[LLVMdev] [ASan] static linking on android?

[Evgeniy Stepanov]

On Tue, Sep 24, 2013 at 10:32 PM, Greg Fitzgerald <garious at gmail.com> wrote:

> > Static runtime will only intercept calls from the main executable, but
> > not from any libraries. This may work for simple standalone programs,
> > but you may run into puzzling failures.
>
> What type of failures do you mean?  Does the symbol mismatch break
> assumptions in the ASan runtime?  It's easy to imagine, for example,
> ASan missing use-after-free bugs because the call to free() is in an
> uninstrumented shared library.  But would you expect
> stack-buffer-overflow and heap-buffer-overflow detection to work as
> expected?
>

Malloc/free are special on Android - they are intercepted with bionic debug
malloc hooks, which work fine with statically linked runtime.

One failure that I recall is related to initialization order. Libraries are
initialized before the main executable, libc constructor calls malloc(),
which we do not intercept because asan_init() has not run yet. Later we get
a mismatching free(), which is fatal. I think we solved this with
.preinit_array, but then reverted, because it does not work with dalvik
apps anyway.

I think missing a pthread_create call from a library would be bad, as ASan
needs to initialize some per-thread state there.



>
> Thanks,
> Greg
>
>
> On Mon, Sep 23, 2013 at 1:42 AM, Evgeniy Stepanov <eugenis at google.com>
> wrote:
> > For the same reason we use shared runtime on OSX.
> >
> > We intercept libc calls by declaring a function with the same name in
> > the sanitizer runtime library. Glibc loader puts main executable early
> > in the symbol lookup order, which lets us interpose symbols from
> > shared libraries with symbols from statically linked sanitizer
> > runtime. Android (and AFAIK most other platforms) does not allow that,
> > which is why we need to LD_PRELOAD interceptors.
> >
> > Static runtime will only intercept calls from the main executable, but
> > not from any libraries. This may work for simple standalone programs,
> > but you may run into puzzling failures. I would be very surprised if
> > it worked for any JNI code.
> >
> >
> > On Sat, Sep 21, 2013 at 9:45 AM, Kostya Serebryany <kcc at google.com>
> wrote:
> >> +eugenis@
> >>
> >>
> >> On Sat, Sep 21, 2013 at 4:58 AM, Greg Fitzgerald <garious at gmail.com>
> wrote:
> >>>
> >>> Why does compiler-rt ship a shared object for ASan on Android instead
> >>> of a static library?  Would statically linking ASan on Android at
> >>> least be safe for standalone executables?
> >>>
> >>> And if I'm wanting to use ASan in C++ code that is invoked from an
> >>> APK, can I statically link ASan?  If not, what is the reason we need
> >>> to preload Dalvik with the ASan shared object?  I assume static
> >>> linking here would mean that ASan would miss leaks and overflows in
> >>> Dalvik, but are there other drawbacks?
> >>>
> >>> Thanks,
> >>> Greg
> >>> _______________________________________________
> >>> LLVM Developers mailing list
> >>> LLVMdev at cs.uiuc.edu         http://llvm.cs.uiuc.edu
> >>> http://lists.cs.uiuc.edu/mailman/listinfo/llvmdev
> >>
> >>
>
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