-Zprofile broken in nightly?

[mssun]

I am using -Zprofile to use gcov. However, the results are corrupted.

Here are my info.

$ cargo -V
cargo 1.26.0-nightly (008c36908 2018-04-13)
$ rustc -V
rustc 1.27.0-nightly (ac3c2288f 2018-04-18)

Reproduce the issue:

$ cargo new hello_world --bin
$ cargo rustc --bins -- -Zprofile -Copt-level=1 -Clink-dead-code -Ccodegen-units=1 -Zno-landing-pads
$ ./target/debug/hello_world
./target/debug/hello_world
Hello, world!
profiling: /hello_world/target/debug/deps/hello_world-b633c1f029999720.gcda: cannot merge previous GCDA file: corrupt arc tag (0x66353136)
profiling: /hello_world/target/debug/deps/hello_world-b633c1f029999720.gcda: cannot merge previous run count: corrupt object tag (0x37633437)
profiling: /hello_world/target/debug/deps/hello_world-b633c1f029999720.gcda: cannot merge previous GCDA file: corrupt arc tag (0x66353136)
profiling: /hello_world/target/debug/deps/hello_world-b633c1f029999720.gcda: cannot merge previous GCDA file: corrupt arc tag (0x63626564)
profiling: /hello_world/target/debug/deps/hello_world-b633c1f029999720.gcda: cannot merge previous run count: corrupt object tag (0x00456238)
profiling: /hello_world/target/debug/deps/hello_world-b633c1f029999720.gcda: cannot merge previous GCDA file: corrupt arc tag (0x38327472)
profiling: /hello_world/target/debug/deps/hello_world-b633c1f029999720.gcda: cannot merge previous GCDA file: corrupt arc tag (0x00000000)
profiling: /hello_world/target/debug/deps/hello_world-b633c1f029999720.gcda: cannot merge previous run count: corrupt object tag (0xa3000000)
profiling: /hello_world/target/debug/deps/hello_world-b633c1f029999720.gcda: cannot merge previous GCDA file: corrupt arc tag (0x246e6f69)
profiling: /hello_world/target/debug/deps/hello_world-b633c1f029999720.gcda: cannot merge previous run count: corrupt object tag (0x36245447)
profiling: /hello_world/target/debug/deps/hello_world-b633c1f029999720.gcda: cannot merge previous GCDA file: corrupt arc tag (0x36626331)
profiling: /hello_world/target/debug/deps/hello_world-b633c1f029999720.gcda: cannot merge previous run count: corrupt object tag (0x00004530)

It works when using older version:

$ rustup override set nightly-2017-06-28

I don't know if this issue related with kennytm/cov#18

Also: ping #42524

[marco-c]

It would be great if we could bisect this, to know what caused the regression.

[mssun]

Thanks. It still breaks on the latest nightly.

$ rustc -V
rustc 1.28.0-nightly (4a9c58c6b 2018-06-05)
$ cargo -V
cargo 1.28.0-nightly (c3b09c968 2018-05-27)

This feature is really important to get a proper code coverage profile.

[marco-c]

I'm trying to bisect manually.
For now:
2018-01-01 is broken.
2017-12-15 is working.

[marco-c]

2017-12-24 is working. 2017-12-25 is broken.
Here are the commits landed between those two days: https://github.com/rust-lang/rust/compare/master@%7B2017-12-24%7D...master@%7B2017-12-25%7D.

[marco-c]

I guess we should have added parsing of gcda as part of this test: https://github.com/rust-lang/rust/blob/master/src/test/run-make-fulldeps/profile/Makefile.

[marco-c]

@alexcrichton is the range from #50203 (comment) correct? I guess there's a precise way to tell what commit a given Nightly build correspons to?

[kennytm]

C:\> rustc +nightly-2017-12-24 -vV
rustc 1.24.0-nightly (169929308 2017-12-23)
binary: rustc
commit-hash: 16992930835ce3376a4aaed42307726e1fc78e45
commit-date: 2017-12-23
host: x86_64-pc-windows-msvc
release: 1.24.0-nightly
LLVM version: 4.0

C:\> rustc +nightly-2017-12-25 -vV
rustc 1.24.0-nightly (c284f8807 2017-12-24)
binary: rustc
commit-hash: c284f8807eb3a1d728242bb6a767b0306d6f6bd5
commit-date: 2017-12-24
host: x86_64-pc-windows-msvc
release: 1.24.0-nightly
LLVM version: 4.0

The regression happens between 1699293...c284f88

PRs in this range:

