Re: [PATCH][revised] fix PR sanitizer/55617

[Richard Biener <richard dot guenther at gmail dot com>]

On Sun, Feb 3, 2013 at 9:25 PM, Jack Howarth <howarth@bromo.med.uc.edu> wrote:
>    Currently darwin is unable to utilize libasan with constructors due to the lack of
> constructor priority support on that target. The asan_finish_file routine inserts an
> essential __asan_init into the array of constructors (via the __mod_init_func section).
> However the insertion occurs at the end, and due to the lack of priority support for
> constructors, these are executed from the start of the array of constructors on program
> startup. This causes code any instrumented code that executes before the __asan_init
> call to crash.
>    Since darwin sets...
>
> #undef SUPPORTS_INIT_PRIORITY
> #define SUPPORTS_INIT_PRIORITY 0
>
> in gcc/config/darwin.h, all constructors are automatically set to
>
> #define DEFAULT_INIT_PRIORITY 65535
>
> in gcc/collect2.c. Any code that attempts to set the constructor/destructor priority
> on darwin results in a compile time error of "constructor priorities are not supported".
> So asan alone should be unique in emitting priorities different from 65535 on darwin.
> The attached patch uses a va_gc vector of constructor symbol/priority records to queue
> this data as it is generated in calls to machopic_asm_out_constructor. Any instances of
> the static constructor with priority MAX_RESERVED_INIT_PRIORITY-1 emitted by asan are
> inserted safely in the front of the vector queue which retains the original order of the
> remaining constructors in the queue. The contents of the vector queue are later processed
> in a new finalize_ctors routine called from darwin_file_end if necessary. The patch also
> adds a g++.dg/asan/pr55617.C test case which is targeted to i?86-*-darwin* and x86_64-*-darwin*.
>     The patch reduces the failures observed when running....
>
> make -k check-g++ RUNTESTFLAGS="--target_board=unix'{-fsanitize=address}'"
>
> from 323 to only 85 on darwin (similar to the results on linux). The cov.C testcase also
> fails on gcc trunk with -fsanitize=address when recrafted into a dynamic shared library
> http://gcc.gnu.org/bugzilla/show_bug.cgi?id=55617#c28. This patch eliminates those
> crashes. This problem doesn't extend to when the shared library or module is dlopen'd
> (which works in stock gcc trunk and with this patch as well).
>     The patch has been bootstrap and regression tested on x86_64-apple-darwin12.
> Okay for gcc trunk?

See my other reply - this does not work for multiple TUs.

Richard.

>          Jack
> ps Unfortunately the flag_sort variable is unavailable inside of machopic_asm_out_constructor
> so we have to unconditionally test for priority == MAX_RESERVED_INIT_PRIORITY - 1.
>