[Bug bootstrap/63888] [5 Regression] bootstrap failed when configured with -with-build-config=bootstrap-asan --disable-werror

["y.gribov at samsung dot com" <gcc-bugzilla@gcc.gnu.org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=63888

--- Comment #13 from Yury Gribov <y.gribov at samsung dot com> ---
(In reply to Kostya Serebryany from comment #12)
> But for this example in C the globals will not get instrumented, unless 
> -fno-common is given.

BTW I think everyone already pairs this with -fsanitize=address, otherwise
sanitization of globals becomes so weak.

>> If LLVM uses global symbols instead of local aliases, it is more expensive.
>> You can have aliases/weakrefs etc. to symbols, and those still aren't ODR
>> violations.
> 
> But these again should not be instrumented by asan at all. No? 

Wouldn't that cause false negatives for internal references to local aliases?

> Never seen a case like this ("registered multiple times for multiple
> addresses").
> Can you give an example?

How about this: say some global variable xyz is defined both in executable and
in shared library. Now
1) if xyz isn't exported from executable, it will not be available to shlib; so
exe's internal references will bind to exe's definition but shlib's references
will bind to shlib's definition
2) if xyz is exported from executable but shlib is linked with -Bsymbolic,
shlib's internal references will bind to shlib's implementation
3) RTLD_DEEPBIND could also alter symbol resolution order in a shlib