Revert "Use process_vm_readv to read memory."

This reverts commit 279843e1397aff2aedb5e5ffe513893fa1f6767f.

Bug: 32806783

Change-Id: I61df26d979a8139a571ff5a6442fb5499ca20547
Test: Verified that the stack and read data works with the revert.

1 files changed, 33 insertions, 12 deletions

diff --git a/libbacktrace/BacktracePtrace.cpp b/libbacktrace/BacktracePtrace.cpp
index 148c41810..fd8b7134f 100644
--- a/libbacktrace/BacktracePtrace.cpp
+++ b/libbacktrace/BacktracePtrace.cpp
@@ -17,7 +17,6 @@
 #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>
@@ -73,20 +72,42 @@ 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);
 
-  struct iovec local_io;
-  local_io.iov_base = buffer;
-  local_io.iov_len = bytes;
+  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;
+  }
 
-  struct iovec remote_io;
-  remote_io.iov_base = reinterpret_cast<void*>(addr);
-  remote_io.iov_len = 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);
+  }
 
-  ssize_t bytes_read = process_vm_readv(Tid(), &local_io, 1, &remote_io, 1, 0);
-  if (bytes_read == -1) {
-    return 0;
+  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;
   }
-  return static_cast<size_t>(bytes_read);
+  return bytes_read;
 #endif
 }