[Signal] Allow llvm clients to opt into one-shot SIGPIPE handling

Allow clients of the llvm library to opt-in to one-shot SIGPIPE
handling, instead of forcing them to undo llvm's SIGPIPE handler
registration (which is brittle).

The current behavior is preserved for all llvm-derived tools (except
lldb) by means of a default-`true` flag in the InitLLVM constructor.

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.

Differential Revision: https://reviews.llvm.org/D70277

1 files changed, 1 insertions, 20 deletions

diff --git a/lldb/tools/driver/Driver.cpp b/lldb/tools/driver/Driver.cpp
index 2070e55d7d2..b77350190be 100644
--- a/lldb/tools/driver/Driver.cpp
+++ b/lldb/tools/driver/Driver.cpp
@@ -810,7 +810,7 @@ int main(int argc, char const *argv[])
 {
   // Setup LLVM signal handlers and make sure we call llvm_shutdown() on
   // destruction.
-  llvm::InitLLVM IL(argc, argv);
+  llvm::InitLLVM IL(argc, argv, /*InstallPipeSignalExitHandler=*/false);
 
   // Parse arguments.
   LLDBOptTable T;
@@ -841,25 +841,6 @@ int main(int argc, char const *argv[])
   }
   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);