This commit replaces the "fuzzer" UI, previously accessed with the
`--fuzz` and `--port` flags, with a more interesting web UI which allows
more interactions with the Zig build system. Most notably, it allows
accessing the data emitted by a new "time report" system, which allows
users to see which parts of Zig programs take the longest to compile.
The option to expose the web UI is `--webui`. By default, it will listen
on `[::1]` on a random port, but any IPv6 or IPv4 address can be
specified with e.g. `--webui=[::1]:8000` or `--webui=127.0.0.1:8000`.
The options `--fuzz` and `--time-report` both imply `--webui` if not
given. Currently, `--webui` is incompatible with `--watch`; specifying
both will cause `zig build` to exit with a fatal error.
When the web UI is enabled, the build runner spawns the web server as
soon as the configure phase completes. The frontend code consists of one
HTML file, one JavaScript file, two CSS files, and a few Zig source
files which are built into a WASM blob on-demand -- this is all very
similar to the old fuzzer UI. Also inherited from the fuzzer UI is that
the build system communicates with web clients over a WebSocket
connection.
When the build finishes, if `--webui` was passed (i.e. if the web server
is running), the build runner does not terminate; it continues running
to serve web requests, allowing interactive control of the build system.
In the web interface is an overall "status" indicating whether a build
is currently running, and also a list of all steps in this build. There
are visual indicators (colors and spinners) for in-progress, succeeded,
and failed steps. There is a "Rebuild" button which will cause the build
system to reset the state of every step (note that this does not affect
caching) and evaluate the step graph again.
If `--time-report` is passed to `zig build`, a new section of the
interface becomes visible, which associates every build step with a
"time report". For most steps, this is just a simple "time taken" value.
However, for `Compile` steps, the compiler communicates with the build
system to provide it with much more interesting information: time taken
for various pipeline phases, with a per-declaration and per-file
breakdown, sorted by slowest declarations/files first. This feature is
still in its early stages: the data can be a little tricky to
understand, and there is no way to, for instance, sort by different
properties, or filter to certain files. However, it has already given us
some interesting statistics, and can be useful for spotting, for
instance, particularly complex and slow compile-time logic.
Additionally, if a compilation uses LLVM, its time report includes the
"LLVM pass timing" information, which was previously accessible with the
(now removed) `-ftime-report` compiler flag.
To make time reports more useful, ZIR and compilation caches are ignored
by the Zig compiler when they are enabled -- in other words, `Compile`
steps *always* run, even if their result should be cached. This means
that the flag can be used to analyze a project's compile time without
having to repeatedly clear cache directory, for instance. However, when
using `-fincremental`, updates other than the first will only show you
the statistics for what changed on that particular update. Notably, this
gives us a fairly nice way to see exactly which declarations were
re-analyzed by an incremental update.
If `--fuzz` is passed to `zig build`, another section of the web
interface becomes visible, this time exposing the fuzzer. This is quite
similar to the fuzzer UI this commit replaces, with only a few cosmetic
tweaks. The interface is closer than before to supporting multiple fuzz
steps at a time (in line with the overall strategy for this build UI,
the goal will be for all of the fuzz steps to be accessible in the same
interface), but still doesn't actually support it. The fuzzer UI looks
quite different under the hood: as a result, various bugs are fixed,
although other bugs remain. For instance, viewing the source code of any
file other than the root of the main module is completely broken (as on
master) due to some bogus file-to-module assignment logic in the fuzzer
UI.
Implementation notes:
* The `lib/build-web/` directory holds the client side of the web UI.
* The general server logic is in `std.Build.WebServer`.
* Fuzzing-specific logic is in `std.Build.Fuzz`.
* `std.Build.abi` is the new home of `std.Build.Fuzz.abi`, since it now
relates to the build system web UI in general.
* The build runner now has an **actual** general-purpose allocator,
because thanks to `--watch` and `--webui`, the process can be
arbitrarily long-lived. The gpa is `std.heap.DebugAllocator`, but the
arena remains backed by `std.heap.page_allocator` for efficiency. I
fixed several crashes caused by conflation of `gpa` and `arena` in the
build runner and `std.Build`, but there may still be some I have
missed.
* The I/O logic in `std.Build.WebServer` is pretty gnarly; there are a
*lot* of threads involved. I anticipate this situation improving
significantly once the `std.Io` interface (with concurrency support)
is introduced.
The implementation assumed that compilation units did not overlap, which
is not the case. The new implementation uses .debug_ranges to iterate
over the requested PCs.
This partially resolves#20990. The dump-cov tool is fixed but the same
fix needs to be applied to `std.Build.Fuzz.WebServer` (sorting the PC
list before passing it to be resolved by debug info).
I am observing LLVM emit multiple 8-bit counters for the same PC
addresses when enabling `-fsanitize-coverage=inline-8bit-counters`. This
seems like a bug in LLVM. I can't fathom why that would be desireable.
* Upgrade from u8 to usize element types.
- WebAssembly assumes u64. It should probably try to be target-aware
instead.
* Move the covered PC bits to after the header so it goes on the same
page with the other rapidly changing memory (the header stats).
depends on the semantics of accepted proposal #19755closes#20994
* libfuzzer: close file after mmap
* fuzzer/main.js: connect with EventSource and debug dump the messages.
currently this prints how many fuzzer runs have been attempted to
console.log.
* extract some `std.debug.Info` logic into `std.debug.Coverage`.
Prepares for consolidation across multiple different executables which
share source files, and makes it possible to send all the
PC/SourceLocation mapping data with 4 memcpy'd arrays.
* std.Build.Fuzz:
- spawn a thread to watch the message queue and signal event
subscribers.
- track coverage map data
- respond to /events URL with EventSource messages on a timer
* std.debug.Dwarf: add `sortCompileUnits` along with a field to track
the state for the purpose of assertions and correct API usage.
This makes batch lookups faster.
- in the future, findCompileUnit should be enhanced to rely on sorted
compile units as well.
* implement `std.debug.Dwarf.resolveSourceLocations` as well as
`std.debug.Info.resolveSourceLocations`. It's still pretty slow, since
it calls getLineNumberInfo for each array element, repeating a lot of
work unnecessarily.
* integrate these APIs with `std.Progress` to understand what is taking
so long.
The output I'm seeing from this tool shows a lot of missing source
locations. In particular, the main area of interest is missing for my
tokenizer fuzzing example.
with debug info resolved.
begin efforts of providing `std.debug.Info`, a cross-platform
abstraction for loading debug information into an in-memory format that
supports queries such as "what is the source location of this virtual
memory address?"
Unlike `std.debug.SelfInfo`, this API does not assume the debug
information in question happens to match the host CPU architecture, OS,
or other target properties.
