vsk created this revision.
vsk added reviewers: JDevlieghere, jfb, labath.
Herald added subscribers: dexonsmith, hiraditya.
Herald added a project: LLVM.
Allow clients of the llvm library to opt-in to one-shot SIGPIPE
handling, instead of exiting with an IO error by default.
This prevents "IO error" crashes in long-lived processes (lldb is the
motivating example) which both a) load llvm as a dynamic library and b)
*really* need to ignore SIGPIPE.
As llvm signal handlers can be installed when calling into libclang
(say, via RemoveFileOnSignal), thereby overriding a previous SIG_IGN for
SIGPIPE, there is no clean way to opt-out of "exit-on-SIGPIPE" in the
current model.
https://reviews.llvm.org/D70277
Files:
clang/tools/driver/driver.cpp
lldb/tools/driver/Driver.cpp
llvm/include/llvm/Support/Signals.h
llvm/lib/Support/Unix/Signals.inc
llvm/lib/Support/Windows/Signals.inc
Index: llvm/lib/Support/Windows/Signals.inc
===================================================================
--- llvm/lib/Support/Windows/Signals.inc
+++ llvm/lib/Support/Windows/Signals.inc
@@ -560,6 +560,13 @@
// Unimplemented.
}
+void llvm::sys::SetOneShotPipeSignalFunction(void (*Handler)()) {
+ // Unimplemented.
+}
+
+void llvm::sys::DefaultOneShotPipeSignalHandler() {
+ // Unimplemented.
+}
/// Add a function to be called when a signal is delivered to the process. The
/// handler can have a cookie passed to it to identify what instance of the
Index: llvm/lib/Support/Unix/Signals.inc
===================================================================
--- llvm/lib/Support/Unix/Signals.inc
+++ llvm/lib/Support/Unix/Signals.inc
@@ -88,6 +88,9 @@
ATOMIC_VAR_INIT(nullptr);
static std::atomic<SignalHandlerFunctionType> InfoSignalFunction =
ATOMIC_VAR_INIT(nullptr);
+/// The function to call on SIGPIPE (one-time use only).
+static std::atomic<SignalHandlerFunctionType> OneShotPipeSignalFunction =
+ ATOMIC_VAR_INIT(nullptr);
namespace {
/// Signal-safe removal of files.
@@ -206,7 +209,7 @@
/// if there is, it's not our direct responsibility. For whatever reason, our
/// continued execution is no longer desirable.
static const int IntSigs[] = {
- SIGHUP, SIGINT, SIGPIPE, SIGTERM, SIGUSR2
+ SIGHUP, SIGINT, SIGTERM, SIGUSR2
};
/// Signals that represent that we have a bug, and our prompt termination has
@@ -237,7 +240,7 @@
static const size_t NumSigs =
array_lengthof(IntSigs) + array_lengthof(KillSigs) +
- array_lengthof(InfoSigs);
+ array_lengthof(InfoSigs) + 1 /* SIGPIPE */;
static std::atomic<unsigned> NumRegisteredSignals = ATOMIC_VAR_INIT(0);
@@ -322,6 +325,8 @@
registerHandler(S, SignalKind::IsKill);
for (auto S : KillSigs)
registerHandler(S, SignalKind::IsKill);
+ if (OneShotPipeSignalFunction)
+ registerHandler(SIGPIPE, SignalKind::IsKill);
for (auto S : InfoSigs)
registerHandler(S, SignalKind::IsInfo);
}
@@ -361,9 +366,10 @@
if (auto OldInterruptFunction = InterruptFunction.exchange(nullptr))
return OldInterruptFunction();
- // Send a special return code that drivers can check for, from sysexits.h.
if (Sig == SIGPIPE)
- exit(EX_IOERR);
+ if (auto OldOneShotPipeFunction =
+ OneShotPipeSignalFunction.exchange(nullptr))
+ return OldOneShotPipeFunction();
raise(Sig); // Execute the default handler.
return;
@@ -403,6 +409,16 @@
RegisterHandlers();
}
+void llvm::sys::SetOneShotPipeSignalFunction(void (*Handler)()) {
+ OneShotPipeSignalFunction.exchange(Handler);
+ RegisterHandlers();
+}
+
+void llvm::sys::DefaultOneShotPipeSignalHandler() {
+ // Send a special return code that drivers can check for, from sysexits.h.
