This revision was automatically updated to reflect the committed changes.
Closed by commit rGcaa7e765e5ae: [lldb] Make ProcessLauncherPosixFork (mostly)
async-signal-safe (authored by labath).
Changed prior to commit:
https://reviews.llvm.org/D116165?vs=395859&id=396500#toc
Repository:
rG LLVM Github Monorepo
CHANGES SINCE LAST ACTION
https://reviews.llvm.org/D116165/new/
https://reviews.llvm.org/D116165
Files:
lldb/include/lldb/Utility/Log.h
lldb/source/Host/posix/ProcessLauncherPosixFork.cpp
lldb/source/Utility/Log.cpp
Index: lldb/source/Utility/Log.cpp
===================================================================
--- lldb/source/Utility/Log.cpp
+++ lldb/source/Utility/Log.cpp
@@ -30,7 +30,6 @@
#include <process.h>
#else
#include <unistd.h>
-#include <pthread.h>
#endif
using namespace lldb_private;
@@ -180,9 +179,6 @@
}
void Log::Initialize() {
-#ifdef LLVM_ON_UNIX
- pthread_atfork(nullptr, nullptr, &Log::DisableLoggingChild);
-#endif
InitializeLldbChannel();
}
@@ -346,11 +342,3 @@
message << payload << "\n";
WriteMessage(message.str());
}
-
-void Log::DisableLoggingChild() {
- // Disable logging by clearing out the atomic variable after forking -- if we
- // forked while another thread held the channel mutex, we would deadlock when
- // trying to write to the log.
- for (auto &c: *g_channel_map)
- c.second.m_channel.log_ptr.store(nullptr, std::memory_order_relaxed);
-}
Index: lldb/source/Host/posix/ProcessLauncherPosixFork.cpp
===================================================================
--- lldb/source/Host/posix/ProcessLauncherPosixFork.cpp
+++ lldb/source/Host/posix/ProcessLauncherPosixFork.cpp
@@ -38,43 +38,40 @@
using namespace lldb;
using namespace lldb_private;
-static void FixupEnvironment(Environment &env) {
-#ifdef __ANDROID__
- // If there is no PATH variable specified inside the environment then set the
- // path to /system/bin. It is required because the default path used by
- // execve() is wrong on android.
- env.try_emplace("PATH", "/system/bin");
-#endif
+// Begin code running in the child process
+// NB: This code needs to be async-signal safe, since we're invoking fork from
+// multithreaded contexts.
+
+static void write_string(int error_fd, const char *str) {
+ int r = write(error_fd, str, strlen(str));
+ (void)r;
}
[[noreturn]] static void ExitWithError(int error_fd,
const char *operation) {
int err = errno;
- llvm::raw_fd_ostream os(error_fd, true);
- os << operation << " failed: " << llvm::sys::StrError(err);
- os.flush();
+ write_string(error_fd, operation);
+ write_string(error_fd, " failed: ");
+ // strerror is not guaranteed to be async-signal safe, but it usually is.
