Make __libcpp_verbose_abort() noexcept like std::terminate()

[dougsonos]

Make __libcpp_verbose_abort() noexcept (it is already noreturn), to match std::terminate(). Clang's function effect analysis can use this to ignore such functions as being beyond its scope. (See #99656)

[llvmbot]

@llvm/pr-subscribers-libcxx

Author: Doug Wyatt (dougsonos)

Changes

Make __libcpp_verbose_abort() noexcept (it is already noreturn), to match std::terminate(). Clang's function effect analysis can use this to ignore such functions as being beyond its scope. (See #99656)

---

Full diff: https://github.com/llvm/llvm-project/pull/109151.diff

1 Files Affected:

• (modified) libcxx/include/__verbose_abort (+2-1)

diff --git a/libcxx/include/__verbose_abort b/libcxx/include/__verbose_abort
index 244278aec652d2..45a0add493c17d 100644
--- a/libcxx/include/__verbose_abort
+++ b/libcxx/include/__verbose_abort
@@ -21,7 +21,8 @@ _LIBCPP_BEGIN_NAMESPACE_STD
 // This function should never be called directly from the code -- it should only be called through
 // the _LIBCPP_VERBOSE_ABORT macro.
 [[__noreturn__]] _LIBCPP_AVAILABILITY_VERBOSE_ABORT _LIBCPP_OVERRIDABLE_FUNC_VIS
-_LIBCPP_ATTRIBUTE_FORMAT(__printf__, 1, 2) void __libcpp_verbose_abort(const char* __format, ...);
+_LIBCPP_ATTRIBUTE_FORMAT(__printf__, 1, 2) void __libcpp_verbose_abort(const char* __format, ...)
+_NOEXCEPT;
 
 // _LIBCPP_VERBOSE_ABORT(format, args...)
 //

[github-actions]

✅ With the latest revision this PR passed the C/C++ code formatter.

[dougsonos]

Oops, I forgot to make the implementation noexcept too. This highlights that the question here is whether changing this interface to noexcept is going to break anything...

[ldionne]

This makes sense to me, however this is technically a breaking change because in the past we have advertised __libcpp_verbose_abort as being overridable (that's why it was a weak def).

We'd also want to add a release note for this change in libcxx/docs/ReleaseNotes/20.rst, probably under Deprecations and Removals.

Pinging @llvm/libcxx-vendors for awareness.

[dougsonos]

Any pointers on what's going on with the test builds? I click Details and just see "job failed".

[ldionne]

Any pointers on what's going on with the test builds? I click Details and just see "job failed".

Our CI is currently in a really bad state. Workers are failing to connect. This has been going on for a few days and we're trying to resolve the issue. Sorry for the inconvenience.

[ldionne]

Please rebase onto main to re-trigger CI. The CI instability should be resolved now.

[dougsonos]

I should have trusted the CI and seen this error!

# | /home/runner/_work/llvm-project/llvm-project/libcxx/test/libcxx/assertions/customize_verbose_abort.link-time.pass.cpp:18:52: error: expected function body after function declarator
# |    18 | void std::__libcpp_verbose_abort(char const*, ...) noexcept { std::exit(EXIT_SUCCESS); }
# |       |                                                    ^
# | 1 error generated.

This is in a C++03 test.

[dougsonos]

Ping

[BwL1289]

@dougsonos this breaks flang compilation because flang overrides this symbol and doesn't use noexcept attribute

[dougsonos]

@dougsonos this breaks flang compilation because flang overrides this symbol and doesn't use noexcept attribute

Apologies. Can we fix flang to match?

[ldionne]

@dougsonos this breaks flang compilation because flang overrides this symbol and doesn't use noexcept attribute

In fact, we want to move away from supporting overriding that function. The way of customizing the assertion handler is when configuring the library, as explained here: https://libcxx.llvm.org/Hardening.html#overriding-the-assertion-failure-handler

[mstorsjo]

@dougsonos this breaks flang compilation because flang overrides this symbol and doesn't use noexcept attribute

In fact, we want to move away from supporting overriding that function. The way of customizing the assertion handler is when configuring the library, as explained here: https://libcxx.llvm.org/Hardening.html#overriding-the-assertion-failure-handler

@ldionne - The issue here from the Flang perspective, is not that flang want to override the function, they don't really care. The thing is that Flang uses some classes from the C++ standard library (from std::variant iirc) but don't want to link against the C++ standard library. When using the libc++ implementation of std::variant, they end up with undefined references to std::__libcpp_verbose_abort unless they actually override/provide it themselves.

[ldionne]

Moving the discussion to #113059 (comment) to centralize things.

[Caslyn]

Hi @dougsonos @ldionne (sorry, typo on the author name)

Unfortunately this is breaking when trying to build Fuchsia with a clang version that includes this change. Here is a link to the build failure we're seeing:

https://luci-milo.appspot.com/ui/p/fuchsia/builders/ci/clang_toolchain.ci.core.arm64-debug/b8733819071213133329/overview

There are places in the Fuchsia checkout that provide their own definitions of this function:

https://cs.opensource.google/search?q=__libcpp_verbose_abort

Can you make this backwards compatible to enable us to transition to the noexcept version of this function?