[compiler-rt][XRay] Implement __xray_unpatch() and __xray_remove_handler()

Summary:
We also add one test (and the XRay testing infrastructure) to exercise
the patching and unpatching code. This uses the XRay API exported
through the headers as well, installing a custom log handler.

Depends on D23101 for the updated emitted code alignment for the
return/entry sleds.

Reviewers: rSerge, echristo, rnk

Subscribers: tberghammer, danalbert, srhines, mehdi_amini, llvm-commits

Differential Revision: https://reviews.llvm.org/D23154

git-svn-id: https://llvm.org/svn/llvm-project/compiler-rt/trunk@277971 91177308-0d34-0410-b5e6-96231b3b80d8

1 files changed, 38 insertions, 13 deletions

diff --git a/lib/xray/xray_interface.cc b/lib/xray/xray_interface.cc
index ccbe7e2f2..5ef3fc7aa 100644
--- a/lib/xray/xray_interface.cc
+++ b/lib/xray/xray_interface.cc
@@ -82,6 +82,8 @@ int __xray_set_handler(void (*entry)(int32_t, XRayEntryType)) {
   return 0;
 }
 
+int __xray_remove_handler() { return __xray_set_handler(nullptr); }
+
 std::atomic<bool> XRayPatching{false};
 
 using namespace __xray;
@@ -104,7 +106,10 @@ template <class Function> CleanupInvoker<Function> ScopeCleanup(Function Fn) {
   return CleanupInvoker<Function>{Fn};
 }
 
-XRayPatchingStatus __xray_patch() {
+// ControlPatching implements the common internals of the patching/unpatching
+// implementation. |Enable| defines whether we're enabling or disabling the
+// runtime XRay instrumentation.
+XRayPatchingStatus ControlPatching(bool Enable) {
   if (!XRayInitialized.load(std::memory_order_acquire))
     return XRayPatchingStatus::NOT_INITIALIZED; // Not initialized.
 
@@ -131,7 +136,9 @@ XRayPatchingStatus __xray_patch() {
   int32_t FuncId = 1;
   static constexpr uint8_t CallOpCode = 0xe8;
   static constexpr uint16_t MovR10Seq = 0xba41;
+  static constexpr uint16_t Jmp9Seq = 0x09eb;
   static constexpr uint8_t JmpOpCode = 0xe9;
+  static constexpr uint8_t RetOpCode = 0xc3;
   uint64_t CurFun = 0;
   for (std::size_t I = 0; I < InstrMap.Entries; I++) {
     auto Sled = InstrMap.Sleds[I];
@@ -191,12 +198,19 @@ XRayPatchingStatus __xray_patch() {
                TrampolineOffset);
         continue;
       }
-      *reinterpret_cast<uint32_t *>(Sled.Address + 2) = FuncId;
-      *reinterpret_cast<uint8_t *>(Sled.Address + 6) = CallOpCode;
-      *reinterpret_cast<uint32_t *>(Sled.Address + 7) = TrampolineOffset;
-      std::atomic_store_explicit(
-          reinterpret_cast<std::atomic<uint16_t> *>(Sled.Address), MovR10Seq,
-          std::memory_order_release);
+      if (Enable) {
+        *reinterpret_cast<uint32_t *>(Sled.Address + 2) = FuncId;
+        *reinterpret_cast<uint8_t *>(Sled.Address + 6) = CallOpCode;
+        *reinterpret_cast<uint32_t *>(Sled.Address + 7) = TrampolineOffset;
+        std::atomic_store_explicit(
+            reinterpret_cast<std::atomic<uint16_t> *>(Sled.Address), MovR10Seq,
+            std::memory_order_release);
+      } else {
+        std::atomic_store_explicit(
+            reinterpret_cast<std::atomic<uint16_t> *>(Sled.Address), Jmp9Seq,
+            std::memory_order_release);
+        // FIXME: Write out the nops still?
+      }
     }
 
     if (Sled.Kind == XRayEntryType::EXIT) {
@@ -231,15 +245,26 @@ XRayPatchingStatus __xray_patch() {
                TrampolineOffset);
         continue;
       }
-      *reinterpret_cast<uint32_t *>(Sled.Address + 2) = FuncId;
-      *reinterpret_cast<uint8_t *>(Sled.Address + 6) = JmpOpCode;
-      *reinterpret_cast<uint32_t *>(Sled.Address + 7) = TrampolineOffset;
-      std::atomic_store_explicit(
-          reinterpret_cast<std::atomic<uint16_t> *>(Sled.Address), MovR10Seq,
-          std::memory_order_release);
+      if (Enable) {
+        *reinterpret_cast<uint32_t *>(Sled.Address + 2) = FuncId;
+        *reinterpret_cast<uint8_t *>(Sled.Address + 6) = JmpOpCode;
+        *reinterpret_cast<uint32_t *>(Sled.Address + 7) = TrampolineOffset;
+        std::atomic_store_explicit(
+            reinterpret_cast<std::atomic<uint16_t> *>(Sled.Address), MovR10Seq,
+            std::memory_order_release);
+      } else {
+        std::atomic_store_explicit(
+            reinterpret_cast<std::atomic<uint8_t> *>(Sled.Address), RetOpCode,
+            std::memory_order_release);
+        // FIXME: Write out the nops still?
+      }
     }
   }
   XRayPatching.store(false, std::memory_order_release);
   PatchingSuccess = true;
   return XRayPatchingStatus::SUCCESS;
 }
+
+XRayPatchingStatus __xray_patch() { return ControlPatching(true); }
+
+XRayPatchingStatus __xray_unpatch() { return ControlPatching(false); }