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Providing a hermetic C/C++ toolchain #20

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aherrmann opened this issue Oct 5, 2022 · 0 comments
Closed

Providing a hermetic C/C++ toolchain #20

aherrmann opened this issue Oct 5, 2022 · 0 comments

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@aherrmann
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A self-contained C/C++ toolchain that doesn't assume pre-installed components on the system ensures a consistent build behavior across environments (CI or different developer machines). Traditionally, obtaining a self-contained C/C++ compiler distribution has been quite difficult. The closest commonly used one in the Bazel ecosystem is the LLVM toolchain created by Grail, however, this one still assumes a global or separately provided sysroot. An easier to use alternative is zig cc built on top of clang and already used for Bazel in bazel-zig-cc, which also has builtin support for cross-compilation.

Similar to #19
@aherrmann aherrmann mentioned this issue Oct 7, 2022
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facebook-github-bot pushed a commit that referenced this issue Oct 10, 2022
@aherrmann @facebook-github-bot
Create self-contained cxx_zig_toolchain (#22)
b8e5cf0 
Summary:
Closes #20

Adds `prelude//toolchains/cxx/zig` with a C/C++ toolchain based on `zig cc`.
The doc-string of the added module contains a description and examples
configurations.

Also adds an example to the repository that builds a C++ library and a binary
depending on that library using this toolchain.

Note, for that example to work in the open source buck2 tree the following additional patch needs to be applied:
```diff
 diff --git a/.buckconfig b/.buckconfig
deleted file mode 100644
index c32af92..0000000
 --- a/.buckconfig
+++ /dev/null
@@ -1,19 +0,0 @@
-[repositories]
-root = .
-prelude = prelude
-ovr_config = prelude
-shim = shim
-toolchains = shim
-fbcode = shim
-fbcode_macros = shim
-fbsource = shim
-buck = shim
-
-[buildfile]
-name = TARGETS
-
-[build]
-execution_platforms = ovr_config//platforms:default
-
-[parser]
-target_platform_detector_spec = target://...->ovr_config//platforms:default
 diff --git a/prelude/cxx/tools/TARGETS.v2 b/prelude/cxx/tools/TARGETS.v2
index 2030d2f..5db1689 100644
 --- a/prelude/cxx/tools/TARGETS.v2
+++ b/prelude/cxx/tools/TARGETS.v2
@@ -1,4 +1,3 @@
-load("fbcode_macros//build_defs/lib:python_common.bzl", "get_ldflags", "get_strip_mode")
 load(":defs.bzl", "cxx_hacks", "omnibus_environment")

 prelude = native
@@ -538,7 +537,7 @@ omnibus_environment(
     # We override the binary-level ldflags with library level ldfalgs for
     # shared roots. We include 2 important things: stripping binaries, and not
     # discarding GPU code.
-    shared_root_ld_flags = get_ldflags("", "", "omnibus_root", get_strip_mode("", ""), "") + [
+    shared_root_ld_flags = [
         "-Wl,--no-discard-section=.nv_fatbin",
         "-Wl,--no-discard-section=.nvFatBinSegment",
         # Reorder nv_fatbin after the bss section to avoid overflow
```

Pull Request resolved: #22

Reviewed By: arlyon

Differential Revision: D40179209

Pulled By: arlyon

fbshipit-source-id: d334f2ad4563281f78ba3f479b8defd09616cabf
facebook-github-bot pushed a commit that referenced this issue Feb 15, 2024
@JakobDegen @facebook-github-bot
dice: Remove some logging
18654c7 
Summary:
The stack around D42099161 introduced the ability to dynamically set the log level via a debug-command. This requires using `tracing_subscriber::reload::Layer`. The implementation of that machinery is backed by a `RwLock` [here](https://fburl.com/code/4xv0ihpn). This `RwLock` is read locked once on every single `#[instrumentation]` call to check whether the instrumentation is active or not.

On top of that, something in our fbsource third-party config enables the `parking_lot` feature of `tracing_subscriber`. This means that this is a `parking_lot::RwLock`, not a `std::sync::RwLock`, which is bad because it's well known that parking lot has problems with excessive spinning.

