Instead of printing absolute addresses use relative ones so they can be used later to decode the stack trace.
## Motivation
It’s quite common to release apps without debug symbols while keeping them internally. Currently the lib prints absolute addresses which require the base address to decode them using symbols. With this change, the base address won’t be needed as values are relative to the beginning of the loaded module/binary.
The implementation for unix is **straightforward** as the existing code is used. For Windows, I’ve implemented similar logic using Windows API.
## Manual testing of Windows implementation
Here are 2 runs of `trivial_windbg_lib.exe` with .pdb and without .pdb file:
```jsx
>./trivial_windbg_lib.exe
0# boost::stacktrace::basic_stacktrace<std::allocator<boost::stacktrace::frame> >::init at C:\Users\czarneckim\repositories\boost\boost\stacktrace\stacktrace.hpp:110
1# main at C:\Users\czarneckim\repositories\boost\libs\stacktrace\test\test_trivial.cpp:14
2# __scrt_common_main_seh at D:\a\_work\1\s\src\vctools\crt\vcstartup\src\startup\exe_common.inl:288
3# BaseThreadInitThunk in C:\WINDOWS\System32\KERNEL32.DLL
4# RtlUserThreadStart in C:\WINDOWS\SYSTEM32\ntdll.dll
> mv ./trivial_windbg_lib.pdb{,_}
> ./trivial_windbg_lib.exe
0# 0x0000000000001DE3 in C:\Users\czarneckim\repositories\boost\bin.v2\libs\stacktrace\test\trivial_windbg_lib.test\msvc-14.3\release\x86_64\asynch-exceptions-on\cxxstd-latest-iso\debug-symbols-on\threading-multi\trivial_windbg_lib.exe
1# 0x0000000000001FEE in C:\Users\czarneckim\repositories\boost\bin.v2\libs\stacktrace\test\trivial_windbg_lib.test\msvc-14.3\release\x86_64\asynch-exceptions-on\cxxstd-latest-iso\debug-symbols-on\threading-multi\trivial_windbg_lib.exe
2# 0x000000000000246C in C:\Users\czarneckim\repositories\boost\bin.v2\libs\stacktrace\test\trivial_windbg_lib.test\msvc-14.3\release\x86_64\asynch-exceptions-on\cxxstd-latest-iso\debug-symbols-on\threading-multi\trivial_windbg_lib.exe
3# BaseThreadInitThunk in C:\WINDOWS\System32\KERNEL32.DLL
4# RtlUserThreadStart in C:\WINDOWS\SYSTEM32\ntdll.dll
> mv ./trivial_windbg_lib.pdb{_,}
> winaddr2line.exe -f -e trivial_windbg_lib.pdb 0x0000000000001DE3
boost::stacktrace::basic_stacktrace<std::allocator<boost::stacktrace::frame> >::init
C:\Users\czarneckim\repositories\boost\boost\stacktrace\stacktrace.hpp:110
```
I’ve also decoded the returned address using x64dbg running `trivial_windbg_lib.exe+0x0000000000001DE3`:
## Control
As it was suggested in #180, the new logic is enabled by default, but can be disabled with `BOOST_STACKTRACE_DISABLE_OFFSET_ADDR_BASE` (With non header-only mode, it requires rebuilding the lib)
Now `boost_stacktrace.lib` provides the symbol `boost_stacktrace_impl_return_nullptr` for static and shared build.
For header only library, to make the symbol available **automatically**, the only way AFAIK is to export it. We may also consider provide a configuration macro to opt-out the exported symbol, and user need to manually define the non-exported symbol somewhere in their binaries.
Closes#177 .
std::current_exception() makes a copy of current exception object
into returned std::exception_ptr. So the tracking of the original
exception object and its stacktrace are lost.
