From a789d1d26b29683f0279269bdca970add1c6a164 Mon Sep 17 00:00:00 2001
From: "rmcilroy@chromium.org"
 <rmcilroy@chromium.org@4c0a9323-5329-0410-9bdc-e9ce6186880e>
Date: Tue, 6 May 2014 09:18:30 +0000
Subject: Add support for CFI based stack walking on Arm64.

This CL adds CFI based stack walking support for Arm64 to BreakPad along with
unit tests.  The Arm64 CFI stack walker is based on the Arm CFI stack walker

BUG=367367,335641,354405
R=blundell@chromium.org, mark@chromium.org

Review URL: https://breakpad.appspot.com/1664002

git-svn-id: http://google-breakpad.googlecode.com/svn/trunk@1325 4c0a9323-5329-0410-9bdc-e9ce6186880e
---
 src/processor/stackwalker_arm64.cc | 73 ++++++++++++++++++++++++++++++++++++--
 1 file changed, 71 insertions(+), 2 deletions(-)

(limited to 'src/processor/stackwalker_arm64.cc')

diff --git a/src/processor/stackwalker_arm64.cc b/src/processor/stackwalker_arm64.cc
index f82c9cbf..31119a97 100644
--- a/src/processor/stackwalker_arm64.cc
+++ b/src/processor/stackwalker_arm64.cc
@@ -78,8 +78,77 @@ StackFrame* StackwalkerARM64::GetContextFrame() {
 StackFrameARM64* StackwalkerARM64::GetCallerByCFIFrameInfo(
     const vector<StackFrame*> &frames,
     CFIFrameInfo* cfi_frame_info) {
-  // Obtaining the stack frame from CFI info is not yet supported for ARM64.
-  return NULL;
+  StackFrameARM64* last_frame = static_cast<StackFrameARM64*>(frames.back());
+
+  static const char* register_names[] = {
+    "x0",  "x1",  "x2",  "x3",  "x4",  "x5",  "x6",  "x7",
+    "x8",  "x9",  "x10", "x11", "x12", "x13", "x14", "x15",
+    "x16", "x17", "x18", "x19", "x20", "x21", "x22", "x23",
+    "x24", "x25", "x26", "x27", "x28", "x29", "x30", "sp",
+    "pc",  NULL
+  };
+
+  // Populate a dictionary with the valid register values in last_frame.
+  CFIFrameInfo::RegisterValueMap<uint64_t> callee_registers;
+  for (int i = 0; register_names[i]; i++) {
+    if (last_frame->context_validity & StackFrameARM64::RegisterValidFlag(i))
+      callee_registers[register_names[i]] = last_frame->context.iregs[i];
+  }
+
+  // Use the STACK CFI data to recover the caller's register values.
+  CFIFrameInfo::RegisterValueMap<uint64_t> caller_registers;
+  if (!cfi_frame_info->FindCallerRegs(callee_registers, *memory_,
+                                      &caller_registers)) {
+    return NULL;
+  }
+  // Construct a new stack frame given the values the CFI recovered.
+  scoped_ptr<StackFrameARM64> frame(new StackFrameARM64());
+  for (int i = 0; register_names[i]; i++) {
+    CFIFrameInfo::RegisterValueMap<uint64_t>::iterator entry =
+      caller_registers.find(register_names[i]);
+    if (entry != caller_registers.end()) {
+      // We recovered the value of this register; fill the context with the
+      // value from caller_registers.
+      frame->context_validity |= StackFrameARM64::RegisterValidFlag(i);
+      frame->context.iregs[i] = entry->second;
+    } else if (19 <= i && i <= 29 && (last_frame->context_validity &
+                                      StackFrameARM64::RegisterValidFlag(i))) {
+      // If the STACK CFI data doesn't mention some callee-saves register, and
+      // it is valid in the callee, assume the callee has not yet changed it.
+      // Registers r19 through r29 are callee-saves, according to the Procedure
+      // Call Standard for the ARM AARCH64 Architecture, which the Linux ABI
+      // follows.
+      frame->context_validity |= StackFrameARM64::RegisterValidFlag(i);
+      frame->context.iregs[i] = last_frame->context.iregs[i];
+    }
+  }
+  // If the CFI doesn't recover the PC explicitly, then use .ra.
+  if (!(frame->context_validity & StackFrameARM64::CONTEXT_VALID_PC)) {
+    CFIFrameInfo::RegisterValueMap<uint64_t>::iterator entry =
+      caller_registers.find(".ra");
+    if (entry != caller_registers.end()) {
+      frame->context_validity |= StackFrameARM64::CONTEXT_VALID_PC;
+      frame->context.iregs[MD_CONTEXT_ARM64_REG_PC] = entry->second;
+    }
+  }
+  // If the CFI doesn't recover the SP explicitly, then use .cfa.
+  if (!(frame->context_validity & StackFrameARM64::CONTEXT_VALID_SP)) {
+    CFIFrameInfo::RegisterValueMap<uint64_t>::iterator entry =
+      caller_registers.find(".cfa");
+    if (entry != caller_registers.end()) {
+      frame->context_validity |= StackFrameARM64::CONTEXT_VALID_SP;
+      frame->context.iregs[MD_CONTEXT_ARM64_REG_SP] = entry->second;
+    }
+  }
+
+  // If we didn't recover the PC and the SP, then the frame isn't very useful.
+  static const uint64_t essentials = (StackFrameARM64::CONTEXT_VALID_SP
+                                     | StackFrameARM64::CONTEXT_VALID_PC);
+  if ((frame->context_validity & essentials) != essentials)
+    return NULL;
+
+  frame->trust = StackFrame::FRAME_TRUST_CFI;
+  return frame.release();
 }
 
 StackFrameARM64* StackwalkerARM64::GetCallerByStackScan(
-- 
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