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Commit 12d90296 authored by David Srbecky's avatar David Srbecky Committed by Christopher Ferris
Browse files

Cache DWARF location rules for a given pc. 

Decoding the DWARF opcodes is expensive so make sure we cache it.

This speeds unwinding in simpleperf by over a factor of 3x.

Add unit tests for this new behavior.

Bug: 77258731

Test: libbacktrace/libunwindstack unit tests on host and target.
Test: Ran debuggerd -b on various processes on target.
Change-Id: Ia516c0fa5d3e5f76746190bb4b6fdf49fd1c9388
(cherry picked from commit 3386ebad)
parent 8dc3f941

libunwindstack/DwarfCfa.cpp

+11 −2
Original line number Diff line number Diff line
@@ -50,7 +50,17 @@ bool DwarfCfa<AddressType>::GetLocationInfo(uint64_t pc, uint64_t start_offset, 
  memory_->set_cur_offset(start_offset);

  uint64_t cfa_offset;

  cur_pc_ = fde_->pc_start;

  while ((cfa_offset = memory_->cur_offset()) < end_offset && cur_pc_ <= pc) {

  loc_regs->pc_start = cur_pc_;

  while (true) {

    if (cur_pc_ > pc) {

      loc_regs->pc_end = cur_pc_;

      return true;

    }

    if ((cfa_offset = memory_->cur_offset()) >= end_offset) {

      loc_regs->pc_end = fde_->pc_end;

      return true;

    }

    loc_regs->pc_start = cur_pc_;

    operands_.clear();

    // Read the cfa information.

    uint8_t cfa_value;
@@ -129,7 +139,6 @@ bool DwarfCfa<AddressType>::GetLocationInfo(uint64_t pc, uint64_t start_offset, 
      }

    }

  }

  return true;

}



template <typename AddressType>

libunwindstack/DwarfSection.cpp

+19 −11
Original line number Diff line number Diff line
@@ -55,6 +55,9 @@ const DwarfFde* DwarfSection::GetFdeFromPc(uint64_t pc) { 
}



bool DwarfSection::Step(uint64_t pc, Regs* regs, Memory* process_memory, bool* finished) {

  // Lookup the pc in the cache.

  auto it = loc_regs_.upper_bound(pc);

  if (it == loc_regs_.end() || pc < it->second.pc_start) {

    last_error_.code = DWARF_ERROR_NONE;

    const DwarfFde* fde = GetFdeFromPc(pc);

    if (fde == nullptr || fde->cie == nullptr) {
@@ -67,9 +70,14 @@ bool DwarfSection::Step(uint64_t pc, Regs* regs, Memory* process_memory, bool* f 
    if (!GetCfaLocationInfo(pc, fde, &loc_regs)) {

      return false;

    }

    loc_regs.cie = fde->cie;



    // Store it in the cache.

    it = loc_regs_.emplace(loc_regs.pc_end, std::move(loc_regs)).first;

  }



  // Now eval the actual registers.

  return Eval(fde->cie, process_memory, loc_regs, regs, finished);

  return Eval(it->second.cie, process_memory, it->second, regs, finished);

}



template <typename AddressType>

libunwindstack/include/unwindstack/DwarfLocation.h

+9 −1
Original line number Diff line number Diff line
@@ -23,6 +23,8 @@ 


namespace unwindstack {



struct DwarfCie;



enum DwarfLocationEnum : uint8_t {

  DWARF_LOCATION_INVALID = 0,

  DWARF_LOCATION_UNDEFINED,
@@ -38,7 +40,13 @@ struct DwarfLocation { 
  uint64_t values[2];

};



typedef std::unordered_map<uint32_t, DwarfLocation> dwarf_loc_regs_t;

struct DwarfLocations : public std::unordered_map<uint32_t, DwarfLocation> {

  const DwarfCie* cie;

  // The range of PCs where the locations are valid (end is exclusive).

  uint64_t pc_start = 0;

  uint64_t pc_end = 0;

};

typedef DwarfLocations dwarf_loc_regs_t;



}  // namespace unwindstack

libunwindstack/include/unwindstack/DwarfSection.h

+2 −0
Original line number Diff line number Diff line
@@ -20,6 +20,7 @@ 
#include <stdint.h>



#include <iterator>

#include <map>

#include <unordered_map>



#include <unwindstack/DwarfError.h>
@@ -112,6 +113,7 @@ class DwarfSection { 
  std::unordered_map<uint64_t, DwarfFde> fde_entries_;

  std::unordered_map<uint64_t, DwarfCie> cie_entries_;

  std::unordered_map<uint64_t, dwarf_loc_regs_t> cie_loc_regs_;

  std::map<uint64_t, dwarf_loc_regs_t> loc_regs_;  // Single row indexed by pc_end.

};



template <typename AddressType>

libunwindstack/tests/DwarfSectionImplTest.cpp

+2 −1
Original line number Diff line number Diff line
@@ -853,7 +853,8 @@ TYPED_TEST_P(DwarfSectionImplTest, GetCfaLocationInfo_cie_cached) { 
  fde.cfa_instructions_offset = 0x6000;

  fde.cfa_instructions_end = 0x6002;



  dwarf_loc_regs_t cie_loc_regs{{6, {DWARF_LOCATION_REGISTER, {4, 0}}}};

  dwarf_loc_regs_t cie_loc_regs;

  cie_loc_regs[6] = DwarfLocation{DWARF_LOCATION_REGISTER, {4, 0}};

  this->section_->TestSetCachedCieLocRegs(0x8000, cie_loc_regs);

  this->memory_.SetMemory(0x6000, std::vector<uint8_t>{0x09, 0x04, 0x03});