On Mon, Mar 11, 2019 at 11:29:39AM +0100, Eric Botcazou wrote:
> ASAN was enabled for the SPARC architecture during GCC 9 development but it
> doesn't really work on SPARC64/Linux because of the specific layout of the
> virtual memory address space. Fortunately this is (easily) fixable and the
> fix has been accepted upstream, along with other fixes for SPARC (I have
> attached the asan/asan_mapping_sparc64.h file accepted upstream).
Is the size of the virtual address space hole constant though (and will it
remain constant)?
E.g. on powerpc64 or aarch64 there are in each case like 4-5 different VA
size configurations over the last 10+ years of kernel history and
configuration options and fortunately all that is hidden inside of libasan,
if you have older gcc and run into an unsupported VA configuration, all it
takes is update libasan to one that supports it and binaries continue to
work.
While in this testcase, the VA size is hardcoded into all the generated
code. I guess running it on a VA layout that has the hole larger than
the one picked up (i.e. the high part of memory above the hole smaller;
supposedly for older kernel versions or older hw) should not be an issue,
but a big issue will be if the hole shrinks further, thus the high part of
memory above the hole grows.
Could libasan initialization if it detects just PROT_NONE mmap from the end
of hole to the start of the region it really supports (and fail if that
fails), so that backward compatibility is ensured?
> But, since GCC also hardcodes the scaling done by ASAN, this also requires a
> small adjustment to the compiler proper by means of a hook, tentatively
> called
> TARGET_ASAN_SHADOW_LEFT_SHIFT, which is defined to NULL except for SPARC. It
> yields a 100% clean ASAN testsuite on SPARC64/Linux (32-bit and 64-bit).
>
> Tested on SPARC64/Linux, SPARC/Solaris and x86-64/Linux, OK for the mainline?
>
>
> 2019-03-11 Eric Botcazou <ebotca...@adacore.com>
>
> PR sanitizer/80953
> * target.def (asan_shadow_left_shift): New hook.
> (asan_shadow_offset): Minor tweak.
> * doc/tm.texi.in: Add TARGET_ASAN_SHADOW_LEFT_SHIFT.
> * doc/tm.texi: Regenerate.
> * asan.c (asan_emit_stack_protection): Do a preliminary left shift if
> TARGET_ASAN_SHADOW_LEFT_SHIFT is positive.
> (build_shadow_mem_access): Likewise.
> * config/sparc/sparc.c (TARGET_ASAN_SHADOW_LEFT_SHIFT): Define to...
> (sparc_asan_shadow_left_shift): ...this. New function.
Also, don't you need some corresponding libsanitizer changes?
Jakub
