[PATCH] D19650: [ASan] Add shadow offset for SystemZ.

[Marcin Kościelnicki via llvm-commits]

koriakin created this revision.
koriakin added reviewers: uweigand, eugenis, kcc.
koriakin added a subscriber: llvm-commits.
koriakin set the repository for this revision to rL LLVM.
koriakin added a project: Sanitizers.

SystemZ on Linux currently has 53-bit address space.  In theory, the hardware
could support a full 64-bit address space, but that's not supported due to
kernel limitations (it'd require 5-level page tables), and there are no plans
for that.  The default process layout stays within first 4TB of address space
(to avoid creating 4-level page tables), so any offset >= (1 << 42) is fine.
Let's use 1 << 52 here, ie. exactly half the address space.

I've originally used 7 << 50 (uses top 1/8th of the address space), but ASan
runtime assumes there's some space after the shadow area.  While this is
fixable, it's simpler to avoid the issue entirely.

Also, I've originally wanted to have the shadow aligned to 1/8th the address
space, so that we can use OR like X86 to assemble the offset.  I no longer
think it's a good idea, since using ADD enables us to load the constant just
once and use it with register + register indexed addressing.

Repository:
  rL LLVM

http://reviews.llvm.org/D19650

Files:
  lib/Transforms/Instrumentation/AddressSanitizer.cpp

Index: lib/Transforms/Instrumentation/AddressSanitizer.cpp
===================================================================
--- lib/Transforms/Instrumentation/AddressSanitizer.cpp
+++ lib/Transforms/Instrumentation/AddressSanitizer.cpp
@@ -71,6 +71,7 @@
 static const uint64_t kSmallX86_64ShadowOffset = 0x7FFF8000;  // < 2G.
 static const uint64_t kLinuxKasan_ShadowOffset64 = 0xdffffc0000000000;
 static const uint64_t kPPC64_ShadowOffset64 = 1ULL << 41;
+static const uint64_t kSystemZ_ShadowOffset64 = 1ULL << 52;
 static const uint64_t kMIPS32_ShadowOffset32 = 0x0aaa0000;
 static const uint64_t kMIPS64_ShadowOffset64 = 1ULL << 37;
 static const uint64_t kAArch64_ShadowOffset64 = 1ULL << 36;
@@ -351,6 +352,7 @@
   bool IsLinux = TargetTriple.isOSLinux();
   bool IsPPC64 = TargetTriple.getArch() == llvm::Triple::ppc64 ||
                  TargetTriple.getArch() == llvm::Triple::ppc64le;
+  bool IsSystemZ = TargetTriple.getArch() == llvm::Triple::systemz;
   bool IsX86 = TargetTriple.getArch() == llvm::Triple::x86;
   bool IsX86_64 = TargetTriple.getArch() == llvm::Triple::x86_64;
   bool IsMIPS32 = TargetTriple.getArch() == llvm::Triple::mips ||
@@ -381,6 +383,8 @@
   } else {  // LongSize == 64
     if (IsPPC64)
       Mapping.Offset = kPPC64_ShadowOffset64;
+    else if (IsSystemZ)
+      Mapping.Offset = kSystemZ_ShadowOffset64;
     else if (IsFreeBSD)
       Mapping.Offset = kFreeBSD_ShadowOffset64;
     else if (IsLinux && IsX86_64) {
@@ -406,8 +410,10 @@
 
   // OR-ing shadow offset if more efficient (at least on x86) if the offset
   // is a power of two, but on ppc64 we have to use add since the shadow
-  // offset is not necessary 1/8-th of the address space.
-  Mapping.OrShadowOffset = !IsAArch64 && !IsPPC64
+  // offset is not necessary 1/8-th of the address space.  On SystemZ,
+  // we could OR the constant in a single instruction, but it's more
+  // efficient to load it once and use indexed addressing.
+  Mapping.OrShadowOffset = !IsAArch64 && !IsPPC64 && !IsSystemZ
                            && !(Mapping.Offset & (Mapping.Offset - 1));
 
   return Mapping;


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