1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
//! Support for jitdump files which can be used by perf for profiling jitted code.
//! Spec definitions for the output format is as described here:
//! <https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/tools/perf/Documentation/jitdump-specification.txt>
//!
//! Usage Example:
//!     Record
//!         sudo perf record -k 1 -e instructions:u target/debug/wasmtime -g --jitdump test.wasm
//!     Combine
//!         sudo perf inject -v -j -i perf.data -o perf.jit.data
//!     Report
//!         sudo perf report -i perf.jit.data -F+period,srcline

use std::fmt::Debug;
use std::fs::{File, OpenOptions};
use std::io;
use std::io::Write;
use std::path::Path;
use std::ptr;
use std::{mem, process};

/// Defines jitdump record types
#[repr(u32)]
pub enum RecordId {
    /// Value 0: JIT_CODE_LOAD: record describing a jitted function
    JitCodeLoad = 0,
    /// Value 1: JIT_CODE_MOVE: record describing an already jitted function which is moved
    _JitCodeMove = 1,
    /// Value 2: JIT_CODE_DEBUG_INFO: record describing the debug information for a jitted function
    JitCodeDebugInfo = 2,
    /// Value 3: JIT_CODE_CLOSE: record marking the end of the jit runtime (optional)
    _JitCodeClose = 3,
    /// Value 4: JIT_CODE_UNWINDING_INFO: record describing a function unwinding information
    _JitCodeUnwindingInfo = 4,
}

/// Each record starts with this fixed size record header which describes the record that follows
#[derive(Debug, Default, Clone, Copy)]
#[repr(C)]
pub struct RecordHeader {
    /// uint32_t id: a value identifying the record type (see below)
    pub id: u32,
    /// uint32_t total_size: the size in bytes of the record including the header.
    pub record_size: u32,
    /// uint64_t timestamp: a timestamp of when the record was created.
    pub timestamp: u64,
}

unsafe impl object::Pod for RecordHeader {}

/// The CodeLoadRecord is used for describing jitted functions
#[derive(Debug, Default, Clone, Copy)]
#[repr(C)]
pub struct CodeLoadRecord {
    /// Fixed sized header that describes this record
    pub header: RecordHeader,
    /// `uint32_t pid`: OS process id of the runtime generating the jitted code
    pub pid: u32,
    /// `uint32_t tid`: OS thread identification of the runtime thread generating the jitted code
    pub tid: u32,
    /// `uint64_t vma`: virtual address of jitted code start
    pub virtual_address: u64,
    /// `uint64_t code_addr`: code start address for the jitted code. By default vma = code_addr
    pub address: u64,
    /// `uint64_t code_size`: size in bytes of the generated jitted code
    pub size: u64,
    /// `uint64_t code_index`: unique identifier for the jitted code (see below)
    pub index: u64,
}

unsafe impl object::Pod for CodeLoadRecord {}

/// Describes source line information for a jitted function
#[derive(Debug, Default)]
#[repr(C)]
pub struct DebugEntry {
    /// `uint64_t code_addr`: address of function for which the debug information is generated
    pub address: u64,
    /// `uint32_t line`: source file line number (starting at 1)
    pub line: u32,
    /// `uint32_t discrim`: column discriminator, 0 is default
    pub discriminator: u32,
    /// `char name[n]`: source file name in ASCII, including null termination
    pub filename: String,
}

/// Describes debug information for a jitted function. An array of debug entries are
/// appended to this record during writting. Note, this record must preceed the code
/// load record that describes the same jitted function.
#[derive(Debug, Default, Clone, Copy)]
#[repr(C)]
pub struct DebugInfoRecord {
    /// Fixed sized header that describes this record
    pub header: RecordHeader,
    /// `uint64_t code_addr`: address of function for which the debug information is generated
    pub address: u64,
    /// `uint64_t nr_entry`: number of debug entries for the function appended to this record
    pub count: u64,
}

unsafe impl object::Pod for DebugInfoRecord {}

/// Fixed-sized header for each jitdump file
#[derive(Debug, Default, Clone, Copy)]
#[repr(C)]
pub struct FileHeader {
    /// `uint32_t magic`: a magic number tagging the file type. The value is 4-byte long and represents the
    /// string "JiTD" in ASCII form. It is 0x4A695444 or 0x4454694a depending on the endianness. The field can
    /// be used to detect the endianness of the file
    pub magic: u32,
    /// `uint32_t version`: a 4-byte value representing the format version. It is currently set to 2
    pub version: u32,
    /// `uint32_t total_size`: size in bytes of file header
    pub size: u32,
    /// `uint32_t elf_mach`: ELF architecture encoding (ELF e_machine value as specified in /usr/include/elf.h)
    pub e_machine: u32,
    /// `uint32_t pad1`: padding. Reserved for future use
    pub pad1: u32,
    /// `uint32_t pid`: JIT runtime process identification (OS specific)
    pub pid: u32,
    /// `uint64_t timestamp`: timestamp of when the file was created
    pub timestamp: u64,
    /// `uint64_t flags`: a bitmask of flags
    pub flags: u64,
}

unsafe impl object::Pod for FileHeader {}

/// Interface for driving the creation of jitdump files
pub struct JitDumpFile {
    /// File instance for the jit dump file
    jitdump_file: File,

    map_addr: usize,

    /// Unique identifier for jitted code
    code_index: u64,

    e_machine: u32,
}

impl JitDumpFile {
    /// Intialize a JitDumpAgent and write out the header
    pub fn new(filename: impl AsRef<Path>, e_machine: u32) -> io::Result<Self> {
        let jitdump_file = OpenOptions::new()
            .read(true)
            .write(true)
            .create(true)
            .truncate(true)
            .open(filename.as_ref())?;

