[PATCH] D13781: [sanitizer] Use same shadow offset for aarch64

[Adhemerval Zanella via llvm-commits]

zatrazz added a comment.

In http://reviews.llvm.org/D13781#268230, @rengolin wrote:

> Hi Adhemerval,
>
> What is the impact of this change? I remember that using 39-bits config on 42-bits broke a lot of tests. Is the addition a cure for all those problems?


I tested on 42-bit without no regressions. It will use different mappings, but I also sent a compiler-rt
to adjust this [1]. The only downside is for 39-bits it will need to cover a 42-bit VMA in TwoLevelByteMap
thus consume slight more memory in mapping (which is something I think we can live with).

> What about the other sanitizers? Some of them, like TSAN, run together with ASAN, shouldn't the settings be the same on both?


That's not true, tsan can not be run with asan (trying to use -fsanitize=address,thread issues an error).
Also conceptually it is not really possible: memory operations are handled different regarding
these two sanitizers and memory mapping is defined independently for each one. You can have some
sanitizer working together, like asan and lsan, but it is due both use the same infrastructure.

> For the next steps, do you think this will work with all the other sanitizers?


I am currently trying to make it happen for msan and it looks feasible: the strategy I am using is
to use the same instrumentation for both 39 and 42-bit VMA and use the same mapping for
both. The idea is define a transformation that will translate 39-bit segments to 39-bit shadow
addresses and for 39-bit vma only maps segments up to 39-bits. For instance, using the 
39-bit msan instrumentation scheme for a 42-bit VMA:

  {0x05500000000ULL, 0x055FFFFFFFFULL, MappingDesc::SHADOW,  "app-1"},
  {0x04000000000ULL, 0x04100000000ULL, MappingDesc::SHADOW,  "shadow-1"},
  {0x04300000000ULL, 0x04400000000ULL, MappingDesc::ORIGIN,  "origin-1"},
  {0x07000000000ULL, 0x07FFFFFFFFFULL, MappingDesc::SHADOW,  "app-2"},
  {0x04100000000ULL, 0x04300000000ULL, MappingDesc::SHADOW,  "shadow-2"},
  {0x04400000000ULL, 0x04600000000ULL, MappingDesc::ORIGIN,  "origin-2"},
  {0x2AA00000000ULL, 0x2AAFFFFFFFFULL, MappingDesc::SHADOW,  "app-3"},
  {0x2C300000000ULL, 0x2C400000000ULL, MappingDesc::SHADOW,  "shadow-3"},
  {0x2C600000000ULL, 0x2C700000000ULL, MappingDesc::ORIGIN,  "origin-3"},
  {0x2AA00000000ULL, 0x2AAFFFFFFFFULL, MappingDesc::SHADOW,  "app-4"},
  {0x2C300000000ULL, 0x2C400000000ULL, MappingDesc::SHADOW,  "shadow-4"},
  {0x2C600000000ULL, 0x2C700000000ULL, MappingDesc::ORIGIN,  "origin-4"},
  {0x3F000000000ULL, 0x3FFFFFFFFFFULL, MappingDesc::SHADOW,  "app-5"},
  {0x3C100000000ULL, 0x3C300000000ULL, MappingDesc::SHADOW,  "shadow-5"},
  {0x3C400000000ULL, 0x3C600000000ULL, MappingDesc::ORIGIN,  "origin-5"},

For 39-bit VMA libsanitizer will only map the segments until 0x8000000000 and for 42-bit 
VMA it will maps all the segments.

> cheers,

> --renato


[1] http://reviews.llvm.org/D13782


http://reviews.llvm.org/D13781