core_handler: coredump handler to produce minidump

On Linux, it is possible to register a core handler via
/proc/sys/kernel/core_pattern. Doing so invokes the core handler when
a process crash. The core_handler uses /proc/<pid>/mem to access the
process memory. This way it is not necessary to process the full
coredump which takes time and consumes memory.

In order to profit from this core handler, for example, one can
integrate dump_syms into Yocto and generate an archive with the
breakpad symbols of all the binaries in the rootfs. Minidumps are
especially useful on embedded systems since they are lightweight and
provide contextual information.

Change-Id: I9298d81159029cefb81c915831db54884310ad05
Reviewed-on: https://chromium-review.googlesource.com/c/breakpad/breakpad/+/2536917
Reviewed-by: Mike Frysinger <vapier@chromium.org>

src/client/linux/minidump_writer/linux_core_dumper.cc

@@ -137,6 +137,16 @@ bool LinuxCoreDumper::EnumerateThreads() {
     return false;
   }
 
+  char proc_mem_path[NAME_MAX];
+  if (BuildProcPath(proc_mem_path, pid_, "mem")) {
+    int fd = open(proc_mem_path, O_RDONLY | O_LARGEFILE | O_CLOEXEC);
+    if (fd != -1) {
+      core_.SetProcMem(fd);
+    } else {
+      fprintf(stderr, "Cannot open %s (%s)\n", proc_mem_path, strerror(errno));
+    }
+  }
+
   core_.SetContent(mapped_core_file_.content());
   if (!core_.IsValid()) {
     fprintf(stderr, "Invalid core dump file\n");

src/common/linux/elf_core_dump.cc

@@ -34,6 +34,7 @@
 
 #include <stddef.h>
 #include <string.h>
+#include <unistd.h>
 
 namespace google_breakpad {
 
@@ -95,16 +96,29 @@ size_t ElfCoreDump::Note::AlignedSize(size_t size) {
 
 // Implementation of ElfCoreDump.
 
-ElfCoreDump::ElfCoreDump() {}
+ElfCoreDump::ElfCoreDump() : proc_mem_fd_(-1) {}
 
 ElfCoreDump::ElfCoreDump(const MemoryRange& content)
-    : content_(content) {
+    : content_(content), proc_mem_fd_(-1) {}
+
+ElfCoreDump::~ElfCoreDump() {
+  if (proc_mem_fd_ != -1) {
+    close(proc_mem_fd_);
+    proc_mem_fd_ = -1;
+  }
 }
 
 void ElfCoreDump::SetContent(const MemoryRange& content) {
   content_ = content;
 }
 
+void ElfCoreDump::SetProcMem(int fd) {
+  if (proc_mem_fd_ != -1) {
+    close(proc_mem_fd_);
+  }
+  proc_mem_fd_ = fd;
+}
+
 bool ElfCoreDump::IsValid() const {
   const Ehdr* header = GetHeader();
   return (header &&
@@ -163,6 +177,16 @@ bool ElfCoreDump::CopyData(void* buffer, Addr virtual_address, size_t length) {
       }
     }
   }
+
+  /* fallback: if available, read from /proc/<pid>/mem */
+  if (proc_mem_fd_ != -1) {
+    off_t offset = virtual_address;
+    ssize_t r = pread(proc_mem_fd_, buffer, length, offset);
+    if (r < ssize_t(length)) {
+      return false;
+    }
+    return true;
+  }
   return false;
 }
 

src/common/linux/elf_core_dump.h

@@ -106,6 +106,8 @@ class ElfCoreDump {
   // Constructor that takes the core dump content from |content|.
   explicit ElfCoreDump(const MemoryRange& content);
 
+  ~ElfCoreDump();
+
   // Sets the core dump content to |content|.
   void SetContent(const MemoryRange& content);
 
@@ -139,9 +141,15 @@ class ElfCoreDump {
   // an empty note if no note is found.
   Note GetFirstNote() const;
 
+  // Sets the mem fd.
+  void SetProcMem(const int fd);
+
  private:
   // Core dump content.
   MemoryRange content_;
+
+  // Descriptor for /proc/<pid>/mem.
+  int proc_mem_fd_;
 };
 
