add support for the vFile:fstat packet

## Purpose
Add support for lldb's `vFile:fstat` packet to ds2 debug and platform
sessions. Fixes #135.

## Overview
* Add `fstat` method to the `File` class and implement it for POSIX.
Leave the Windows implementation unimplemented (as is the rest of
`File`)
* Call the new `File::fstat` method when is `vFile:fstat` packet is
received.

## Problem Details
Several of the lldb tests rely on `vFile:fstat` to fetch files from the
device, and these tests fail against ds2 because it is not implemented.

The `vFile:fstat` packet isn't documented. The implementation is based
on the expectation of the lldb test case
`TestGdbRemotePlatformFile.TestGdbRemotePlatformFile.test_platform_file_fstat_llgs`,
which now passes with this change.

## Validation
Once this PR and a some additionalchanges are merged, most of the
`TestGdbRemotePlatformFile` tests succeed with ds2 running on Android
and Linux and can be enabled in CI. They do not all pass with this PR
alone.

Co-authored-by: Saleem Abdulrasool <[email protected]>

Author: andrurogerz

Headers/DebugServer2/GDBRemote/DummySessionDelegateImpl.h

@@ -247,6 +247,8 @@ class DummySessionDelegateImpl : public SessionDelegate {
                           uint64_t &size) override;
   ErrorCode onFileGetMode(Session &session, std::string const &path,
                           uint32_t &mode) const override;
+  ErrorCode onFileFstat(Session &session, int fd,
+                       ByteVector &buffer) const override;
 
   ErrorCode onQueryProcessList(Session &session, ProcessInfoMatch const &match,
                                bool first, ProcessInfo &info) const override;

Headers/DebugServer2/GDBRemote/Mixins/FileOperationsMixin.h

@@ -49,6 +49,7 @@ template <typename T> class FileOperationsMixin : public T {
                           uint64_t &size) override;
   ErrorCode onFileGetMode(Session &session, std::string const &path,
                           uint32_t &mode) const override;
+  ErrorCode onFileFstat(Session &session, int fd, ByteVector &buffer) const override;
   ErrorCode onFileRemove(Session &session, std::string const &path) override;
 
 protected:

Headers/DebugServer2/GDBRemote/SessionDelegate.h

@@ -274,6 +274,8 @@ class SessionDelegate {
                                   uint64_t &size) = 0;
   virtual ErrorCode onFileGetMode(Session &session, std::string const &path,
                                   uint32_t &mode) const = 0;
+  virtual ErrorCode onFileFstat(Session &session, int fd,
+                               ByteVector &buffer) const = 0;
 
   virtual ErrorCode onQueryProcessList(Session &session,
                                        ProcessInfoMatch const &match,

Headers/DebugServer2/Host/File.h

@@ -47,6 +47,7 @@ class File {
 public:
   ErrorCode pread(ByteVector &buf, uint64_t &count, uint64_t offset);
   ErrorCode pwrite(ByteVector const &buf, uint64_t &count, uint64_t offset);
+  ErrorCode fstat(ByteVector &buffer) const;
 
 public:
   bool valid() const { return (_fd >= 0); }

Sources/GDBRemote/DummySessionDelegateImpl.cpp

@@ -295,6 +295,8 @@ DUMMY_IMPL_EMPTY(onFileGetSize, Session &, std::string const &, uint64_t &)
 
 DUMMY_IMPL_EMPTY_CONST(onFileGetMode, Session &, std::string const &, uint32_t&)
 
+DUMMY_IMPL_EMPTY_CONST(onFileFstat, Session &, int, ByteVector &)
+
 DUMMY_IMPL_EMPTY_CONST(onQueryProcessList, Session &, ProcessInfoMatch const &,
                        bool, ProcessInfo &)
 

Sources/GDBRemote/Mixins/FileOperationsMixin.hpp

@@ -101,6 +101,16 @@ ErrorCode FileOperationsMixin<T>::onFileGetMode(Session &session,
   return Host::File::fileMode(path, mode);
 }
 
+template <typename T>
+ErrorCode FileOperationsMixin<T>::onFileFstat(Session &session, int fd,
+                      ByteVector &buffer) const {
+  auto it = _openFiles.find(fd);
+  if (it == _openFiles.end())
+    return kErrorInvalidHandle;
+
+  return it->second.fstat(buffer);
+}
+
 template <typename T>
 ErrorCode FileOperationsMixin<T>::onFileRemove(Session &session,
                                                std::string const &path) {

