From 3958f8060ac0adccd977c0fab7a53d45f3fce58d Mon Sep 17 00:00:00 2001
From: Christopher Ferris <cferris@google.com>
Date: Wed, 1 Feb 2017 15:44:40 -0800
Subject: Elf interface for new unwinder.

This cl includes the code to read arm unwind information from a shared
library.

Bug: 23762183

Test: Passes all unit tests. I can dump the arm unwind information
Test: for an arm shared library.
Change-Id: I43501ea2eab843b81de8bd5128401dd1971af8d3
---
 libunwindstack/ElfInterfaceArm.cpp | 127 +++++++++++++++++++++++++++++++++++++
 1 file changed, 127 insertions(+)
 create mode 100644 libunwindstack/ElfInterfaceArm.cpp

(limited to 'libunwindstack/ElfInterfaceArm.cpp')

diff --git a/libunwindstack/ElfInterfaceArm.cpp b/libunwindstack/ElfInterfaceArm.cpp
new file mode 100644
index 000000000..e15732073
--- /dev/null
+++ b/libunwindstack/ElfInterfaceArm.cpp
@@ -0,0 +1,127 @@
+/*
+ * Copyright (C) 2016 The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#include <elf.h>
+#include <stdint.h>
+
+#include "ArmExidx.h"
+#include "ElfInterface.h"
+#include "ElfInterfaceArm.h"
+#include "Machine.h"
+#include "Memory.h"
+#include "Regs.h"
+
+bool ElfInterfaceArm::FindEntry(uint32_t pc, uint64_t* entry_offset) {
+  if (start_offset_ == 0 || total_entries_ == 0) {
+    return false;
+  }
+
+  // Need to subtract the load_bias from the pc.
+  if (pc < load_bias_) {
+    return false;
+  }
+  pc -= load_bias_;
+
+  size_t first = 0;
+  size_t last = total_entries_;
+  while (first < last) {
+    size_t current = (first + last) / 2;
+    uint32_t addr = addrs_[current];
+    if (addr == 0) {
+      if (!GetPrel31Addr(start_offset_ + current * 8, &addr)) {
+        return false;
+      }
+      addrs_[current] = addr;
+    }
+    if (pc == addr) {
+      *entry_offset = start_offset_ + current * 8;
+      return true;
+    }
+    if (pc < addr) {
+      last = current;
+    } else {
+      first = current + 1;
+    }
+  }
+  if (last != 0) {
+    *entry_offset = start_offset_ + (last - 1) * 8;
+    return true;
+  }
+  return false;
+}
+
+bool ElfInterfaceArm::GetPrel31Addr(uint32_t offset, uint32_t* addr) {
+  uint32_t data;
+  if (!memory_->Read32(offset, &data)) {
+    return false;
+  }
+
+  // Sign extend the value if necessary.
+  int32_t value = (static_cast<int32_t>(data) << 1) >> 1;
+  *addr = offset + value;
+  return true;
+}
+
+#if !defined(PT_ARM_EXIDX)
+#define PT_ARM_EXIDX 0x70000001
+#endif
+
+bool ElfInterfaceArm::HandleType(uint64_t offset, uint32_t type) {
+  if (type != PT_ARM_EXIDX) {
+    return false;
+  }
+
+  Elf32_Phdr phdr;
+  if (!memory_->Read(offset, &phdr, &phdr.p_vaddr, sizeof(phdr.p_vaddr))) {
+    return true;
+  }
+  if (!memory_->Read(offset, &phdr, &phdr.p_memsz, sizeof(phdr.p_memsz))) {
+    return true;
+  }
+  // The load_bias_ should always be set by this time.
+  start_offset_ = phdr.p_vaddr - load_bias_;
+  total_entries_ = phdr.p_memsz / 8;
+  return true;
+}
+
+bool ElfInterfaceArm::Step(uint64_t pc, Regs* regs, Memory* process_memory) {
+  return StepExidx(pc, regs, process_memory) ||
+      ElfInterface32::Step(pc, regs, process_memory);
+}
+
+bool ElfInterfaceArm::StepExidx(uint64_t pc, Regs* regs, Memory* process_memory) {
+  RegsArm* regs_arm = reinterpret_cast<RegsArm*>(regs);
+  // First try arm, then try dwarf.
+  uint64_t entry_offset;
+  if (!FindEntry(pc, &entry_offset)) {
+    return false;
+  }
+  ArmExidx arm(regs_arm, memory_, process_memory);
+  arm.set_cfa(regs_arm->sp());
+  if (arm.ExtractEntryData(entry_offset) && arm.Eval()) {
+    // If the pc was not set, then use the LR registers for the PC.
+    if (!arm.pc_set()) {
+      regs_arm->set_pc((*regs_arm)[ARM_REG_LR]);
+      (*regs_arm)[ARM_REG_PC] = regs_arm->pc();
+    } else {
+      regs_arm->set_pc((*regs_arm)[ARM_REG_PC]);
+    }
+    regs_arm->set_sp(arm.cfa());
+    (*regs_arm)[ARM_REG_SP] = regs_arm->sp();
+    return true;
+  }
+  return false;
+}
-- 
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