.max_length let begin_event s ev ~(now : Timestamp.t) = let open Write in if remaining s.packet < max_ev_size || s.new_locs_len > 128 || Int64.(sub now s.packet_time_start > of_int packet_max_time) then flush_at s ~now; s.packet_time_end <- now; put_event_header s.packet ev now let flush s = flush_at s ~now:s.packet_time_end let find_common_suffix (prev : int array) (curr : int array) = let i = ref (Array.length curr - 1) and j = ref (Array.length prev - 1) in while !i >= 0 && !j >= 0 do if Array.unsafe_get curr !i = Array.unsafe_get prev !j then begin decr i; decr j end else begin j := -1 end done; !i type alloc_length_format = | Len_short of Write.position_8 | Len_long of Write.position_16 let put_alloc s now ~length ~nsamples ~source ~callstack ~callstack_as_ints ~decode_callstack_entry = let open Write in let suff = find_common_suffix s.last_callstack callstack_as_ints in s.last_callstack <- callstack_as_ints; let is_short = 1 <= length && length <= 16 && source = Allocation_source.Minor && nsamples = 1 && suff < 255 in begin_event s (if is_short then Ev_short_alloc length else Ev_alloc) ~now; let id = s.next_alloc_id in s.next_alloc_id <- id + 1; let cache = s.cache in let b = s.packet in let common_pfx_len = Array.length callstack_as_ints - 1 - suff in let src_code = match source with | Minor -> 0 | Major -> 1 | External -> 2 in let bt_len_off = if is_short then begin put_vint b common_pfx_len; Len_short (skip_8 b) end else begin put_vint b length; put_vint b nsamples; put_8 b src_code; put_vint b common_pfx_len; Len_long (skip_16 b) end in let bt_elem_off = b.pos in let log_new_location ~index = log_new_loc s (callstack_as_ints.(index), decode_callstack_entry callstack index) in let nencoded = Backtrace_codec.Writer.put_backtrace cache b ~alloc_id:id ~callstack:callstack_as_ints ~callstack_len:suff ~log_new_location in begin match bt_len_off with | Len_short p -> assert (nencoded <= 0xff); update_8 b p nencoded | Len_long p -> (* This can't overflow because there isn't room in a packet for more than 0xffff entries. (See max_packet_size) *) assert (nencoded <= 0xffff); update_16 b p nencoded end; begin match s.debug_reader_cache with | None -> () | Some c -> let open Read in (* Decode the backtrace and check that it matches *) let b' = Read.of_bytes_sub b.buf ~pos:bt_elem_off ~pos_end:b.pos in let decoded, decoded_len = Backtrace_codec.Reader.get_backtrace c b' ~nencoded ~common_pfx_len in assert (remaining b' = 0); let rev_callstack = callstack_as_ints |> Array.to_list |> List.rev |> Array.of_list in if (Array.sub decoded 0 decoded_len) <> rev_callstack then begin rev_callstack |> Array.map Int64.of_int |> Array.iter (Printf.printf " %08Lx"); Printf.printf " !\n%!"; Array.sub decoded 0 decoded_len |> Array.iter (Printf.printf " %08x"); Printf.printf " !\n%!"; failwith "bad coded backtrace" end end; id let get_alloc ~parse_backtraces evcode cache alloc_id b = let open Read in let is_short, length, nsamples, source = match evcode with | Ev_short_alloc n -> true, n, 1, Allocation_source.Minor | Ev_alloc -> begin let length = get_vint b in let nsamples = get_vint b in let source : Allocation_source.t = match get_8 b with | 0 -> Minor | 1 -> Major | 2 -> External | _ -> bad_format "source" in false, length, nsamples, source end | _ -> assert false in let common_pfx_len = get_vint b in let nencoded = if is_short then get_8 b else get_16 b in let (backtrace_buffer, backtrace_length) = if parse_backtraces then Backtrace_codec.Reader.get_backtrace cache b ~nencoded ~common_pfx_len else begin Backtrace_codec.Reader.skip_backtrace cache b ~nencoded ~common_pfx_len; [| |], 