[libc][stdlib] initial support for __cxa_finalize

[nickdesaulniers]

I'm trying to break up the pieces of supporting __cxa_finalize into smaller
commits. Provide this symbol first, and make use of it from exit.

Next will be to store __dso_handle, then finally to only run callbacks that
were registered from a specific dso.

Link: #85651
Link: https://itanium-cxx-abi.github.io/cxx-abi/abi.html#dso-dtor

[llvmbot]

@llvm/pr-subscribers-libc

Author: Nick Desaulniers (nickdesaulniers)

Changes

I'm trying to break up the pieces of supporting __cxa_finalize into smaller
commits. Provide this symbol first, and make use of it from exit.

Next will be to store __dso_handle, then finally to only run callbacks that
were registered from a specific dso.

Link: #85651
Link: https://itanium-cxx-abi.github.io/cxx-abi/abi.html#dso-dtor

---

Full diff: https://github.com/llvm/llvm-project/pull/85865.diff

2 Files Affected:

• (modified) libc/src/stdlib/atexit.cpp (+19-12)
• (modified) libc/src/stdlib/exit.cpp (+3-5)

diff --git a/libc/src/stdlib/atexit.cpp b/libc/src/stdlib/atexit.cpp index 741ea4f25103ac..fa072b2fdf8d09 100644 --- a/libc/src/stdlib/atexit.cpp +++ b/libc/src/stdlib/atexit.cpp @@ -55,14 +55,10 @@ void stdc_at_exit_func(void *payload) { reinterpret_cast<StdCAtExitCallback *>(payload)(); } -} // namespace - -namespace internal { - void call_exit_callbacks() { handler_list_mtx.lock(); while (!exit_callbacks.empty()) { - auto unit = exit_callbacks.back(); + AtExitUnit &unit = exit_callbacks.back(); exit_callbacks.pop_back(); handler_list_mtx.unlock(); unit.callback(unit.payload); @@ -71,20 +67,31 @@ void call_exit_callbacks() { ExitCallbackList::destroy(&exit_callbacks); } -} // namespace internal - -static int add_atexit_unit(const AtExitUnit &unit) { +int add_atexit_unit(const AtExitUnit &unit) { MutexLock lock(&handler_list_mtx); - if (!exit_callbacks.push_back(unit)) - return -1; - return 0; + if (exit_callbacks.push_back(unit)) + return 0; + return -1; } +} // namespace + +extern "C" { + // TODO: Handle the last dso handle argument. -extern "C" int __cxa_atexit(AtExitCallback *callback, void *payload, void *) { +int __cxa_atexit(AtExitCallback *callback, void *payload, void *) { return add_atexit_unit({callback, payload}); } +// TODO: Handle the dso handle argument. call_exit_callbacks should only invoke +// the callbacks from this DSO. Requires adding support for __dso_handle. +void __cxa_finalize(void *dso) { + if (!dso) + call_exit_callbacks(); +} + +} // extern "C" + LLVM_LIBC_FUNCTION(int, atexit, (StdCAtExitCallback * callback)) { return add_atexit_unit( {&stdc_at_exit_func, reinterpret_cast<void *>(callback)}); diff --git a/libc/src/stdlib/exit.cpp b/libc/src/stdlib/exit.cpp index cc5ae6648d11f2..e754b34e46985a 100644 --- a/libc/src/stdlib/exit.cpp +++ b/libc/src/stdlib/exit.cpp @@ -10,14 +10,12 @@ #include "src/__support/OSUtil/quick_exit.h" #include "src/__support/common.h" -namespace LIBC_NAMESPACE { +extern "C" void __cxa_finalize(void *); -namespace internal { -void call_exit_callbacks(); -} +namespace LIBC_NAMESPACE { LLVM_LIBC_FUNCTION(void, exit, (int status)) { - internal::call_exit_callbacks(); + __cxa_finalize(nullptr); quick_exit(status); __builtin_unreachable(); } 

[petrhosek]

I slightly prefer the original version where we only execute the if body in the case of an error and continue otherwise.

[michaelrj-google]

LGTM