Statically linking it with libstdc ++ and folly broken because of experimental/exception_tracer

[neogenie]

In commit: 8140959#diff-1e7de1ae2d059d21e1dd75d5812d5a34b0222cef273b7c3a2af62eb747f9d20a

Permits including folly/experimental/exception_tracer/ in the cmake build.

Closes: #1524.

experimental/exception_tracer library became a part of main CMakeList.txt file and now a part of main folly.a library. But...

This make broken logic described in library annotation:

Exception tracer library

This library allows you to inspect the exception stack at runtime. The library can be used in three ways:

Link in the exception_tracer_base library. You get access to the functions in ExceptionTracer.h, but no stack traces. This has no runtime overhead, and is compliant with the C++ ABI.

Link in the (full) exception_tracer library. You get access to the functions in ExceptionTracer.h, the std::terminate and std::unexpected handlers are installed by default, and you get full stack traces with all exceptions. This has some runtime overhead (the stack trace must be captured and stored whenever an exception is thrown) added to throw and catch, but no runtime overhead otherwise. This is less portable (depends on internal details of GNU's libstdc++).

LD_PRELOAD libexceptiontracer.so. This is equivalent to #2 above, but requires no link-time changes. On the other hand, you need to ensure that libexceptiontracer.so is compiled with the same compiler and flags as your binary, and the usual caveats about LD_PRELOAD apply (it propagates to child processes, etc)

In principle, it is incorrect because the file ExceptionTracerLib.cpp ignores FOLLY_HAVE_ELF & FOLLY_HAVE_DWARF definitions, although relevant libraries may not be available on the build platform.

And most dramatically, it made it impossible to build an application by statically linking it with libstdc ++ and folly.

[100%] Linking CXX executable 
/usr/lib/gcc/x86_64-linux-gnu/11/libstdc++.a(eh_catch.o): In function `__cxa_begin_catch':
(.text.__cxa_begin_catch+0x0): multiple definition of `__cxa_begin_catch'
/usr/local/lib/libfolly.a(ExceptionTracerLib.cpp.o):/tmp/build/folly/folly/experimental/exception_tracer/ExceptionTracerLib.cpp:123: first defined here

It would be nice to rollback these changes or still make it cleaner by providing the necessary compilation options.

[kvtb]

It won't work with static linking :(
because of dlsym to get original functions:

folly/folly/experimental/exception_tracer/ExceptionTracerLib.cpp

Lines 116 to 117 in 8140959

	static auto orig_cxa_rethrow = reinterpret_cast<decltype(&__cxa_rethrow)>(
	dlsym(RTLD_NEXT, "__cxa_rethrow"));

[kvtb]

Something like https://stackoverflow.com/a/3053921/15239223 should be used to handle static linking

[mhx]

I haven't seen a rationale/context in #1524 for why exactly exception_tracer should be part of folly. Why was it a problem to have it as a separate library?

I also just found out that static builds for one of my projects are broken because of this.

@yfeldblum, is it really intentional to break static builds linking against folly?

[mhx]

ping

[draveness]

ping

[fzhedu]

change the way to overwrite __cxa_throw:

extern "C" {
void __real___cxa_throw(...);
void __wrap___cxa_throw(...) {
    // print track trace
    __real___cxa_throw(...);
}
}

linking: -WL, -wrap=__cxa_throw

folly/folly/experimental/exception_tracer/ExceptionTracerLib.cpp

[qc00]

FYI, folly's CMake now has an option to disable exception_tracer