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Re: [PATCH][Revised] Enable libsanitizer on darwin


Hi Rainer,

The quick answer is no, although the expansion into GCC world may
require such a guideline.
We've initially implemented ASan on Linux and then ported it to
Android (which is very similar to Linux) and Mac (which is very
different), so we have little experience with porting yet.
I've summarized the differences between Linux and Mac here:
https://code.google.com/p/address-sanitizer/wiki/AddressSanitizerForMacImplementationDetails

The core things to pay attention at are function wrapping (e.g. dlsym
on Linux, mach_override on Mac), hooking the allocations/deallocations
in the program, stack unwinding (already done for x86 and ARM), thread
creation, early initialization, debug info and symbolization. Maybe
something else. In fact if any of these points work on your platform
differently than they do on Linux/Mac, you'll have to re-implement
those.

Regarding mach_override, it's a Mac OS-specific thing that we use
because dlsym doesn't reliably override functions (keywords: two-level
namespace)
This only works on x86/x86_64 and is just a bunch of ad-hoc hacks to
hot-patch the library code.
Extending the instruction table in mach_override.c is irrelevant to
porting, it's just a mean of making it work with some newer libraries
provided by Apple.
It won't work on any other OS (well, without some refactoring; in fact
it's possible to use it on Linux) or any other arch (one could rewrite
mach_override.c for ARM, but iOS doesn't allow code patching).

I'm working on a replacement for mach_override, which will compile
libasan as a dynamic library on Mac OS and preload it before running
the program.
It's not ready yet, so the easiest thing for GCC will be to add some
more instructions to mach_override and stick to it for now.

Alex

On Wed, Nov 14, 2012 at 7:08 PM, Rainer Orth
<ro@cebitec.uni-bielefeld.de> wrote:
> Hi Alex,
>
>> most certainly the functionality of asan is not intact.
>> The error messages denote that mach_override couldn't parse some of
>> the function prologues, which means some of ASan interceptors just
>> won't work.
>> In order to fix this you need to change the DEBUG definition in
>> mach_override.c, look at the bytes being parsed and fix the
>> instruction table in mach_override.c
>
> is there some guideline how to port asan to a new OS or CPU?  That would
> certainly be easier than figuring things out on your own one by one.  I
> guess several target and os port maintainers would want to do so in GCC.
>
> Thanks.
>         Rainer
>
> --
> -----------------------------------------------------------------------------
> Rainer Orth, Center for Biotechnology, Bielefeld University



-- 
Alexander Potapenko
Software Engineer
Google Moscow


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