        // After we make our `*.dump` file we execute an `mmap` syscall,
        // specifically with executable permissions, to map it into our address
        // space. This is required so `perf inject` will work later. The `perf
        // inject` command will see that an mmap syscall happened, and it'll see
        // the filename we mapped, and that'll trigger it to actually read and
        // parse the file.
        //
        // To match what some perf examples are doing we keep this `mmap` alive
        // until this agent goes away.
        let map_addr = unsafe {
            let ptr = rustix::mm::mmap(
                ptr::null_mut(),
                rustix::param::page_size(),
                rustix::mm::ProtFlags::EXEC | rustix::mm::ProtFlags::READ,
                rustix::mm::MapFlags::PRIVATE,
                &jitdump_file,
                0,
            )?;
            ptr as usize
        };
        let mut state = JitDumpFile {
            jitdump_file,
            map_addr,
            code_index: 0,
            e_machine,
        };
        state.write_file_header()?;
        Ok(state)
    }
}

impl JitDumpFile {
    /// Returns timestamp from a single source
    pub fn get_time_stamp(&self) -> u64 {
        // We need to use `CLOCK_MONOTONIC` on Linux which is what `Instant`
        // conveniently also uses, but `Instant` doesn't allow us to get access
        // to nanoseconds as an internal detail, so we calculate the nanoseconds
        // ourselves here.
        let ts = rustix::time::clock_gettime(rustix::time::ClockId::Monotonic);
        // TODO: What does it mean for either sec or nsec to be negative?
        (ts.tv_sec * 1_000_000_000 + ts.tv_nsec) as u64
    }

    /// Returns the next code index
    pub fn next_code_index(&mut self) -> u64 {
        let code_index = self.code_index;
        self.code_index += 1;
        code_index
    }

    pub fn write_file_header(&mut self) -> io::Result<()> {
        let header = FileHeader {
            timestamp: self.get_time_stamp(),
            e_machine: self.e_machine,
            magic: 0x4A695444,
            version: 1,
            size: mem::size_of::<FileHeader>() as u32,
            pad1: 0,
            pid: process::id(),
            flags: 0,
        };

        self.jitdump_file.write_all(object::bytes_of(&header))?;
        Ok(())
    }

    pub fn write_code_load_record(
        &mut self,
        record_name: &str,
        cl_record: CodeLoadRecord,
        code_buffer: &[u8],
    ) -> io::Result<()> {
        self.jitdump_file.write_all(object::bytes_of(&cl_record))?;
        self.jitdump_file.write_all(record_name.as_bytes())?;
        self.jitdump_file.write_all(b"\0")?;
        self.jitdump_file.write_all(code_buffer)?;
        Ok(())
    }

    /// Write DebugInfoRecord to open jit dump file.
    /// Must be written before the corresponding CodeLoadRecord.
    pub fn write_debug_info_record(&mut self, dir_record: DebugInfoRecord) -> io::Result<()> {
        self.jitdump_file.write_all(object::bytes_of(&dir_record))?;
        Ok(())
    }

    /// Write DebugInfoRecord to open jit dump file.
    /// Must be written before the corresponding CodeLoadRecord.
    pub fn write_debug_info_entries(&mut self, die_entries: Vec<DebugEntry>) -> io::Result<()> {
        for entry in die_entries.iter() {
            self.jitdump_file
                .write_all(object::bytes_of(&entry.address))?;
            self.jitdump_file.write_all(object::bytes_of(&entry.line))?;
            self.jitdump_file
                .write_all(object::bytes_of(&entry.discriminator))?;
            self.jitdump_file.write_all(entry.filename.as_bytes())?;
            self.jitdump_file.write_all(b"\0")?;
        }
        Ok(())
    }

    pub fn dump_code_load_record(
        &mut self,
        method_name: &str,
        addr: *const u8,
        len: usize,
        timestamp: u64,
        pid: u32,
        tid: u32,
    ) -> io::Result<()> {
        let name_len = method_name.len() + 1;
        let size_limit = mem::size_of::<CodeLoadRecord>();

        let rh = RecordHeader {
            id: RecordId::JitCodeLoad as u32,
            record_size: size_limit as u32 + name_len as u32 + len as u32,
            timestamp,
        };

        let clr = CodeLoadRecord {
            header: rh,
            pid,
            tid,
            virtual_address: addr as u64,
            address: addr as u64,
            size: len as u64,
            index: self.next_code_index(),
        };

        unsafe {
            let code_buffer: &[u8] = std::slice::from_raw_parts(addr, len);
            self.write_code_load_record(method_name, clr, code_buffer)
        }
    }
}

impl Drop for JitDumpFile {
    fn drop(&mut self) {
        unsafe {
            rustix::mm::munmap(self.map_addr as *mut _, rustix::param::page_size()).unwrap();
        }
    }
}