0 end in Event.Alloc { obj_id = alloc_id; length; nsamples; source; backtrace_buffer; backtrace_length; common_prefix=common_pfx_len } (* The other events are much simpler *) let put_promote s now id = let open Write in if id >= s.next_alloc_id then raise (Invalid_argument "Invalid ID in promotion"); begin_event s Ev_promote ~now; let b = s.packet in put_vint b (s.next_alloc_id - 1 - id) let get_promote alloc_id b = let open Read in let id_delta = get_vint b in check_fmt "promote id sync" (id_delta >= 0); let id = alloc_id - 1 - id_delta in Event.Promote id let put_collect s now id = let open Write in if id >= s.next_alloc_id then raise (Invalid_argument "Invalid ID in collection"); begin_event s Ev_collect ~now; let b = s.packet in put_vint b (s.next_alloc_id - 1 - id) let get_collect alloc_id b = let open Read in let id_delta = get_vint b in check_fmt "collect id sync" (id_delta >= 0); let id = alloc_id - 1 - id_delta in Event.Collect id (** Trace reader *) type reader = { fd : Unix.file_descr; info : Info.t; data_off : int; loc_table : Location.t list Location_code.Tbl.t; } let make_reader fd = let open Read in let buf = Bytes.make max_packet_size '\042' in let start_pos = Unix.lseek fd 0 SEEK_CUR in let b = read_fd fd buf in let packet_info = get_ctf_header b None in let header_size = b.pos in let (b, _) = split b packet_info.content_size in check_fmt "trace info packet size" (remaining b >= packet_info.content_size); let ev, evtime = get_event_header packet_info b in check_fmt "trace info packet code" (ev = Ev_trace_info); check_fmt "trace info packet time" (evtime = packet_info.time_begin); let trace_info = get_trace_info b ~packet_info in check_fmt "trace info packet done" (remaining b = 0); let loc_table = Location_code.Tbl.create 20 in let data_off = start_pos + header_size + packet_info.content_size in { fd; info = trace_info; data_off; loc_table; } let report_hack fmt = Printf.kfprintf (fun ppf -> Printf.fprintf ppf "\n%!") stderr fmt let refill_to size fd stream = let open Read in if remaining stream < size then refill_fd fd stream else stream let iter s ?(parse_backtraces=true) f = let open Read in let cache = Backtrace_codec.Reader.create () in let loc_reader = Location_codec.Reader.create () in let last_timestamp = ref s.info.start_time in let alloc_id = ref 0 in let iter_events_of_packet packet_header b = while remaining b > 0 do let (ev, time) = get_event_header packet_header b in check_fmt "monotone timestamps" (!last_timestamp <= time); last_timestamp := time; let dt = Int64.(sub time s.info.start_time) in begin match ev with | Ev_trace_info -> bad_format "Multiple trace-info events present" | Ev_location -> let (id, loc) = Location_codec.Reader.get_location loc_reader b in (*Printf.printf "%3d _ _ location\n" (b.pos - last_pos);*) begin if Location_code.Tbl.mem s.loc_table id then check_fmt "consistent location info" (Location_code.Tbl.find s.loc_table id = loc) else Location_code.Tbl.add s.loc_table id loc end | (Ev_alloc | Ev_short_alloc _) as evcode -> let info = get_alloc ~parse_backtraces evcode cache !alloc_id b in incr alloc_id; (*Printf.printf "%3d " (b.pos - last_pos);*) f dt info | Ev_collect -> let info = get_collect !alloc_id b in (*Printf.printf "%3d " (b.pos - last_pos);*) f dt info | Ev_promote -> let info = get_promote !alloc_id b in (*Printf.printf "%3d " (b.pos - last_pos);*) f dt info end done; check_fmt "alloc id sync" (packet_header.alloc_id_end = Int64.of_int !alloc_id) in Unix.lseek s.fd s.data_off SEEK_SET |> ignore; let rec iter_packets stream = let header_upper_bound = 200 (* more than big enough for a header *) in let stream = refill_to header_upper_bound s.fd stream in if remaining stream = 0 then () else let packet_header = get_ctf_header stream (if parse_backtraces then Some cache else None) in let stream = refill_to packet_header.content_size s.fd stream in let (packet, rest) = split stream packet_header.content_size in if !last_timestamp <= packet_header.time_begin && !alloc_id = Int64.to_int packet_header.alloc_id_begin then begin if packet_header.pid <> s.info.pid then report_hack "skipping bad packet (wrong pid: %Ld, but tracing %Ld)" packet_header.pid s.info.pid else if remaining packet <> packet_header.content_size then report_hack "skipping truncated packet" else iter_events_of_packet packet_header packet end else begin report_hack "skipping bad packet at id %d %Ld-%Ld" !alloc_id packet_header.alloc_id_begin packet_header.alloc_id_end end; iter_packets rest in iter_packets (read_fd s.fd (Bytes.make max_packet_size '\000')) module Writer = struct type t = writer exception Pid_changed = Pid_changed let create = make_writer (* Unfortunately, efficient access to the backtrace is not possible with the current Printexc API, even though internally it's an int array. For now, wave the Obj.magic wand. There's a PR to fix this: https://github.com/ocaml/ocaml/pull/9663 *) let location_code_array_of_raw_backtrace (b : Printexc.raw_backtrace) = (Obj.magic b : Location_code.t array) let decode_raw_backtrace_entry callstack i : Location.t list = let open Printexc in let rec get_locations slot : Location.t list = let tail = match get_raw_backtrace_next_slot slot with | None -> [] | Some slot -> get_locations slot in let slot = convert_raw_backtrace_slot slot in match Slot.location slot with | None -> tail | Some { filename; line_number; start_char; end_char } -> let defname = match Slot.name slot with Some n -> n | _ -> "??" in { filename; line=line_number; start_char; end_char; defname }::tail in get_locations (get_raw_backtrace_slot callstack i) |> List.rev let put_alloc_with_raw_backtrace t now ~length ~nsamples ~source ~callstack = let callstack_as_ints = location_code_array_of_raw_backtrace callstack in put_alloc t now ~length ~nsamples ~source ~callstack ~callstack_as_ints ~decode_callstack_entry:decode_raw_backtrace_entry let put_alloc t now ~length ~nsamples ~source ~callstack ~decode_callstack_entry = let decode_callstack_entry cs i = decode_callstack_entry cs.(i) in put_alloc t now ~length ~nsamples ~source ~callstack ~callstack_as_ints:callstack ~decode_callstack_entry let put_collect = put_collect let put_promote = put_promote let flush = flush let close t = flush t; Unix.close t.dest let put_event w ~decode_callstack_entry now (ev : Event.t) = match ev with | Alloc { obj_id; length; nsamples; source; backtrace_buffer; backtrace_length; common_prefix = _ } -> let btrev = Array.init backtrace_length (fun i -> backtrace_buffer.(backtrace_length - 1 - i)) in let id = put_alloc w now ~length ~nsamples ~source ~callstack:btrev ~decode_callstack_entry in if id <> obj_id then raise (Invalid_argument "Incorrect allocation ID") | Promote id -> put_promote w now id | Collect id -> put_collect w now id end module Reader = struct type t = reader let create = make_reader let info s = s.info let lookup_location_code { loc_table; _ } code = match Location_code.Tbl.find loc_table code with | v -> v | exception Not_found -> raise (Invalid_argument (Printf.sprintf "invalid location code %08x" code)) let iter = iter let open_ ~filename = make_reader (Unix.openfile filename [Unix.O_RDONLY] 0) let size_bytes s = (Unix.LargeFile.fstat s.fd).st_size let close s = Unix.close s.fd end