+ exit(EX_IOERR);
+}
+
// The public API
bool llvm::sys::RemoveFileOnSignal(StringRef Filename,
std::string* ErrMsg) {
Index: llvm/include/llvm/Support/Signals.h
===================================================================
--- llvm/include/llvm/Support/Signals.h
+++ llvm/include/llvm/Support/Signals.h
@@ -84,6 +84,26 @@
/// function. Note also that the handler may be executed on a different
/// thread on some platforms.
void SetInfoSignalFunction(void (*Handler)());
+
+ /// Registers a function to be called in a "one-shot" manner when a pipe
+ /// signal is delivered to the process (i.e., on a failed write to a pipe).
+ /// After the pipe signal is handled once, the handler is unregistered.
+ ///
+ /// The LLVM signal handling code will not install any handler for the pipe
+ /// signal unless one is provided with this API (see \ref
+ /// DefaultOneShotPipeSignalHandler).
+ ///
+ /// Note that the handler is not allowed to call any non-reentrant
+ /// functions. A null handler pointer disables the current installed
+ /// function. Note also that the handler may be executed on a
+ /// different thread on some platforms.
+ ///
+ /// This is a no-op on Windows.
+ void SetOneShotPipeSignalFunction(void (*Handler)());
+
+ /// On Unix systems, this function exits with an "IO error" exit code.
+ /// This is a no-op on Windows.
+ void DefaultOneShotPipeSignalHandler();
} // End sys namespace
} // End llvm namespace
Index: lldb/tools/driver/Driver.cpp
===================================================================
--- lldb/tools/driver/Driver.cpp
+++ lldb/tools/driver/Driver.cpp
@@ -841,25 +841,6 @@
}
SBHostOS::ThreadCreated("<lldb.driver.main-thread>");
- // Install llvm's signal handlers up front to prevent lldb's handlers from
- // being ignored. This is (hopefully) a stopgap workaround.
- //
- // When lldb invokes an llvm API that installs signal handlers (e.g.
- // llvm::sys::RemoveFileOnSignal, possibly via a compiler embedded within
- // lldb), lldb's signal handlers are overriden if llvm is installing its
- // handlers for the first time.
- //
- // To work around llvm's behavior, force it to install its handlers up front,
- // and *then* install lldb's handlers. In practice this is used to prevent
- // lldb test processes from exiting due to IO_ERR when SIGPIPE is received.
- //
- // Note that when llvm installs its handlers, it 1) records the old handlers
- // it replaces and 2) re-installs the old handlers when its new handler is
- // invoked. That means that a signal not explicitly handled by lldb can fall
- // back to being handled by llvm's handler the first time it is received,
- // and then by the default handler the second time it is received.
- llvm::sys::AddSignalHandler([](void *) -> void {}, nullptr);
-
signal(SIGINT, sigint_handler);
#if !defined(_MSC_VER)
signal(SIGPIPE, SIG_IGN);
Index: clang/tools/driver/driver.cpp
===================================================================
--- clang/tools/driver/driver.cpp
+++ clang/tools/driver/driver.cpp
@@ -321,6 +321,9 @@
int main(int argc_, const char **argv_) {
noteBottomOfStack();
llvm::InitLLVM X(argc_, argv_);
+ llvm::sys::SetOneShotPipeSignalFunction(
+ llvm::sys::DefaultOneShotPipeSignalHandler);
+
SmallVector<const char *, 256> argv(argv_, argv_ + argc_);
if (llvm::sys::Process::FixupStandardFileDescriptors())
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