+ write_string(error_fd, strerror(err));
_exit(1);
}
-static void DisableASLRIfRequested(int error_fd, const ProcessLaunchInfo &info) {
+static void DisableASLR(int error_fd) {
#if defined(__linux__)
- if (info.GetFlags().Test(lldb::eLaunchFlagDisableASLR)) {
- const unsigned long personality_get_current = 0xffffffff;
- int value = personality(personality_get_current);
- if (value == -1)
- ExitWithError(error_fd, "personality get");
-
- value = personality(ADDR_NO_RANDOMIZE | value);
- if (value == -1)
- ExitWithError(error_fd, "personality set");
- }
+ const unsigned long personality_get_current = 0xffffffff;
+ int value = personality(personality_get_current);
+ if (value == -1)
+ ExitWithError(error_fd, "personality get");
+
+ value = personality(ADDR_NO_RANDOMIZE | value);
+ if (value == -1)
+ ExitWithError(error_fd, "personality set");
#endif
}
-static void DupDescriptor(int error_fd, const FileSpec &file_spec, int fd,
- int flags) {
- int target_fd = llvm::sys::RetryAfterSignal(-1, ::open,
- file_spec.GetCString(), flags, 0666);
+static void DupDescriptor(int error_fd, const char *file, int fd, int flags) {
+ int target_fd = llvm::sys::RetryAfterSignal(-1, ::open, file, flags, 0666);
if (target_fd == -1)
ExitWithError(error_fd, "DupDescriptor-open");
@@ -88,44 +85,67 @@
::close(target_fd);
}
-[[noreturn]] static void ChildFunc(int error_fd,
- const ProcessLaunchInfo &info) {
- if (info.GetFlags().Test(eLaunchFlagLaunchInSeparateProcessGroup)) {
+namespace {
+struct ForkFileAction {
+ ForkFileAction(const FileAction &act);
+
+ FileAction::Action action;
+ int fd;
+ std::string path;
+ int arg;
+};
+
+struct ForkLaunchInfo {
+ ForkLaunchInfo(const ProcessLaunchInfo &info);
+
+ bool separate_process_group;
+ bool debug;
+ bool disable_aslr;
+ std::string wd;
+ const char **argv;
+ Environment::Envp envp;
+ std::vector<ForkFileAction> actions;
+
+ bool has_action(int fd) const {
+ for (const ForkFileAction &action : actions) {
+ if (action.fd == fd)
+ return true;
+ }
+ return false;
+ }
+};
+} // namespace
+
+[[noreturn]] static void ChildFunc(int error_fd, const ForkLaunchInfo &info) {
+ if (info.separate_process_group) {
if (setpgid(0, 0) != 0)
ExitWithError(error_fd, "setpgid");
}
- for (size_t i = 0; i < info.GetNumFileActions(); ++i) {
- const FileAction &action = *info.GetFileActionAtIndex(i);
- switch (action.GetAction()) {
+ for (const ForkFileAction &action : info.actions) {
+ switch (action.action) {
case FileAction::eFileActionClose:
- if (close(action.GetFD()) != 0)
+ if (close(action.fd) != 0)
ExitWithError(error_fd, "close");
break;
case FileAction::eFileActionDuplicate:
- if (dup2(action.GetFD(), action.GetActionArgument()) == -1)
+ if (dup2(action.fd, action.arg) == -1)
ExitWithError(error_fd, "dup2");
break;
case FileAction::eFileActionOpen:
- DupDescriptor(error_fd, action.GetFileSpec(), action.GetFD(),
- action.GetActionArgument());
+ DupDescriptor(error_fd, action.path.c_str(), action.fd, action.arg);
break;
case FileAction::eFileActionNone:
break;
}
}
- const char **argv = info.GetArguments().GetConstArgumentVector();
-
// Change working directory
- if (info.GetWorkingDirectory() &&
- 0 != ::chdir(info.GetWorkingDirectory().GetCString()))
+ if (!info.wd.empty() && 0 != ::chdir(info.wd.c_str()))
ExitWithError(error_fd, "chdir");
- DisableASLRIfRequested(error_fd, info);
- Environment env = info.GetEnvironment();
- FixupEnvironment(env);
- Environment::Envp envp = env.getEnvp();
+ if (info.disable_aslr)
+ DisableASLR(error_fd);
// Clear the signal mask to prevent the child from being affected by any
// masking done by the parent.
@@ -134,7 +154,7 @@
pthread_sigmask(SIG_SETMASK, &set, nullptr) != 0)
ExitWithError(error_fd, "pthread_sigmask");
- if (info.GetFlags().Test(eLaunchFlagDebug)) {
+ if (info.debug) {
// Do not inherit setgid powers.
if (setgid(getgid()) != 0)
ExitWithError(error_fd, "setgid");
@@ -143,6 +163,8 @@
// Close everything besides stdin, stdout, and stderr that has no file
// action to avoid leaking. Only do this when debugging, as elsewhere we
// actually rely on passing open descriptors to child processes.
+ // NB: This code is not async-signal safe, but we currently do not launch
+ // processes for debugging from within multithreaded contexts.
const llvm::StringRef proc_fd_path = "/proc/self/fd";
std::error_code ec;
@@ -157,7 +179,7 @@
// Don't close first three entries since they are stdin, stdout and
// stderr.