• incr.comp.: Cache check_match and use ensure() for coherence-related queries. #46881 (incr.comp.: Cache check_match and use ensure() for coherence-related queries.)
• Prevent unwinding past FFI boundaries #46833 (Prevent unwinding past FFI boundaries)
• Add a feature gate for nested uses of impl Trait #46888 (Add a feature gate for nested uses of impl Trait)
• Only mark unions as uninhabited if all of their fields are uninhabited #46859 (Only mark unions as uninhabited if all of their fields are uninhabited)
• Const-eval array lengths in rustdoc. #46894 (Const-eval array lengths in rustdoc.)
• fix debuginfo scoping of let-statements #46896 (fix debuginfo scoping of let-statements)
• Update Cargo and its dependencies #46630 (Update Cargo and its dependencies)
• Capture Command environment at spawn #46789 (Capture Command environment at spawn)

Fast PR-by-PR bisection is impossible at this point since the artifacts have been deleted.

[marco-c]

Thanks @kennytm. I've tested with 4910ed2 and it is working. So the regression is between 4910ed2 and c284f88.

[kennytm]

It is caused by incremental compilation.

~:45$ rustc --crate-name hello_world src/main.rs --crate-type bin --emit=link -C debuginfo=2 -Zprofile -Copt-level=1 -Clink-dead-code -Ccodegen-units=1 -Zno-landing-pads -C metadata=e6641c514587dc22 -C extra-filename=-e6641c514587dc22 --out-dir ~/hello_world/target/debug/deps 

~:46$ ./target/debug/deps/hello_world-e6641c514587dc22
Hello, world!

~:47$ rustc --crate-name hello_world src/main.rs --crate-type bin --emit=link -C debuginfo=2 -Zprofile -Copt-level=1 -Clink-dead-code -Ccodegen-units=1 -Zno-landing-pads -C metadata=e6641c514587dc22 -C extra-filename=-e6641c514587dc22 --out-dir ~/hello_world/target/debug/deps -C incremental=~/hello_world/target/debug/incremental

~:48$ ./target/debug/deps/hello_world-e6641c514587dc22
Hello, world!
profiling: ~/hello_world/target/debug/deps/hello_world-e6641c514587dc22.gcda: cannot merge previous GCDA file: corrupt arc tag (0x00000001)
profiling: ~/hello_world/target/debug/deps/hello_world-e6641c514587dc22.gcda: cannot merge previous GCDA file: corrupt arc tag (0x24246437)
profiling: ~/hello_world/target/debug/deps/hello_world-e6641c514587dc22.gcda: cannot merge previous run count: corrupt object tag (0x24643775)
profiling: ~/hello_world/target/debug/deps/hello_world-e6641c514587dc22.gcda: cannot merge previous GCDA file: corrupt arc tag (0x39383038)
profiling: ~/hello_world/target/debug/deps/hello_world-e6641c514587dc22.gcda: cannot merge previous run count: corrupt object tag (0x32626265)
profiling: ~/hello_world/target/debug/deps/hello_world-e6641c514587dc22.gcda: cannot merge previous GCDA file: corrupt arc tag (0x39383038)
profiling: ~/hello_world/target/debug/deps/hello_world-e6641c514587dc22.gcda: cannot merge previous GCDA file: corrupt arc tag (0x00000000)
profiling: ~/hello_world/target/debug/deps/hello_world-e6641c514587dc22.gcda: cannot merge previous run count: corrupt object tag (0x62333333)
profiling: ~/hello_world/target/debug/deps/hello_world-e6641c514587dc22.gcda: cannot merge previous GCDA file: corrupt arc tag (0x38327472)
profiling: ~/hello_world/target/debug/deps/hello_world-e6641c514587dc22.gcda: cannot merge previous GCDA file: corrupt arc tag (0x34737973)
profiling: ~/hello_world/target/debug/deps/hello_world-e6641c514587dc22.gcda: cannot merge previous run count: corrupt object tag (0x78696e75)
profiling: ~/hello_world/target/debug/deps/hello_world-e6641c514587dc22.gcda: cannot merge previous GCDA file: corrupt arc tag (0x246e6f69)
profiling: ~/hello_world/target/debug/deps/hello_world-e6641c514587dc22.gcda: cannot merge previous run count: corrupt object tag (0x36245447)
profiling: ~/hello_world/target/debug/deps/hello_world-e6641c514587dc22.gcda: cannot merge previous GCDA file: corrupt arc tag (0x38306266)
profiling: ~/hello_world/target/debug/deps/hello_world-e6641c514587dc22.gcda: cannot merge previous run count: corrupt object tag (0x00004538)