What all that adds up to is that when you put `#[instrument]` on a super hot function in dice, you get dozens of threads that are all simultaneously doing this:

```
  thread #23, name = 'buck2-rt', stop reason = signal SIGSTOP
    frame #0: 0x000000000c94a1fa buck2`<parking_lot::raw_rwlock::RawRwLock>::lock_shared_slow + 122
    frame #1: 0x0000000007a80b54 buck2`<tracing_subscriber::layer::layered::Layered<tracing_subscriber::reload::Layer<tracing_subscriber::filter::layer_filters::Filtered<tracing_subscriber::fmt::fmt_layer::Layer<tracing_subscriber::registry::sharded::Registry, tracing_subscriber::fmt::format::DefaultFields, tracing_subscriber::fmt::format::Format, std::io::stdio::stderr>, tracing_subscriber::filter::env::EnvFilter, tracing_subscriber::registry::sharded::Registry>, tracing_subscriber::registry::sharded::Registry>, tracing_subscriber::registry::sharded::Registry> as tracing_core::subscriber::Subscriber>::enabled + 292
    frame #2: 0x000000000a172d77 buck2`<dice::legacy::incremental::dep_trackers::internals::Dep<dice::legacy::key::StoragePropertiesForKey<buck2_build_api::actions::calculation::BuildKey>> as dice::legacy::incremental::graph::dependencies::Dependency>::recompute::{closure#0} + 183
    frame #3: 0x000000000a03606c buck2`<futures_util::stream::futures_unordered::FuturesUnordered<core::pin::Pin<alloc::boxed::Box<dyn core::future::future::Future<Output = core::result::Result<(alloc::boxed::Box<dyn dice::legacy::incremental::graph::dependencies::ComputedDependency>, alloc::sync::Arc<dyn dice::legacy::incremental::graph::GraphNodeDyn>), dice::api::error::DiceError>> + core::marker::Send>>> as futures_util::stream::stream::StreamExt>::poll_next_unpin + 444
    frame #4: 0x0000000009fc4755 buck2`<dice::legacy::incremental::IncrementalEngine<dice::legacy::key::StoragePropertiesForKey<buck2_build_api::actions::calculation::BuildKey>>>::compute_whether_dependencies_changed::{closure#0} (.llvm.4229350879637282184) + 1733
    frame #5: 0x0000000009ef30d4 buck2`<dice::legacy::incremental::IncrementalEngine<dice::legacy::key::StoragePropertiesForKey<buck2_build_api::actions::calculation::BuildKey>>>::compute_whether_versioned_dependencies_changed::{closure#0}::{closure#0} + 228
    frame #6: 0x0000000009f194ec buck2`<buck2_futures::cancellable_future::CancellableFuture<<dice::legacy::incremental::IncrementalEngine<dice::legacy::key::StoragePropertiesForKey<buck2_build_api::actions::calculation::BuildKey>>>::new_dice_task::{closure#0}> as core::future::future::Future>::poll (.llvm.11181184606289051452) + 3500
    frame #7: 0x0000000009f04bbf buck2`<futures_util::future::future::map::Map<buck2_futures::cancellable_future::CancellableFuture<<dice::legacy::incremental::IncrementalEngine<dice::legacy::key::StoragePropertiesForKey<buck2_build_api::actions::calculation::BuildKey>>>::new_dice_task::{closure#0}>, buck2_futures::spawn::spawn_inner<<dice::legacy::incremental::IncrementalEngine<dice::legacy::key::StoragePropertiesForKey<buck2_build_api::actions::calculation::BuildKey>>>::new_dice_task::{closure#0}, dice::api::user_data::UserComputationData, futures_util::future::ready::Ready<()>>::{closure#0}> as core::future::future::Future>::poll + 31
    frame #8: 0x0000000009ff0339 buck2`<futures_util::future::future::flatten::Flatten<futures_util::future::future::Map<futures_util::future::ready::Ready<()>, buck2_futures::spawn::spawn_inner<<dice::legacy::incremental::IncrementalEngine<dice::legacy::key::StoragePropertiesForKey<buck2_build_api::actions::calculation::BuildKey>>>::new_dice_task::{closure#0}, dice::api::user_data::UserComputationData, futures_util::future::ready::Ready<()>>::{closure#1}>, <futures_util::future::future::Map<futures_util::future::ready::Ready<()>, buck2_futures::spawn::spawn_inner<<dice::legacy::incremental::IncrementalEngine<dice::legacy::key::StoragePropertiesForKey<buck2_build_api::actions::calculation::BuildKey>>>::new_dice_task::{closure#0}, dice::api::user_data::UserComputationData, futures_util::future::ready::Ready<()>>::{closure#1}> as core::future::future::Future>::Output> as core::future::future::Future>::poll + 201
    frame #9: 0x00000000093f9f22 buck2`<tokio::task::task_local::TaskLocalFuture<buck2_events::dispatch::EventDispatcher, core::pin::Pin<alloc::boxed::Box<dyn core::future::future::Future<Output = alloc::boxed::Box<dyn core::any::Any + core::marker::Send>> + core::marker::Send>>> as core::future::future::Future>::poll + 130
