aadsm created this revision.
aadsm added reviewers: clayborg, xiaobai, labath.
Herald added a project: LLDB.
Herald added a subscriber: lldb-commits.
I'm putting this up as discussed per D62503 <https://reviews.llvm.org/D62503>.
Today when process_vm_readv fails to read the entire range we fallback to
ptrace and try to read the same range.
However, process_vm_readv does partial reads so there's no need to read again
what has already been read by process_vm_readv.
Repository:
rG LLVM Github Monorepo
https://reviews.llvm.org/D62715
Files:
lldb/source/Plugins/Process/Linux/NativeProcessLinux.cpp
Index: lldb/source/Plugins/Process/Linux/NativeProcessLinux.cpp
===================================================================
--- lldb/source/Plugins/Process/Linux/NativeProcessLinux.cpp
+++ lldb/source/Plugins/Process/Linux/NativeProcessLinux.cpp
@@ -1441,6 +1441,7 @@
Status NativeProcessLinux::ReadMemory(lldb::addr_t addr, void *buf, size_t
size,
size_t &bytes_read) {
+ bytes_read = 0;
if (ProcessVmReadvSupported()) {
// The process_vm_readv path is about 50 times faster than ptrace api. We
// want to use this syscall if it is supported.
@@ -1453,8 +1454,21 @@
remote_iov.iov_base = reinterpret_cast<void *>(addr);
remote_iov.iov_len = size;
- bytes_read = process_vm_readv(pid, &local_iov, 1, &remote_iov, 1, 0);
- const bool success = bytes_read == size;
+ auto vm_bytes_read =
+ process_vm_readv(pid, &local_iov, 1, &remote_iov, 1, 0);
+ const bool success = vm_bytes_read == size;
+ if (vm_bytes_read > 0) {
+ bytes_read = vm_bytes_read;
+ // When process_vm_readv is not able to read all the data we fallback to
+ // ptrace. However, if process_vm_readv didn't fail (vm_bytes_read != -1)
+ // and was able to some bytes avoid re-reading them with ptrace by
+ // updating the addr and size to point to the rest of the data.
+ if (!success) {
+ addr = reinterpret_cast<addr_t>(reinterpret_cast<char *>(addr) +
+ vm_bytes_read);
+ size -= vm_bytes_read;
+ }
+ }
Log *log(ProcessPOSIXLog::GetLogIfAllCategoriesSet(POSIX_LOG_PROCESS));
LLDB_LOG(log,
@@ -1468,14 +1482,14 @@
// api.
}
- unsigned char *dst = static_cast<unsigned char *>(buf);
+ unsigned char *dst = static_cast<unsigned char *>(buf) + bytes_read;
size_t remainder;
long data;
Log *log(ProcessPOSIXLog::GetLogIfAllCategoriesSet(POSIX_LOG_MEMORY));
LLDB_LOG(log, "addr = {0}, buf = {1}, size = {2}", addr, buf, size);
- for (bytes_read = 0; bytes_read < size; bytes_read += remainder) {
+ for (; bytes_read < size; bytes_read += remainder) {
Status error = NativeProcessLinux::PtraceWrapper(
PTRACE_PEEKDATA, GetID(), (void *)addr, nullptr, 0, &data);
if (error.Fail())
Index: lldb/source/Plugins/Process/Linux/NativeProcessLinux.cpp
===================================================================
--- lldb/source/Plugins/Process/Linux/NativeProcessLinux.cpp
+++ lldb/source/Plugins/Process/Linux/NativeProcessLinux.cpp
@@ -1441,6 +1441,7 @@
Status NativeProcessLinux::ReadMemory(lldb::addr_t addr, void *buf, size_t size,
size_t &bytes_read) {
+ bytes_read = 0;
if (ProcessVmReadvSupported()) {
// The process_vm_readv path is about 50 times faster than ptrace api. We
// want to use this syscall if it is supported.
@@ -1453,8 +1454,21 @@
remote_iov.iov_base = reinterpret_cast<void *>(addr);
remote_iov.iov_len = size;
- bytes_read = process_vm_readv(pid, &local_iov, 1, &remote_iov, 1, 0);
- const bool success = bytes_read == size;
+ auto vm_bytes_read =
+ process_vm_readv(pid, &local_iov, 1, &remote_iov, 1, 0);
+ const bool success = vm_bytes_read == size;
+ if (vm_bytes_read > 0) {
+ bytes_read = vm_bytes_read;
+ // When process_vm_readv is not able to read all the data we fallback to
+ // ptrace. However, if process_vm_readv didn't fail (vm_bytes_read != -1)
+ // and was able to some bytes avoid re-reading them with ptrace by
+ // updating the addr and size to point to the rest of the data.
+ if (!success) {
+ addr = reinterpret_cast<addr_t>(reinterpret_cast<char *>(addr) +
+ vm_bytes_read);
+ size -= vm_bytes_read;
+ }
+ }
Log *log(ProcessPOSIXLog::GetLogIfAllCategoriesSet(POSIX_LOG_PROCESS));
LLDB_LOG(log,
@@ -1468,14 +1482,14 @@
// api.
}
- unsigned char *dst = static_cast<unsigned char *>(buf);
+ unsigned char *dst = static_cast<unsigned char *>(buf) + bytes_read;
size_t remainder;
long data;
Log *log(ProcessPOSIXLog::GetLogIfAllCategoriesSet(POSIX_LOG_MEMORY));
LLDB_LOG(log, "addr = {0}, buf = {1}, size = {2}", addr, buf, size);
- for (bytes_read = 0; bytes_read < size; bytes_read += remainder) {
+ for (; bytes_read < size; bytes_read += remainder) {
Status error = NativeProcessLinux::PtraceWrapper(
PTRACE_PEEKDATA, GetID(), (void *)addr, nullptr, 0, &data);
if (error.Fail())
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