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mod cast;
use std::collections::BTreeMap;
use std::fmt;
use std::io::BufRead;
use std::io::Write;
use std::path::PathBuf;
use std::time::{Instant, SystemTime, UNIX_EPOCH};
use anyhow::bail;
use flate2::write::GzEncoder;
use flate2::Compression;
use prost::Message;
pub use cast::CastFrom;
pub use cast::TryCastFrom;
/// Start times of the profiler.
#[derive(Copy, Clone, Debug)]
pub enum ProfStartTime {
Instant(Instant),
TimeImmemorial,
}
/// Helper struct to simplify building a `string_table` for the pprof format.
#[derive(Default)]
struct StringTable(BTreeMap<String, i64>);
impl StringTable {
fn new() -> Self {
// Element 0 must always be the emtpy string.
let inner = [("".into(), 0)].into();
Self(inner)
}
fn insert(&mut self, s: &str) -> i64 {
if let Some(idx) = self.0.get(s) {
*idx
} else {
let idx = i64::try_from(self.0.len()).expect("must fit");
self.0.insert(s.into(), idx);
idx
}
}
fn finish(self) -> Vec<String> {
let mut vec: Vec<_> = self.0.into_iter().collect();
vec.sort_by_key(|(_, idx)| *idx);
vec.into_iter().map(|(s, _)| s).collect()
}
}
#[path = "perftools.profiles.rs"]
mod pprof_types;
/// A single sample in the profile. The stack is a list of addresses.
#[derive(Clone, Debug)]
pub struct WeightedStack {
pub addrs: Vec<usize>,
pub weight: f64,
}
/// A mapping of a single shared object.
#[derive(Clone, Debug)]
pub struct Mapping {
pub memory_start: usize,
pub memory_end: usize,
pub memory_offset: usize,
pub file_offset: u64,
pub pathname: PathBuf,
pub build_id: Option<BuildId>,
}
/// Build ID of a shared object.
#[derive(Clone, Debug, PartialEq, Eq, PartialOrd, Ord)]
pub struct BuildId(pub Vec<u8>);
impl fmt::Display for BuildId {
fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
for byte in &self.0 {
write!(f, "{byte:02x}")?;
}
Ok(())
}
}
/// A minimal representation of a profile that can be parsed from the jemalloc heap profile.
#[derive(Default)]
pub struct StackProfile {
pub annotations: Vec<String>,
// The second element is the index in `annotations`, if one exists.
pub stacks: Vec<(WeightedStack, Option<usize>)>,
pub mappings: Vec<Mapping>,
}
impl StackProfile {
/// Converts the profile into the pprof format.
///
/// pprof encodes profiles as gzipped protobuf messages of the Profile message type
/// (see `pprof/profile.proto`).
pub fn to_pprof(
&self,
sample_type: (&str, &str),
period_type: (&str, &str),
anno_key: Option<String>,
) -> Vec<u8> {
use crate::pprof_types as proto;
let mut profile = proto::Profile::default();
let mut strings = StringTable::new();
let anno_key = anno_key.unwrap_or_else(|| "annotation".into());
profile.sample_type = vec![proto::ValueType {
r#type: strings.insert(sample_type.0),
unit: strings.insert(sample_type.1),
}];
profile.period_type = Some(proto::ValueType {
r#type: strings.insert(period_type.0),
unit: strings.insert(period_type.1),
});
profile.time_nanos = SystemTime::now()
.duration_since(UNIX_EPOCH)
.expect("now is later than UNIX epoch")
.as_nanos()
.try_into()
.expect("the year 2554 is far away");
for (mapping, mapping_id) in self.mappings.iter().zip(1..) {
let pathname = mapping.pathname.to_string_lossy();
let filename_idx = strings.insert(&pathname);
let build_id_idx = match &mapping.build_id {
Some(build_id) => strings.insert(&build_id.to_string()),
None => 0,
};
profile.mapping.push(proto::Mapping {
id: mapping_id,
memory_start: u64::cast_from(mapping.memory_start),
memory_limit: u64::cast_from(mapping.memory_end),
file_offset: mapping.file_offset,
filename: filename_idx,
build_id: build_id_idx,
..Default::default()
});
// This is a is a Polar Signals-specific extension: For correct offline symbolization
// they need access to the memory offset of mappings, but the pprof format only has a
// field for the file offset. So we instead encode additional information about
// mappings in magic comments. There must be exactly one comment for each mapping.