    frame #10: 0x000000000939fdcb buck2`<tracing::instrument::Instrumented<<buck2_build_api::spawner::BuckSpawner as buck2_futures::spawner::Spawner<dice::api::user_data::UserComputationData>>::spawn::{closure#0}> as core::future::future::Future>::poll + 139
    frame #11: 0x00000000091ca5a9 buck2`<tokio::runtime::task::core::Core<tracing::instrument::Instrumented<<buck2_build_api::spawner::BuckSpawner as buck2_futures::spawner::Spawner<dice::api::user_data::UserComputationData>>::spawn::{closure#0}>, alloc::sync::Arc<tokio::runtime::scheduler::multi_thread::handle::Handle>>>::poll + 169
    frame #12: 0x00000000091c1b22 buck2`<tokio::runtime::task::harness::Harness<tracing::instrument::Instrumented<<buck2_build_api::spawner::BuckSpawner as buck2_futures::spawner::Spawner<dice::api::user_data::UserComputationData>>::spawn::{closure#0}>, alloc::sync::Arc<tokio::runtime::scheduler::multi_thread::handle::Handle>>>::poll + 146
    frame #13: 0x000000000c920f6f buck2`<tokio::runtime::scheduler::multi_thread::worker::Context>::run_task + 895
    frame #14: 0x000000000c91f847 buck2`<tokio::runtime::scheduler::multi_thread::worker::Context>::run + 2103
    frame #15: 0x000000000c932264 buck2`<tokio::runtime::context::scoped::Scoped<tokio::runtime::scheduler::Context>>::set::<tokio::runtime::scheduler::multi_thread::worker::run::{closure#0}::{closure#0}, ()> + 52
    frame #16: 0x000000000c932169 buck2`tokio::runtime::context::runtime::enter_runtime::<tokio::runtime::scheduler::multi_thread::worker::run::{closure#0}, ()> + 441
    frame #17: 0x000000000c91efa6 buck2`tokio::runtime::scheduler::multi_thread::worker::run + 70
    frame #18: 0x000000000c906a50 buck2`<tracing::instrument::Instrumented<tokio::runtime::blocking::task::BlockingTask<<tokio::runtime::scheduler::multi_thread::worker::Launch>::launch::{closure#0}>> as core::future::future::Future>::poll + 160
    frame #19: 0x000000000c8f8af9 buck2`<tokio::loom::std::unsafe_cell::UnsafeCell<tokio::runtime::task::core::Stage<tracing::instrument::Instrumented<tokio::runtime::blocking::task::BlockingTask<<tokio::runtime::scheduler::multi_thread::worker::Launch>::launch::{closure#0}>>>>>::with_mut::<core::task::poll::Poll<()>, <tokio::runtime::task::core::Core<tracing::instrument::Instrumented<tokio::runtime::blocking::task::BlockingTask<<tokio::runtime::scheduler::multi_thread::worker::Launch>::launch::{closure#0}>>, tokio::runtime::blocking::schedule::BlockingSchedule>>::poll::{closure#0}> + 153
    frame #20: 0x000000000c90166b buck2`<tokio::runtime::task::core::Core<tracing::instrument::Instrumented<tokio::runtime::blocking::task::BlockingTask<<tokio::runtime::scheduler::multi_thread::worker::Launch>::launch::{closure#0}>>, tokio::runtime::blocking::schedule::BlockingSchedule>>::poll + 43
    frame #21: 0x000000000c90d9b8 buck2`<tokio::runtime::task::harness::Harness<tracing::instrument::Instrumented<tokio::runtime::blocking::task::BlockingTask<<tokio::runtime::scheduler::multi_thread::worker::Launch>::launch::{closure#0}>>, tokio::runtime::blocking::schedule::BlockingSchedule>>::poll + 152
    frame #22: 0x000000000c90b848 buck2`<tokio::runtime::blocking::pool::Inner>::run + 216
    frame #23: 0x000000000c9002ab buck2`std::sys_common::backtrace::__rust_begin_short_backtrace::<<tokio::runtime::blocking::pool::Spawner>::spawn_thread::{closure#0}, ()> + 187
    frame #24: 0x000000000c90042e buck2`<<std::thread::Builder>::spawn_unchecked_<<tokio::runtime::blocking::pool::Spawner>::spawn_thread::{closure#0}, ()>::{closure#1} as core::ops::function::FnOnce<()>>::call_once::{shim:vtable#0} + 158
    frame #25: 0x000000000757e4b5 buck2`std::sys::unix::thread::Thread::new::thread_start::h618b0b8e7bda0b2b + 37
    frame #26: 0x00007f2ba1e9abaf
```

This hit an open source user super hard over in #555 .

This diff approaches this issue by putting all the `#[instrument]`s in dice behind `#[cfg(debug_assertions)]`. This allows them to still be used in debug mode, but keeps them out of any hot paths. I do not have numbers to show that most of these matter. The only one I know matters for sure is `recompute`.

Alternatives are to either try and tailor this to the callsites we know are hot (that sounds error prone) or to revert the stack that inadvertently introduced the RwLock. Even if we did that though, it's probably still safer to keep `#[instrument]` out of super hot paths like this.

Reviewed By: stepancheg

Differential Revision: D53744041

fbshipit-source-id: 85bce9af2fec8ad1d50adc241d3b8e2bfc5cec87
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Create self-contained cxx_zig_toolchain facebook/buck2
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@aherrmann