[libunwind] Inform ASan that resumption is noreturn

[smeenai]

Summary

If you're building libunwind instrumented with ASan, _Unwind_RaiseException
will poison the stack and then transfer control in a manner which isn't
understood by ASan, so the stack will remain poisoned. This can cause
false positives, e.g. if you call an uninstrumented function (so it
doesn't re-poison the stack) after catching an exception. Add a call to
__asan_handle_no_return inside __unw_resume to get ASan to unpoison
the stack and avoid this.

__unw_resume seems like the appropriate place to make this call, since
it's used for resumption by all unwind implementations except SJLJ. SJLJ
uses __builtin_longjmp to handle resumption, which is already
recognized as noreturn (and therefore ASan adds the __asan_handle_no_return
call itself), so it doesn't need any special handling.

PR32434 is somewhat similar (in particular needing a component built
without ASan to trigger the bug), and rG781ef03e1012, the fix for that
bug, adds an interceptor for _Unwind_RaiseException. This interceptor
won't always be triggered though, e.g. if you statically link the
unwinder into libc++abi in a way that prevents interposing the unwinder
functions (e.g. marking the symbols as hidden, using --exclude-libs,
or using -Bsymbolic). rG53335d6d86d5 makes __cxa_throw call
__asan_handle_no_return explicitly, to similarly avoid relying on
interception.

[smeenai]

Lint

[compnerd]

Thanks for adding that comment - I think that the cleanup routine may be confusing otherwise.

libunwind/src/libunwind.cpp

 //===----------------------------------------------------------------------===//
 
 #include <libunwind.h>
 
 #include "libunwind_ext.h"
 #include "config.h"
 
 #include <stdlib.h>
+#if __has_feature(address_sanitizer)
+#include <sanitizer/asan_interface.h>
+#endif
 
 
 #if !defined(__USING_SJLJ_EXCEPTIONS__)
 #include "AddressSpace.hpp"
 #include "UnwindCursor.hpp"
 
 using namespace libunwind;
 
 /// internal object to represent this processes address space
 LocalAddressSpace LocalAddressSpace::sThisAddressSpace;
if (info->end_ip == 0)
     return UNW_ENOINFO;
   return UNW_ESUCCESS;
 }
 _LIBUNWIND_WEAK_ALIAS(__unw_get_proc_info, unw_get_proc_info)
 
 /// Resume execution at cursor position (aka longjump).
 _LIBUNWIND_HIDDEN int __unw_resume(unw_cursor_t *cursor) {
   _LIBUNWIND_TRACE_API("__unw_resume(cursor=%p)", static_cast<void *>(cursor));
+#if __has_feature(address_sanitizer)
+  // Inform the ASan runtime that now might be a good time to clean stuff up.
+  __asan_handle_no_return();
+#endif
   AbstractUnwindCursor *co = (AbstractUnwindCursor *)cursor;
   co->jumpto();
   return UNW_EUNSPEC;
 }
 _LIBUNWIND_WEAK_ALIAS(__unw_resume, unw_resume)
 
 /// Get name of function at cursor position in stack frame.
 _LIBUNWIND_HIDDEN int __unw_get_proc_name(unw_cursor_t *cursor, char *buf,