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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
This commit is contained in:
Christopher Ferris 2016-10-12 12:39:18 -07:00
parent bd6c6eb0e4
commit 279843e139
1 changed files with 12 additions and 33 deletions
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45
libbacktrace/BacktracePtrace.cpp
View File

@ -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
}