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flang: Fix build with latest libc++ #127362

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Merged
merged 5 commits into from
Feb 19, 2025
Merged

flang: Fix build with latest libc++ #127362

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e8e1e76
flang: Fix build with latest libc++
tstellar Feb 15, 2025
9b0da99
Fix formatting
tstellar Feb 16, 2025
71da309
Better fix
tstellar Feb 17, 2025
e735865
Fix formatting
tstellar Feb 17, 2025
81c0e53
Merge remote-tracking branch 'origin/main' into flang-libcxx-fix
tstellar Feb 18, 2025
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7 changes: 6 additions & 1 deletion flang/runtime/io-api-minimal.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -150,7 +150,12 @@ bool IODEF(OutputLogical)(Cookie cookie, bool truth) {
// Provide own definition for `std::__libcpp_verbose_abort` to avoid dependency
// on the version provided by libc++.

void std::__libcpp_verbose_abort(char const *format, ...) {
#if !defined(_LIBCPP_VERBOSE_ABORT_NOEXCEPT)
#define _LIBCPP_VERBOSE_ABORT_NOEXCEPT
#endif

void std::__libcpp_verbose_abort(
char const *format, ...) _LIBCPP_VERBOSE_ABORT_NOEXCEPT {
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@ldionne ldionne Feb 17, 2025

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The right way of fixing this would be:

void std::__libcpp_verbose_abort(char const *format, ...)
    noexcept(noexcept(std::__libcpp_verbose_abort("")))
{
  // ...
}

This allows unconditionally using the right noexcept-ness based on how the base function has been declared.

About the more general question of whether libc++ supports being used header-only (without linking against the dylib), the answer is no, but some stuff will still happen to work if you do that. That's a brittle setup though, for example I expect that you would encounter a linker error if you tried using std::shared_ptr or std::sort(int*, int*) anywhere since those are in the dylib. Is there a reason why you don't link against the libc++ built library?

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@mmuetzel mmuetzel Feb 17, 2025

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Is there a reason why you don't link against the libc++ built library?

That is a very good question that I was pondering myself repeatedly.
I hope it is ok to ask @sscalpone for clarification.

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@tstellar tstellar Feb 18, 2025

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@ldionne I've implemented your suggested fix.

va_list list;
va_start(list, format);
std::vfprintf(stderr, format, list);
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