Document -Zinstrument-coverage #78616

richkadel · 2020-10-31T23:42:34Z

r? @tmandry
FYI @wesleywiser

Here is my proposed document for LLVM source-based code coverage.

I based it on the profile.md page, in the same directory, and on the Clang guide for LLVM source-based coverage.

Julian-Wollersberger

Nice description!

cc #34701 and rust-lang/compiler-team#278

Julian-Wollersberger · 2020-11-01T21:59:23Z

src/doc/unstable-book/src/compiler-flags/source-based-code-coverage.md

+First, edit the `config.toml` file, and find the `profiler` feature entry. It may be commented out:
+
+```toml
+# Build the profiler runtime (required when compiling with options that depend
+# on this runtime, such as `-C profile-generate` or `-Z instrument-coverage`).
+#profiler = false
+```
+
+Uncomment the feature entry and set it to `true`:
+
+```toml
+profiler = true


Suggested change

First, edit the `config.toml` file, and find the `profiler` feature entry. It may be commented out:

```toml

# Build the profiler runtime (required when compiling with options that depend

# on this runtime, such as `-C profile-generate` or `-Z instrument-coverage`).

#profiler = false

```

Uncomment the feature entry and set it to `true`:

```toml

profiler = true

First, edit the `config.toml` file, and find the `profiler` feature entry. Uncomment it and set it to `true`:

```toml

# Build the profiler runtime (required when compiling with options that depend

# on this runtime, such as `-C profile-generate` or `-Z instrument-coverage`).

profiler = true

The phrasing here is a bit verbose.

Julian-Wollersberger · 2020-11-01T22:13:12Z

src/doc/unstable-book/src/compiler-flags/source-based-code-coverage.md

+After running this program, a new file, `default.profraw`, should be in the current working directory:
+
+```shell
+$ ls -l default.profraw
+```
+```text
+-rw-r--r-- 1 user group 3.3M Oct 31 12:31 default.profraw
+```


I'd remove the ls example here. Again, to verbose for my taste.

richkadel · 2020-11-02T06:20:41Z

cc #34701 and rust-lang/compiler-team#278

tmandry

@bors delegate+

r=me after comments

tmandry · 2020-11-02T18:08:18Z

src/doc/unstable-book/src/compiler-flags/source-based-code-coverage.md

+
+Then rebuild the Rust compiler (see [rustc-dev-guide-how-to-build-and-run]).
+
+### Building the demangler


We could also point to rustfilt, which can be installed with cargo and doesn't require a rust checkout.

I hadn't heard about rustfilt before! That's a great option as well.

tmandry · 2020-11-02T18:09:07Z

src/doc/unstable-book/src/compiler-flags/source-based-code-coverage.md

+
+## Enable coverage profiling in the Rust compiler
+
+*IMPORTANT:* Rust's coverage profiling features may not be enabled, by default. To enable them, you may need to build a version of the Rust compiler with the `profiler` feature enabled.


Many of the tier 1 distributions ship with this enabled (grep for --enable-profiler)

As discussed offline, I now discuss using nightly as an option

tmandry · 2020-11-02T18:13:28Z

src/doc/unstable-book/src/compiler-flags/source-based-code-coverage.md

+Raw profiles have to be indexed before they can be used to generate coverage reports. This is done using [`llvm-profdata merge`] (which can combine multiple raw profiles and index them at the same time):
+
+```shell
+$ $HOME/rust/build/x86_64-unknown-linux-gnu/llvm/bin/llvm-profdata merge \


Maybe we can show / mention doing it with system LLVM instead of requiring a rust build?

(Unless it has to match the exact LLVM version?)

tmandry · 2020-11-02T18:19:41Z

@bors delegate+

bors · 2020-11-02T18:19:44Z

✌️ @richkadel can now approve this pull request

richkadel · 2020-11-02T20:09:28Z

@bors rollup=always r=tmandry

bors · 2020-11-02T20:09:30Z

📌 Commit 6d94911 has been approved by tmandry

…r=tmandry Document -Zinstrument-coverage r? `@tmandry` FYI `@wesleywiser` Here is my proposed document for LLVM source-based code coverage. I based it on the `profile.md` page, in the same directory, and on the Clang guide for LLVM source-based coverage.

Rollup of 8 pull requests Successful merges: - rust-lang#78376 (Treat trailing semicolon as a statement in macro call) - rust-lang#78400 (Fix unindent in doc comments) - rust-lang#78575 (Add a test for compiletest rustc-env & unset-rustc-env directives) - rust-lang#78616 (Document -Zinstrument-coverage) - rust-lang#78663 (Fix ICE when a future-incompat-report has its command-line level capped) - rust-lang#78664 (Fix intrinsic size_of stable link) - rust-lang#78668 (inliner: Remove redundant loop) - rust-lang#78676 (add mipsel-unknown-none target) Failed merges: r? `@ghost` `@rustbot` modify labels: rollup

rust-highfive assigned tmandry Oct 31, 2020

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richkadel force-pushed the unstable-book-instr-cov branch 3 times, most recently from 016ca3d to 179ac85 Compare November 1, 2020 00:31

Julian-Wollersberger reviewed Nov 1, 2020

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Document -Zinstrument-coverage

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richkadel force-pushed the unstable-book-instr-cov branch from 179ac85 to a8dfb26 Compare November 2, 2020 04:13

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richkadel force-pushed the unstable-book-instr-cov branch from f2fe33b to 6d94911 Compare November 2, 2020 20:06

bors added S-waiting-on-bors Status: Waiting on bors to run and complete tests. Bors will change the label on completion. and removed S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. labels Nov 2, 2020

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Rollup of 9 pull requests #78693

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Rollup of 8 pull requests #78697

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bors merged commit 416dd67 into rust-lang:master Nov 3, 2020

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Document -Zinstrument-coverage #78616

Document -Zinstrument-coverage #78616

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		Then rebuild the Rust compiler (see [rustc-dev-guide-how-to-build-and-run]).

		### Building the demangler


		## Enable coverage profiling in the Rust compiler

		IMPORTANT: Rust's coverage profiling features may not be enabled, by default. To enable them, you may need to build a version of the Rust compiler with the `profiler` feature enabled.

Document -Zinstrument-coverage #78616

Document -Zinstrument-coverage #78616

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