[PATCH] MC: Don't emit min version directives when -fno-integrated-as is on

[Nico Weber]

On Thu, Jan 22, 2015 at 9:00 AM, Filipe Cabecinhas <filcab at gmail.com> wrote:

> Hi all,
>
> For using cctools: use as -q, which uses the clang assembler.
>
> For afl-fuzz it's simple. You have two options:
> Use Xcode's clang, which is the same used for as -q, which afl uses
> (AFL_CLANG=`xcrun -p clang` (AFL_CXX too)).
>

Xcode's clang doesn't support -fsanitize=adress from what I can tell.


> Or
> Change afl-as.c, look for -q (lower case. Should be conditioned on
> DARWIN), change to -c. Export AFL_AS=clang (path to your top of tree clang
> that is emitting the asm that as doesn't understand).
>

This works.

Aha, looking through cctools/as/driver.c, -q just causes `clang -x
assembler ... -integrated-as -c` to be called, and I suppose my Xcode 6.1
clang doesn't understand the .macosx_version_min (that was added last
April!) yet. I agree that this patch is unnecessary, then.

Thanks!

(Maybe afl-as could call `AFL_CC ? AFL_CC : AFL_CXX ? AFL_CXX : clang` with
-x assembler -integrated-as -c instead of as -q ifdef __APPLE__ to increase
afl's it's-just-worksiness, but that's off-topic for this issue :-) ).


>
> Regards,
>
>   Filipe
>
>
> On Thursday, January 22, 2015, Nico Weber <thakis at chromium.org> wrote:
>
>> On Thu, Jan 22, 2015 at 6:05 AM, Rafael Espíndola <
>> rafael.espindola at gmail.com> wrote:
>>
>>> On 22 January 2015 at 00:36, Nico Weber <thakis at chromium.org> wrote:
>>> > I'm trying to use afl-fuzz with asan on OS X. afl-fuzz tells you to
>>> set CXX to afl-clang++ and rebuild your program. afl-clang++ then calls
>>> clang++ with -no-integrated-as and -B to a path with its own as wrapper
>>> that inserts some instrumentation assembly before calling real as. This
>>> doesn't work on OS X because clang++ writes this .macosx_version_min
>>> directive that as doesn't support. If I apply this patch, everything does
>>> work. So this seems like a useful thing to me – are there any downsides to
>>> this patch?
>>>
>>> Yes, it puts us in a direction we really don't want to go.
>>>
>>> On OS X /usr/bin/as is really old and not supported. If afl is using
>>> it instead clang that is a bug in afl.
>>>
>>
>> afl is using -no-integrated-as to munge the asm output. It doesn't care
>> which as gets run.
>>
>>
>>> The correct way of making this easier would probably be to write a
>>> program that is command line compatible with /usr/bin/as but uses MC.
>>>
>>
>> That sounds great, but until that exists this patch seems to increase
>> clang's it's-just-works-iness  by at least 8.3% for a very minor code
>> change. Once llvm-gas (or however it should be called) exists, it's no
>> longer necessary.
>>
>
>
> --
>   F
>
>
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