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
diff --git a/libbacktrace/BacktracePtrace.cpp b/libbacktrace/BacktracePtrace.cpp
index fd8b713..148c418 100644
--- a/libbacktrace/BacktracePtrace.cpp
+++ b/libbacktrace/BacktracePtrace.cpp
@@ -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 @@
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
}