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Commit 279843e1 authored by Christopher Ferris's avatar Christopher Ferris
Browse files

Use process_vm_readv to read memory. 

Modify BacktracePtrace::Read to use the process_vm_readv syscall
instead of doing multiple ptrace calls.

Test: Ran the backtrace unit tests on host and on x86_64 emulator.

Change-Id: I24c2787f6713d8eb44312f3aa751d1f6d9d34719
parent bd6c6eb0

libbacktrace/BacktracePtrace.cpp

+12 −33
Original line number Diff line number Diff line
@@ -17,6 +17,7 @@ 
#include <errno.h>

#include <stdint.h>

#include <string.h>

#include <sys/uio.h>

#include <sys/param.h>

#include <sys/ptrace.h>

#include <sys/types.h>
@@ -72,42 +73,20 @@ size_t BacktracePtrace::Read(uintptr_t addr, uint8_t* buffer, size_t bytes) { 
  if (!BacktraceMap::IsValid(map) || !(map.flags & PROT_READ)) {

    return 0;

  }



  bytes = MIN(map.end - addr, bytes);

  size_t bytes_read = 0;

  word_t data_word;

  size_t align_bytes = addr & (sizeof(word_t) - 1);

  if (align_bytes != 0) {

    if (!PtraceRead(Tid(), addr & ~(sizeof(word_t) - 1), &data_word)) {

      return 0;

    }

    size_t copy_bytes = MIN(sizeof(word_t) - align_bytes, bytes);

    memcpy(buffer, reinterpret_cast<uint8_t*>(&data_word) + align_bytes, copy_bytes);

    addr += copy_bytes;

    buffer += copy_bytes;

    bytes -= copy_bytes;

    bytes_read += copy_bytes;

  }



  size_t num_words = bytes / sizeof(word_t);

  for (size_t i = 0; i < num_words; i++) {

    if (!PtraceRead(Tid(), addr, &data_word)) {

      return bytes_read;

    }

    memcpy(buffer, &data_word, sizeof(word_t));

    buffer += sizeof(word_t);

    addr += sizeof(word_t);

    bytes_read += sizeof(word_t);

  }

  struct iovec local_io;

  local_io.iov_base = buffer;

  local_io.iov_len = bytes;



  size_t left_over = bytes & (sizeof(word_t) - 1);

  if (left_over) {

    if (!PtraceRead(Tid(), addr, &data_word)) {

      return bytes_read;

    }

    memcpy(buffer, &data_word, left_over);

    bytes_read += left_over;

  struct iovec remote_io;

  remote_io.iov_base = reinterpret_cast<void*>(addr);

  remote_io.iov_len = bytes;



  ssize_t bytes_read = process_vm_readv(Tid(), &local_io, 1, &remote_io, 1, 0);

  if (bytes_read == -1) {

    return 0;

  }

  return bytes_read;

  return static_cast<size_t>(bytes_read);

#endif

}