RFR(S): 8252407: Build failure with gcc-8+ and asan

[Kim Barrett]

> On Sep 28, 2020, at 11:13 AM, Eric Liu <eric.c.liu at arm.com> wrote:
> 
> Hi, 
> 
> Thanks for looking at this.
> 
> For gcc-10, it's hard to make 'strncpy' all right with asan enabled (approaches we talked previous don't work). 
> I'm trying to find a better way to avoid using compile pragma. I suppose it would be better to use 'memcpy' 
> to replace 'strncpy'.
> 
> 
> Thanks,
> Eric

I don't think using memory functions in place of string functions for string
manipulation is really an improvement.

I did a bit of experimenting.

With gcc10.2, and using the --enable-asan configure option, we get a
-Wstringop-truncation warning in CompilerCounters::set_current_method, even
after careful adjustment of the code to use the documented idiom for
avoiding that warning.

I initially wondered whether this might be only in fastdebug builds, where
we also define _FORTIFY_SOURCE=2.  The asan faq
https://github.com/google/sanitizers/wiki/AddressSanitizer#faq
says asan doesn't work well with _FORTIFY_SOURCE.

But the same warning occurs in a release build, where we aren't defining
_FORTIFY_SOURCE.

At this point all I can conclude is that --enable-asan (i.e.
-fsanitize=address) is simply incompatible with -Wstringop-truncation, at
least through gcc10.  That seems like a bug that someone should report.
(Might be same as or related to https://gcc.gnu.org/bugzilla/show_bug.cgi?id=85650)

We don't normally build with -fsanitize=address; that's something that
someone might want to turn on sometimes for testing or debugging, but I
don't think we're planning to have it always on, even in debug builds.

Since it seems to be incompatible with various other options that we *do*
normally use, I think the way to allow --enable-asan to be (possibly) usable
is in the build system at configure time. That is, the --enable-asan
configure option should, in addition to adding -fsanitize=address, also (1)
disable -Wstringop-truncation and (2) disable the defining of
_FORTIFY_SOURCE in fastdebug builds.  It looks like making those changes
involves conditionalizing their addition/removal using ${ASAN_ENABLED}.

Scattering pragmas for disabling -Wstringop-truncation doesn't cut it.