jpeach commented on PR #10326:
URL: https://github.com/apache/trafficserver/pull/10326#issuecomment-1704481010
I went down a bit of a rabbit hole on this one ....
IIUC this is a lllvm libc++ problem. `<math.h>` comes in via `<atomic>`
which comes in via `<DbgCtl.h>`
```
.. ../../../include/ts/DbgCtl.h
... /usr/local/opt/llvm/bin/../include/c++/v1/atomic
.... /usr/local/opt/llvm/bin/../include/c++/v1/cstring
.... /usr/local/opt/llvm/bin/../include/c++/v1/cmath
..... /usr/local/opt/llvm/bin/../include/c++/v1/math.h
```
Relevant libc++ header says:
```C
#if !defined(_LIBCPP_REMOVE_TRANSITIVE_INCLUDES) && _LIBCPP_STD_VER <= 20
# include <cmath>
# include <compare>
# include <type_traits>
#endif
```
So in theory, setting that define should help. However, if we do that, we
end up with a different path:
```
... /usr/local/opt/llvm/bin/../include/c++/v1/utility
.... /usr/local/opt/llvm/bin/../include/c++/v1/compare
.....
/usr/local/opt/llvm/bin/../include/c++/v1/__compare/compare_partial_order_fallback.h
...... /usr/local/opt/llvm/bin/../include/c++/v1/__compare/partial_order.h
.......
/usr/local/opt/llvm/bin/../include/c++/v1/__compare/compare_three_way.h
....... /usr/local/opt/llvm/bin/../include/c++/v1/__compare/weak_order.h
........ /usr/local/opt/llvm/bin/../include/c++/v1/__compare/strong_order.h
......... /usr/local/opt/llvm/bin/../include/c++/v1/cmath
.......... /usr/local/opt/llvm/bin/../include/c++/v1/math.h
```
And in `<cmath>` we find code like this, which unconditionally pulls
`<math.h>` into the global namespace:
```C
...
#include <math.h>
...
_LIBCPP_BEGIN_NAMESPACE_STD
...
_LIBCPP_END_NAMESPACE_STD
...
```
So yeh, c++ seems like it's a bug mess with regard to `<math.h>` symbols.
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