[PATCH] D13818: [compiler-rt] [msan] Unify aarch64 mapping

[Adhemerval Zanella via llvm-commits]

zatrazz added inline comments.

================
Comment at: lib/msan/msan.h:89
@@ -70,3 +88,3 @@
 # define LINEARIZE_MEM(mem) \
   (((uptr)(mem) & ~0x7C00000000ULL) ^ 0x100000000ULL)
 # define MEM_TO_SHADOW(mem) (LINEARIZE_MEM((mem)) + 0x4000000000ULL)
----------------
eugenis wrote:
> This is probably out of scope of this review, but could your elaborate, and maybe add a comment, about the constraints that led to this complex mapping function? For example, a list of all address ranges that must be in "app" regions would help.
> 
> This mapping limits the applications to roughly 1/7th of the address space on 39 bit VMA and only 1/30th on 42 bit VMA. Could we do any better?
> 
This is exactly what I am struggling with current aarch64 39 and 42-bit VMA contraints regarding PIE positioning. The memory segments are:

0000000000-0010000000: both 39 and 42 for own programs segments
5500000000-5600000000: 39-bits PIE program segments
7f80000000-7000000000: 39-bits libraries segments

2aa00000000-2ab00000000: 42-bits PIE program segments
3ff00000000-3ffffffffff: 42-bits libraries segments

I am trying to increase the segments size, but it is hard to come up with a single transformation that works on both 39 and 42-bit VMA that maps 39-bit to 39-bits and also works for 42-bits. I open to suggestions.


http://reviews.llvm.org/D13818