[llvm-xray] Support for PIE

When the instrumented binary is linked as PIE, we need to apply the
relative relocations to sleds. This is handled by the dynamic linker
at runtime, but when processing the file we have to do it ourselves.

Differential Revision: https://reviews.llvm.org/D55542

llvm-svn: 349120

diff --git a/llvm/lib/XRay/InstrumentationMap.cpp b/llvm/lib/XRay/InstrumentationMap.cpp
index 8431770..d33fb4a 100644 (file)
--- a/llvm/lib/XRay/InstrumentationMap.cpp
+++ b/llvm/lib/XRay/InstrumentationMap.cpp
@@ -12,12 +12,14 @@
 //===----------------------------------------------------------------------===//
 
 #include "llvm/XRay/InstrumentationMap.h"
+#include "llvm/ADT/DenseMap.h"
 #include "llvm/ADT/None.h"
 #include "llvm/ADT/STLExtras.h"
 #include "llvm/ADT/StringRef.h"
 #include "llvm/ADT/Triple.h"
 #include "llvm/ADT/Twine.h"
 #include "llvm/Object/Binary.h"
+#include "llvm/Object/ELFObjectFile.h"
 #include "llvm/Object/ObjectFile.h"
 #include "llvm/Support/DataExtractor.h"
 #include "llvm/Support/Error.h"
@@ -46,6 +48,8 @@ Optional<uint64_t> InstrumentationMap::getFunctionAddr(int32_t FuncId) const {
   return None;
 }
 
+using RelocMap = DenseMap<uint64_t, uint64_t>;
+
 static Error
 loadObj(StringRef Filename, object::OwningBinary<object::ObjectFile> &ObjFile,
           InstrumentationMap::SledContainer &Sleds,
@@ -79,6 +83,31 @@ loadObj(StringRef Filename, object::OwningBinary<object::ObjectFile> &ObjFile,
     return errorCodeToError(
         std::make_error_code(std::errc::executable_format_error));
 
+  RelocMap Relocs;
+  if (ObjFile.getBinary()->isELF()) {
+    uint32_t RelrRelocationType = [](object::ObjectFile *ObjFile) {
+      if (const auto *ELFObj = dyn_cast<object::ELF32LEObjectFile>(ObjFile))
+        return ELFObj->getELFFile()->getRelrRelocationType();
+      else if (const auto *ELFObj = dyn_cast<object::ELF32BEObjectFile>(ObjFile))
+        return ELFObj->getELFFile()->getRelrRelocationType();
+      else if (const auto *ELFObj = dyn_cast<object::ELF64LEObjectFile>(ObjFile))
+        return ELFObj->getELFFile()->getRelrRelocationType();
+      else if (const auto *ELFObj = dyn_cast<object::ELF64BEObjectFile>(ObjFile))
+        return ELFObj->getELFFile()->getRelrRelocationType();
+      else
+        return static_cast<uint32_t>(0);
+    }(ObjFile.getBinary());
+
+    for (const object::SectionRef &Section : Sections) {
+      for (const object::RelocationRef &Reloc : Section.relocations()) {
+        if (Reloc.getType() != RelrRelocationType)
+          continue;
+        if (auto AddendOrErr = object::ELFRelocationRef(Reloc).getAddend())
+          Relocs.insert({Reloc.getOffset(), *AddendOrErr});
+      }
+    }
+  }
+
   // Copy the instrumentation map data into the Sleds data structure.
   auto C = Contents.bytes_begin();
   static constexpr size_t ELF64SledEntrySize = 32;
@@ -89,6 +118,16 @@ loadObj(StringRef Filename, object::OwningBinary<object::ObjectFile> &ObjFile,
               "an XRay sled entry in ELF64."),
         std::make_error_code(std::errc::executable_format_error));
 
+  auto RelocateOrElse = [&](uint32_t Offset, uint64_t Address) {
+    if (!Address) {
+      uint64_t A = I->getAddress() + C - Contents.bytes_begin() + Offset;
+      RelocMap::const_iterator R = Relocs.find(A);
+      if (R != Relocs.end())
+        return R->second;
+    }
+    return Address;
+  };
+
   int32_t FuncId = 1;
   uint64_t CurFn = 0;
   for (; C != Contents.bytes_end(); C += ELF64SledEntrySize) {
@@ -98,8 +137,8 @@ loadObj(StringRef Filename, object::OwningBinary<object::ObjectFile> &ObjFile,
     Sleds.push_back({});
     auto &Entry = Sleds.back();
     uint32_t OffsetPtr = 0;
-    Entry.Address = Extractor.getU64(&OffsetPtr);
-    Entry.Function = Extractor.getU64(&OffsetPtr);
+    Entry.Address = RelocateOrElse(OffsetPtr, Extractor.getU64(&OffsetPtr));
+    Entry.Function = RelocateOrElse(OffsetPtr, Extractor.getU64(&OffsetPtr));
     auto Kind = Extractor.getU8(&OffsetPtr);
     static constexpr SledEntry::FunctionKinds Kinds[] = {
         SledEntry::FunctionKinds::ENTRY, SledEntry::FunctionKinds::EXIT,

diff --git a/llvm/test/tools/llvm-xray/X86/Inputs/elf64-pie.bin b/llvm/test/tools/llvm-xray/X86/Inputs/elf64-pie.bin
new file mode 100755 (executable)
index 0000000..ab2745e
Binary files /dev/null and b/llvm/test/tools/llvm-xray/X86/Inputs/elf64-pie.bin differ

diff --git a/llvm/test/tools/llvm-xray/X86/extract-instrmap-pie.ll b/llvm/test/tools/llvm-xray/X86/extract-instrmap-pie.ll
new file mode 100644 (file)
index 0000000..987aaf9
--- /dev/null
+++ b/llvm/test/tools/llvm-xray/X86/extract-instrmap-pie.ll
@@ -0,0 +1,11 @@
+; This test makes sure we can extract the instrumentation map from an
+; XRay-instrumented PIE file.
+;
+; RUN: llvm-xray extract %S/Inputs/elf64-pie.bin -s | FileCheck %s
+
+; CHECK:      ---
+; CHECK-NEXT: - { id: 1, address: 0x00000000000299C0, function: 0x00000000000299C0, kind: function-enter, always-instrument: true, function-name: {{.*foo.*}} }
+; CHECK-NEXT: - { id: 1, address: 0x00000000000299D0, function: 0x00000000000299C0, kind: function-exit, always-instrument: true, function-name: {{.*foo.*}} }
+; CHECK-NEXT: - { id: 2, address: 0x00000000000299E0, function: 0x00000000000299E0, kind: function-enter, always-instrument: true, function-name: {{.*bar.*}} }
+; CHECK-NEXT: - { id: 2, address: 0x00000000000299F6, function: 0x00000000000299E0, kind: function-exit, always-instrument: true, function-name: {{.*bar.*}} }
+; CHECK-NEXT: ...