 }  // namespace google_breakpad

src/tools/linux/core_handler/core_handler.cc

@@ -0,0 +1,146 @@
+// Copyright (c) 2020, Google Inc.
+// All rights reserved.
+//
+// Redistribution and use in source and binary forms, with or without
+// modification, are permitted provided that the following conditions are
+// met:
+//
+//     * Redistributions of source code must retain the above copyright
+// notice, this list of conditions and the following disclaimer.
+//     * Redistributions in binary form must reproduce the above
+// copyright notice, this list of conditions and the following disclaimer
+// in the documentation and/or other materials provided with the
+// distribution.
+//     * Neither the name of Google Inc. nor the names of its
+// contributors may be used to endorse or promote products derived from
+// this software without specific prior written permission.
+//
+// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+// "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+// LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+// A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+// OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+// SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+// LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+// DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+// THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+// (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+// OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+
+// core_handler.cc: A tool to handle coredumps on Linux
+
+#include <pwd.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <sys/mman.h>
+#include <sys/types.h>
+#include <syslog.h>
+#include <unistd.h>
+#include <sstream>
+
+#include "client/linux/minidump_writer/linux_core_dumper.h"
+#include "client/linux/minidump_writer/minidump_writer.h"
+#include "common/scoped_ptr.h"
+
+namespace {
+
+using google_breakpad::AppMemoryList;
+using google_breakpad::LinuxCoreDumper;
+using google_breakpad::MappingList;
+using google_breakpad::scoped_array;
+
+// Size of the core dump to read in order to access all the threads
+// descriptions.
+//
+// The first section is the note0 section which contains the thread states. On
+// x86-64 a typical thread description take about 1432B. Reading 1 MB allows
+// several hundreds of threads.
+const int core_read_size = 1024 * 1024;
+
+void ShowUsage(const char* argv0) {
+  fprintf(stderr, "Usage: %s <process id> <minidump file>\n\n", argv0);
+  fprintf(stderr,
+          "A tool which serves as a core dump handler and produces "
+          "minidump files.\n");
+  fprintf(stderr, "Please refer to the online documentation:\n");
+  fprintf(stderr,
+          "https://chromium.googlesource.com/breakpad/breakpad/+/HEAD"
+          "/docs/linux_core_handler.md\n");
+}
+
+bool WriteMinidumpFromCore(const char* filename,
+                           const char* core_path,
+                           const char* procfs_override) {
+  MappingList mappings;
+  AppMemoryList memory_list;
+  LinuxCoreDumper dumper(0, core_path, procfs_override);
+  return google_breakpad::WriteMinidump(filename, mappings, memory_list,
+                                        &dumper);
+}
+
+bool HandleCrash(pid_t pid, const char* procfs_dir, const char* md_filename) {
+  int r = 0;
+  scoped_array<char> buf(new char[core_read_size]);
+  while (r != core_read_size) {
+    int ret = read(STDIN_FILENO, &buf[r], core_read_size - r);
+    if (ret == 0) {
+      break;
+    } else if (ret == -1) {
+      return false;
+    }
+    r += ret;
+  }
+
+  int fd = memfd_create("core_file", MFD_CLOEXEC);
+  if (fd == -1) {
+    return false;
+  }
+
+  int w = write(fd, &buf[0], r);
+  if (w != r) {
+    close(fd);
+    return false;
+  }
+
+  std::stringstream core_file_ss;
+  core_file_ss << "/proc/self/fd/" << fd;
+  std::string core_file(core_file_ss.str());
+
+  if (!WriteMinidumpFromCore(md_filename, core_file.c_str(), procfs_dir)) {
+    close(fd);
+    return false;
+  }
+  close(fd);
+
+  return true;
+}
+
+}  // namespace
+
+int main(int argc, char* argv[]) {
+  int ret = EXIT_FAILURE;
+
+  if (argc != 3) {
+    ShowUsage(argv[0]);
+    return ret;
+  }
+
+  const char* pid_str = argv[1];
+  const char* md_filename = argv[2];
+  pid_t pid = atoi(pid_str);
+
+  std::stringstream proc_dir_ss;
+  proc_dir_ss << "/proc/" << pid_str;
+  std::string proc_dir(proc_dir_ss.str());
+
+  openlog("core_handler", 0, 0);
+  if (HandleCrash(pid, proc_dir.c_str(), md_filename)) {
+    syslog(LOG_NOTICE, "Minidump generated at %s\n", md_filename);
+    ret = EXIT_SUCCESS;
+  } else {
+    syslog(LOG_ERR, "Cannot generate minidump %s\n", md_filename);
+  }
+  closelog();
+
+  return ret;
+}