1 files changed, 106 insertions, 8 deletions

diff --git a/src/processor/stackwalker_arm.cc b/src/processor/stackwalker_arm.cc
index 4b15593d..0af27a32 100644
--- a/src/processor/stackwalker_arm.cc
+++ b/src/processor/stackwalker_arm.cc
@@ -31,14 +31,17 @@
 //
 // See stackwalker_arm.h for documentation.
 //
-// Author: Mark Mentovai, Ted Mielczarek
+// Author: Mark Mentovai, Ted Mielczarek, Jim Blandy
 
 
-#include "processor/stackwalker_arm.h"
 #include "google_breakpad/processor/call_stack.h"
 #include "google_breakpad/processor/memory_region.h"
+#include "google_breakpad/processor/source_line_resolver_interface.h"
 #include "google_breakpad/processor/stack_frame_cpu.h"
+#include "processor/cfi_frame_info.h"
 #include "processor/logging.h"
+#include "processor/scoped_ptr.h"
+#include "processor/stackwalker_arm.h"
 
 namespace google_breakpad {
 
@@ -50,8 +53,8 @@ StackwalkerARM::StackwalkerARM(const SystemInfo *system_info,
                                SymbolSupplier *supplier,
                                SourceLineResolverInterface *resolver)
     : Stackwalker(system_info, memory, modules, supplier, resolver),
-      context_(context) {
-}
+      context_(context), 
+      context_frame_validity_(StackFrameARM::CONTEXT_VALID_ALL) { }
 
 
 StackFrame* StackwalkerARM::GetContextFrame() {
@@ -65,7 +68,7 @@ StackFrame* StackwalkerARM::GetContextFrame() {
   // The instruction pointer is stored directly in a register (r15), so pull it
   // straight out of the CPU context structure.
   frame->context = *context_;
-  frame->context_validity = StackFrameARM::CONTEXT_VALID_ALL;
+  frame->context_validity = context_frame_validity_;
   frame->instruction = frame->context.iregs[15];
 
   return frame;
@@ -78,9 +81,104 @@ StackFrame* StackwalkerARM::GetCallerFrame(const CallStack *stack) {
     return NULL;
   }
 
-  // TODO: Can't actually walk the stack on ARM without the CFI data.
-  // Implement this when the CFI symbol dumper changes have landed.
-  return NULL;
+  const vector<StackFrame *> &frames = *stack->frames();
+  StackFrameARM *last_frame = static_cast<StackFrameARM *>(frames.back());
+
+  // See if we have DWARF call frame information covering this address.
+  scoped_ptr<CFIFrameInfo> cfi_frame_info(resolver_
+                                          ->FindCFIFrameInfo(last_frame));
+  if (cfi_frame_info == NULL)
+    // Unfortunately, CFI is our only option on the ARM for now. If we
+    // add a second strategy, we should put each one in its own function.
+    return NULL;
+
+  static const char *register_names[] = {
+    "r0",  "r1",  "r2",  "r3",  "r4",  "r5",  "r6",  "r7",
+    "r8",  "r9",  "r10", "r11", "r12", "sp",  "lr",  "pc",
+    "f0",  "f1",  "f2",  "f3",  "f4",  "f5",  "f6",  "f7",
+    "fps", "cpsr",
+    NULL
+  };
+
+  // Populate a dictionary with the valid register values in last_frame.
+  CFIFrameInfo::RegisterValueMap<u_int32_t> callee_registers;
+  for (int i = 0; register_names[i]; i++)
+    if (last_frame->context_validity & StackFrameARM::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<u_int32_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<StackFrameARM> frame(new StackFrameARM());
+  for (int i = 0; register_names[i]; i++) {
+    CFIFrameInfo::RegisterValueMap<u_int32_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 |= StackFrameARM::RegisterValidFlag(i);
+      frame->context.iregs[i] = entry->second;
+    } else if (4 <= i && i <= 11 && (last_frame->context_validity &
+                                     StackFrameARM::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 r4 through r11 are callee-saves, according to the Procedure
+      // Call Standard for the ARM Architecture, which the Linux ABI follows.
+      frame->context_validity |= StackFrameARM::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 & StackFrameARM::CONTEXT_VALID_PC)) {
+    CFIFrameInfo::RegisterValueMap<u_int32_t>::iterator entry =
+      caller_registers.find(".ra");
+    if (entry != caller_registers.end()) {
+      frame->context_validity |= StackFrameARM::CONTEXT_VALID_PC;
+      frame->context.iregs[MD_CONTEXT_ARM_REG_PC] = entry->second;
+    }
+  }
+  // If the CFI doesn't recover the SP explicitly, then use .cfa.
+  if (! (frame->context_validity & StackFrameARM::CONTEXT_VALID_SP)) {
+    CFIFrameInfo::RegisterValueMap<u_int32_t>::iterator entry =
+      caller_registers.find(".cfa");
+    if (entry != caller_registers.end()) {
+      frame->context_validity |= StackFrameARM::CONTEXT_VALID_SP;
+      frame->context.iregs[MD_CONTEXT_ARM_REG_SP] = entry->second;
+    }
+  }
+
+  // If we didn't recover the PC and the SP, then the frame isn't very useful.
+  static const int essentials = (StackFrameARM::CONTEXT_VALID_SP
+                                 | StackFrameARM::CONTEXT_VALID_PC);
+  if ((frame->context_validity & essentials) != essentials)
+    return NULL;
+
+  // An instruction address of zero marks the end of the stack.
+  if (frame->context.iregs[MD_CONTEXT_ARM_REG_PC] == 0)
+    return NULL;
+
+  // If the new stack pointer is at a lower address than the old, then
+  // that's clearly incorrect. Treat this as end-of-stack to enforce
+  // progress and avoid infinite loops.
+  if (frame->context.iregs[MD_CONTEXT_ARM_REG_SP]
+      < last_frame->context.iregs[MD_CONTEXT_ARM_REG_SP])
+    return NULL;
+
+  // The new frame's context's PC is the return address, which is one
+  // instruction past the instruction that caused us to arrive at the
+  // callee. Set new_frame->instruction to one less than the PC. This won't
+  // reference the beginning of the call instruction, but it's at least
+  // within it, which is sufficient to get the source line information to
+  // match up with the line that contains the function call. Callers that
+  // require the exact return address value may access
+  // frame->context.iregs[MD_CONTEXT_ARM_REG_PC].
+  frame->instruction = frame->context.iregs[MD_CONTEXT_ARM_REG_PC] - 1;
+
+  return frame.release();
 }