[stacktrace] boost_stacktrace_from_exception on non-x86

From: Tim Haines (thaines.astro_at_[hidden])
Date: 2024-04-24 15:59:11

This feature is guarded by BOOST_STACKTRACE_ALWAYS_STORE_IN_PADDING, but
that is only enabled on x86 (
https://github.com/boostorg/stacktrace/blob/a33e198cf660c213e700d6f050a4641b74ea880a/src/exception_headers.h#L9-L13).
This means that

  ./bootstrap.sh --with-toolset=gcc --with-libraries=stacktrace
  ./b2 install threading=multi toolset=gcc

always fails to build on non-x86 platforms. There are three current
workarounds:

1) set boost.stacktrace.from_exception=off
2) set BOOST_STACKTRACE_LIBCXX_RUNTIME_MAY_CAUSE_MEMORY_LEAK
3) build with threading=single

(1) prevents me from using this feature. (2) shouldn't be needed on it's
face because I'm using gcc/libstdc++. (3) affects more than stacktrace.

Is this an incidental error, or is there a reason I wasn't able to deduce
as to why this feature can't be used on non-x86+libstdc++?

It seems like the check for libc++ on non-x86 can't be entirely done at
compile time. I definitely understand wanting to alert users to the dangers
of using this feature, but there also doesn't seem to be a good way of
detecting the presence of libc++ at compile time (hence the need for
https://github.com/boostorg/stacktrace/blob/a33e198cf660c213e700d6f050a4641b74ea880a/src/from_exception.cpp#L81
).

Thanks.
- Tim