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Commit 87315e9d authored by Colin Cross's avatar Colin Cross
Browse files

Catch SIGBUS in HeapWalker 

SIGBUS shouldn't happen, since all of the regions being walked
were previously read out of /prod/pid/maps, but it seems to happen
rarely.  Catch it so it can produce a better log message.

Bug: 128983715
Test: atest memunreachable_test
Change-Id: I82d3941a382a0451c0dda12f5eb849ad8d697bc9
parent b4ef0beb

libmemunreachable/HeapWalker.cpp

+1 −1
Original line number Diff line number Diff line
@@ -207,6 +207,6 @@ void HeapWalker::HandleSegFault(ScopedSignalHandler& handler, int signal, siginf 
  }

}



ScopedSignalHandler::SignalFn ScopedSignalHandler::handler_;

Allocator<ScopedSignalHandler::SignalFnMap>::unique_ptr ScopedSignalHandler::handler_map_;



}  // namespace android

libmemunreachable/HeapWalker.h

+9 −3
Original line number Diff line number Diff line
@@ -52,7 +52,8 @@ class HeapWalker { 
        allocation_bytes_(0),

        roots_(allocator),

        root_vals_(allocator),

        segv_handler_(),

        sigsegv_handler_(allocator),

        sigbus_handler_(allocator),

        walking_ptr_(0),

        walking_range_{0, 0},

        segv_logged_(false),
@@ -62,10 +63,14 @@ class HeapWalker { 
    valid_mappings_range_.end = 0;

    valid_mappings_range_.begin = ~valid_allocations_range_.end;



    segv_handler_.install(

    sigsegv_handler_.install(

        SIGSEGV, [=](ScopedSignalHandler& handler, int signal, siginfo_t* siginfo, void* uctx) {

          this->HandleSegFault(handler, signal, siginfo, uctx);

        });

    sigbus_handler_.install(

        SIGBUS, [=](ScopedSignalHandler& handler, int signal, siginfo_t* siginfo, void* uctx) {

          this->HandleSegFault(handler, signal, siginfo, uctx);

        });

  }



  ~HeapWalker() {}
@@ -106,7 +111,8 @@ class HeapWalker { 
  allocator::vector<Range> roots_;

  allocator::vector<uintptr_t> root_vals_;



  ScopedSignalHandler segv_handler_;

  ScopedSignalHandler sigsegv_handler_;

  ScopedSignalHandler sigbus_handler_;

  volatile uintptr_t walking_ptr_;

  Range walking_range_;

  bool segv_logged_;

libmemunreachable/ScopedSignalHandler.h

+23 −7
Original line number Diff line number Diff line
@@ -24,6 +24,7 @@ 


#include "android-base/macros.h"



#include "Allocator.h"

#include "log.h"



namespace android {
@@ -32,17 +33,29 @@ class ScopedSignalHandler { 
 public:

  using Fn = std::function<void(ScopedSignalHandler&, int, siginfo_t*, void*)>;



  explicit ScopedSignalHandler() : signal_(-1) {}

  explicit ScopedSignalHandler(Allocator<ScopedSignalHandler> allocator) : signal_(-1) {

    if (handler_map_ == nullptr) {

      Allocator<SignalFnMap> map_allocator = allocator;

      handler_map_ = map_allocator.make_unique(allocator);

    }

  }

  ~ScopedSignalHandler() { reset(); }



  template <class F>

  void install(int signal, F&& f) {

    if (signal_ != -1) MEM_LOG_ALWAYS_FATAL("ScopedSignalHandler already installed");



    handler_ = SignalFn([=](int signal, siginfo_t* si, void* uctx) { f(*this, signal, si, uctx); });

    if (handler_map_->find(signal) != handler_map_->end()) {

      MEM_LOG_ALWAYS_FATAL("ScopedSignalHandler already installed for %d", signal);

    }



    (*handler_map_)[signal] =

        SignalFn([=](int signal, siginfo_t* si, void* uctx) { f(*this, signal, si, uctx); });



    struct sigaction act {};

    act.sa_sigaction = [](int signal, siginfo_t* si, void* uctx) { handler_(signal, si, uctx); };

    act.sa_sigaction = [](int signal, siginfo_t* si, void* uctx) {

      ((*handler_map_)[signal])(signal, si, uctx);

    };

    act.sa_flags = SA_SIGINFO;



    int ret = sigaction(signal, &act, &old_act_);
@@ -59,19 +72,22 @@ class ScopedSignalHandler { 
      if (ret < 0) {

        MEM_ALOGE("failed to uninstall segfault handler");

      }

      handler_ = SignalFn{};



      handler_map_->erase(signal_);

      if (handler_map_->empty()) {

        handler_map_.reset();

      }

      signal_ = -1;

    }

  }



 private:

  using SignalFn = std::function<void(int, siginfo_t*, void*)>;

  using SignalFnMap = allocator::unordered_map<int, SignalFn>;

  DISALLOW_COPY_AND_ASSIGN(ScopedSignalHandler);

  int signal_;

  struct sigaction old_act_;

  // TODO(ccross): to support multiple ScopedSignalHandlers handler_ would need

  // to be a static map of signals to handlers, but allocated with Allocator.

  static SignalFn handler_;

  static Allocator<SignalFnMap>::unique_ptr handler_map_;

};



}  // namespace android