RFC Asan instrumentation control

[Jakub Jelinek]

On Fri, Dec 06, 2013 at 03:28:50PM +0400, Yury Gribov wrote:
> Hi all,
> 
> GCC version of Asan currently lacks options for detailed control
> over code instrumentation. These are not usually necessary but for
> embedded systems with scarce system resources Asan memory overhead
> of 2x-3x may often be unacceptable.
> 
> It seems that LLVM provides some options to allow programmer select
> which part of his code/memory he's interested in:
> * -asan-instrument-reads
> * -asan-instrument-writes
> * -asan-memintrin
> * -asan-stack
> * -asan-globals
> * -blacklist

I'm strongly against the blacklist, that is not the way things are done in
GCC, you have corresponding attribute to mark functions you don't want to
instrument, people can macroize that with
__typeof (symbol) symbol __attribute__((__no_sanitize_address__));
But in any case, you mark it in the code rather than adding externally
some symbol list.

For others, perhaps, the question is what options to use for them, because
-asan-* options are clearly unacceptable.  Perhaps best might be
--param asan-instrument-reads=0 and similar.  Note I'd prefer not to
implement ABI changing options, like making red zone size, or shadow
shift or shadow base etc. variable, it is enough that libasan, etc. doesn't
have a stable ABI in between major GCC versions, we don't want to people
have issues with library X compiled with GCC 4.9 with one asan ABI and
another with a different one.

	Jakub