// Take a shortcut and assume the ELF type is always `ET_DYN`. This is true for shared
// libraries and for position-independent executable, so it should always be true for
// any mappings we have.
// Getting the actual information is annoying. It's in the ELF header (the `e_type`
// field), but there is no guarantee that the full ELF header gets mapped, so we might
// not be able to find it in memory. We could try to load it from disk instead, but
// then we'd have to worry about blocking disk I/O.
let elf_type = 3;
let comment = format!(
"executableInfo={:x};{:x};{:x}",
elf_type, mapping.file_offset, mapping.memory_offset
);
profile.comment.push(strings.insert(&comment));
}
let mut location_ids = BTreeMap::new();
for (stack, anno) in self.iter() {
let mut sample = proto::Sample::default();
let value = stack.weight.trunc();
let value = i64::try_cast_from(value).expect("no exabyte heap sizes");
sample.value.push(value);
for addr in stack.addrs.iter().rev() {
// See the comment
// [here](https://github.com/rust-lang/backtrace-rs/blob/036d4909e1fb9c08c2bb0f59ac81994e39489b2f/src/symbolize/mod.rs#L123-L147)
// for why we need to subtract one. tl;dr addresses
// in stack traces are actually the return address of
// the called function, which is one past the call
// itself.
//
// Of course, the `call` instruction can be more than one byte, so after subtracting
// one, we might point somewhere in the middle of it, rather
// than to the beginning of the instruction. That's fine; symbolization
// tools don't seem to get confused by this.
let addr = u64::cast_from(*addr) - 1;
let loc_id = *location_ids.entry(addr).or_insert_with(|| {
// pprof_types.proto says the location id may be the address, but Polar Signals
// insists that location ids are sequential, starting with 1.
let id = u64::cast_from(profile.location.len()) + 1;
let mapping_id = profile
.mapping
.iter()
.find(|m| m.memory_start <= addr && m.memory_limit > addr)
.map_or(0, |m| m.id);
profile.location.push(proto::Location {
id,
mapping_id,
address: addr,
..Default::default()
});
id
});
sample.location_id.push(loc_id);
if let Some(anno) = anno {
sample.label.push(proto::Label {
key: strings.insert(&anno_key),
str: strings.insert(anno),
..Default::default()
})
}
}
profile.sample.push(sample);
}
profile.string_table = strings.finish();
let encoded = profile.encode_to_vec();
let mut gz = GzEncoder::new(Vec::new(), Compression::default());
gz.write_all(&encoded).unwrap();
gz.finish().unwrap()
}
}
pub struct StackProfileIter<'a> {
inner: &'a StackProfile,
idx: usize,
}
impl<'a> Iterator for StackProfileIter<'a> {
type Item = (&'a WeightedStack, Option<&'a str>);
fn next(&mut self) -> Option<Self::Item> {
let (stack, anno) = self.inner.stacks.get(self.idx)?;
self.idx += 1;
let anno = anno.map(|idx| self.inner.annotations.get(idx).unwrap().as_str());
Some((stack, anno))
}
}
impl StackProfile {
pub fn push_stack(&mut self, stack: WeightedStack, annotation: Option<&str>) {
let anno_idx = if let Some(annotation) = annotation {
Some(
self.annotations
.iter()
.position(|anno| annotation == anno.as_str())
.unwrap_or_else(|| {
self.annotations.push(annotation.to_string());
self.annotations.len() - 1
}),
)
} else {
None
};
self.stacks.push((stack, anno_idx))
}
pub fn push_mapping(&mut self, mapping: Mapping) {
self.mappings.push(mapping);
}
pub fn iter(&self) -> StackProfileIter<'_> {
StackProfileIter {
inner: self,
idx: 0,
}
}
}
/// Parse a jemalloc profile file, producing a vector of stack traces along with their weights.