Sources/GDBRemote/Session.cpp

@@ -3114,6 +3114,20 @@ void Session::Handle_vFile(ProtocolInterpreter::Handler const &,
     } else {
       ss << std::hex << mode;
     }
+  } else if (op == "fstat") {
+    ByteVector buffer;
+    int fd = std::strtol(&args[op_end], nullptr, 16);
+    ErrorCode error = _delegate->onFileFstat(*this, fd, buffer);
+    // Response is F, followed by the the size of the stat data (base 16),
+    // a semicolon, followed by the stat result in the binary-escaped-data
+    // encoding or F-1,errno with the errno if an error occurs, base 16
+    ss << 'F';
+    if (error != kSuccess) {
+      ss << -1 << ',' << std::hex << error;
+    } else {
+      ss << std::hex << buffer.size() << ';' << Escape(buffer);
+      escaped = true;
+    }
   } else {
     sendError(kErrorUnsupported);
     return;

Sources/Host/POSIX/File.cpp

@@ -16,6 +16,16 @@
 #include <sys/stat.h>
 #include <unistd.h>
 
+#if defined(OS_LINUX)
+#include <endian.h>
+#elif defined(OS_FREEBSD)
+#include <sys/_endian.h>
+#elif defined(OS_DARWIN)
+#include <libkern/OSByteOrder.h>
+#define htobe32(x) OSSwapHostToBigInt32(x)
+#define htobe64(x) OSSwapHostToBigInt64(x)
+#endif
+
 namespace ds2 {
 namespace Host {
 
@@ -118,6 +128,40 @@ ErrorCode File::pwrite(ByteVector const &buf, uint64_t &count,
   return _lastError = kSuccess;
 }
 
+// lldb expects stat data is returned as a packed buffer with total size of 64
+// bytes. The field order is the same as the POSIX defined stat struct. All
+// fields are encoded as 4-byte, big-endian unsigned integers except for
+// st_size, st_blksize, and st_blocks which are all 8-byte, big-endian unsigned
+// integers.
+ErrorCode File::fstat(ByteVector &buffer) const {
+  struct stat s;
+  if (::fstat(_fd, &s) < 0)
+    return Platform::TranslateError();
+
+  const auto appendInteger = [&buffer](auto value) -> void {
+    buffer.insert(buffer.end(),
+                  reinterpret_cast<uint8_t*>(&value),
+                  reinterpret_cast<uint8_t*>(&value) + sizeof(value));
+  };
+
+  appendInteger(htobe32(static_cast<uint32_t>(s.st_dev)));
+  appendInteger(htobe32(static_cast<uint32_t>(s.st_ino)));
+  appendInteger(htobe32(static_cast<uint32_t>(s.st_mode)));
+  appendInteger(htobe32(static_cast<uint32_t>(s.st_nlink)));
+  appendInteger(htobe32(static_cast<uint32_t>(s.st_uid)));
+  appendInteger(htobe32(static_cast<uint32_t>(s.st_gid)));
+  appendInteger(htobe32(static_cast<uint32_t>(s.st_rdev)));
+  appendInteger(htobe64(static_cast<uint64_t>(s.st_size)));
+  appendInteger(htobe64(static_cast<uint64_t>(s.st_blksize)));
+  appendInteger(htobe64(static_cast<uint64_t>(s.st_blocks)));
+  appendInteger(htobe32(static_cast<uint32_t>(s.st_atime)));
+  appendInteger(htobe32(static_cast<uint32_t>(s.st_mtime)));
+  appendInteger(htobe32(static_cast<uint32_t>(s.st_ctime)));
+  DS2ASSERT(buffer.size() == 64);
+
+  return kSuccess;
+}
+
 ErrorCode File::chmod(std::string const &path, uint32_t mode) {
   if (::chmod(path.c_str(), mode) < 0) {
     return Platform::TranslateError();

Sources/Host/Windows/File.cpp

@@ -29,6 +29,10 @@ ErrorCode File::pwrite(ByteVector const &buf, uint64_t &count,
   return kErrorUnsupported;
 }
 
+ErrorCode File::fstat(ByteVector &buffer) const {
+  return kErrorUnsupported;
+}
+
 ErrorCode File::chmod(std::string const &path, uint32_t mode) {
   return kErrorUnsupported;
 }