- if (fd > 2 && !info.GetFileActionForFD(fd) && fd != error_fd)
+ if (fd > 2 && !info.has_action(fd) && fd != error_fd)
files_to_close.push_back(fd);
}
for (int file_to_close : files_to_close)
@@ -166,7 +188,7 @@
// Since /proc/self/fd didn't work, trying the slow way instead.
int max_fd = sysconf(_SC_OPEN_MAX);
for (int fd = 3; fd < max_fd; ++fd)
- if (!info.GetFileActionForFD(fd) && fd != error_fd)
+ if (!info.has_action(fd) && fd != error_fd)
close(fd);
}
@@ -176,7 +198,7 @@
}
// Execute. We should never return...
- execve(argv[0], const_cast<char *const *>(argv), envp);
+ execve(info.argv[0], const_cast<char *const *>(info.argv), info.envp);
#if defined(__linux__)
if (errno == ETXTBSY) {
@@ -189,7 +211,7 @@
// Since this state should clear up quickly, wait a while and then give it
// one more go.
usleep(50000);
- execve(argv[0], const_cast<char *const *>(argv), envp);
+ execve(info.argv[0], const_cast<char *const *>(info.argv), info.envp);
}
#endif
@@ -198,12 +220,43 @@
ExitWithError(error_fd, "execve");
}
+// End of code running in the child process.
+
+ForkFileAction::ForkFileAction(const FileAction &act)
+ : action(act.GetAction()), fd(act.GetFD()), path(act.GetPath().str()),
+ arg(act.GetActionArgument()) {}
+
+static std::vector<ForkFileAction>
+MakeForkActions(const ProcessLaunchInfo &info) {
+ std::vector<ForkFileAction> result;
+ for (size_t i = 0; i < info.GetNumFileActions(); ++i)
+ result.emplace_back(*info.GetFileActionAtIndex(i));
+ return result;
+}
+
+static Environment::Envp FixupEnvironment(Environment env) {
+#ifdef __ANDROID__
+ // If there is no PATH variable specified inside the environment then set the
+ // path to /system/bin. It is required because the default path used by
+ // execve() is wrong on android.
+ env.try_emplace("PATH", "/system/bin");
+#endif
+ return env.getEnvp();
+}
+
+ForkLaunchInfo::ForkLaunchInfo(const ProcessLaunchInfo &info)
+ : separate_process_group(
+ info.GetFlags().Test(eLaunchFlagLaunchInSeparateProcessGroup)),
+ debug(info.GetFlags().Test(eLaunchFlagDebug)),
+ disable_aslr(info.GetFlags().Test(eLaunchFlagDisableASLR)),
+ wd(info.GetWorkingDirectory().GetPath()),
+ argv(info.GetArguments().GetConstArgumentVector()),
+ envp(FixupEnvironment(info.GetEnvironment())),
+ actions(MakeForkActions(info)) {}
+
HostProcess
ProcessLauncherPosixFork::LaunchProcess(const ProcessLaunchInfo &launch_info,
Status &error) {
- char exe_path[PATH_MAX];
- launch_info.GetExecutableFile().GetPath(exe_path, sizeof(exe_path));
-
// A pipe used by the child process to report errors.
PipePosix pipe;
const bool child_processes_inherit = false;
@@ -211,6 +264,8 @@
if (error.Fail())
return HostProcess();
+ const ForkLaunchInfo fork_launch_info(launch_info);
+
::pid_t pid = ::fork();
if (pid == -1) {
// Fork failed
@@ -221,7 +276,7 @@
if (pid == 0) {
// child process
pipe.CloseReadFileDescriptor();
- ChildFunc(pipe.ReleaseWriteFileDescriptor(), launch_info);
+ ChildFunc(pipe.ReleaseWriteFileDescriptor(), fork_launch_info);
}
// parent process
Index: lldb/include/lldb/Utility/Log.h
===================================================================
--- lldb/include/lldb/Utility/Log.h
+++ lldb/include/lldb/Utility/Log.h
@@ -211,8 +211,6 @@
static uint32_t GetFlags(llvm::raw_ostream &stream, const ChannelMap::value_type &entry,
llvm::ArrayRef<const char *> categories);
- static void DisableLoggingChild();
-
Log(const Log &) = delete;
void operator=(const Log &) = delete;
};
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