pub fn parse_jeheap<R: BufRead>(
r: R,
mappings: Option<&[Mapping]>,
) -> anyhow::Result<StackProfile> {
let mut cur_stack = None;
let mut profile = StackProfile::default();
let mut lines = r.lines();
let first_line = match lines.next() {
Some(s) => s?,
None => bail!("Heap dump file was empty"),
};
// The first line of the file should be e.g. "heap_v2/524288", where the trailing
// number is the inverse probability of a byte being sampled.
let sampling_rate: f64 = str::parse(first_line.trim_start_matches("heap_v2/"))?;
for line in &mut lines {
let line = line?;
let line = line.trim();
let words: Vec<_> = line.split_ascii_whitespace().collect();
if !words.is_empty() && words[0] == "@" {
if cur_stack.is_some() {
bail!("Stack without corresponding weight!")
}
let mut addrs = words[1..]
.iter()
.map(|w| {
let raw = w.trim_start_matches("0x");
usize::from_str_radix(raw, 16)
})
.collect::<Result<Vec<_>, _>>()?;
addrs.reverse();
cur_stack = Some(addrs);
}
if words.len() > 2 && words[0] == "t*:" {
if let Some(addrs) = cur_stack.take() {
// The format here is e.g.:
// t*: 40274: 2822125696 [0: 0]
//
// "t*" means summary across all threads; someday we will support per-thread dumps but don't now.
// "40274" is the number of sampled allocations (`n_objs` here).
// On all released versions of jemalloc, "2822125696" is the total number of bytes in those allocations.
//
// To get the predicted number of total bytes from the sample, we need to un-bias it by following the logic in
// jeprof's `AdjustSamples`: https://github.com/jemalloc/jemalloc/blob/498f47e1ec83431426cdff256c23eceade41b4ef/bin/jeprof.in#L4064-L4074
//
// However, this algorithm is actually wrong: you actually need to unbias each sample _before_ you add them together, rather
// than adding them together first and then unbiasing the average allocation size. But the heap profile format in released versions of jemalloc
// does not give us access to each individual allocation, so this is the best we can do (and `jeprof` does the same).
//
// It usually seems to be at least close enough to being correct to be useful, but could be very wrong if for the same stack, there is a
// very large amount of variance in the amount of bytes allocated (e.g., if there is one allocation of 8 MB and 1,000,000 of 8 bytes)
//
// In the latest unreleased jemalloc sources from github, the issue is worked around by unbiasing the numbers for each sampled allocation,
// and then fudging them to maintain compatibility with jeprof's logic. So, once those are released and we start using them,
// this will become even more correct.
//
// For more details, see this doc: https://github.com/jemalloc/jemalloc/pull/1902
//
// And this gitter conversation between me (Brennan Vincent) and David Goldblatt: https://gitter.im/jemalloc/jemalloc?at=5f31b673811d3571b3bb9b6b
let n_objs: f64 = str::parse(words[1].trim_end_matches(':'))?;
let bytes_in_sampled_objs: f64 = str::parse(words[2])?;
let ratio = (bytes_in_sampled_objs / n_objs) / sampling_rate;
let scale_factor = 1.0 / (1.0 - (-ratio).exp());
let weight = bytes_in_sampled_objs * scale_factor;
profile.push_stack(WeightedStack { addrs, weight }, None);
}
}
}
if cur_stack.is_some() {
bail!("Stack without corresponding weight!");
}
if let Some(mappings) = mappings {
for mapping in mappings {
profile.push_mapping(mapping.clone());
}
}
Ok(profile)
}