Add a framework for intercepting system calls

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@6190 91177308-0d34-0410-b5e6-96231b3b80d8

lib/ExecutionEngine/JIT/Intercept.cpp

@@ -0,0 +1,52 @@
+//===-- Intercept.cpp - System function interception routines -------------===//
+//
+// If a function call occurs to an external function, the JIT is designed to use
+// dlsym on the current process to find a function to call.  This is useful for
+// calling system calls and library functions that are not available in LLVM.
+// Some system calls, however, need to be handled specially.  For this reason,
+// we intercept some of them here and use our own stubs to handle them.
+//
+//===----------------------------------------------------------------------===//
+
+#include "VM.h"
+#include <dlfcn.h>    // dlsym access
+
+//===----------------------------------------------------------------------===//
+// Function stubs that are invoked instead of raw system calls
+//===----------------------------------------------------------------------===//
+
+// NoopFn - Used if we have nothing else to call...
+static void NoopFn() {}
+
+// jit_exit - Used to intercept the "exit" system call.
+static void jit_exit(int Status) {
+  exit(Status);  // Do nothing for now.
+}
+
+// jit_atexit - Used to intercept the "at_exit" system call.
+static int jit_atexit(void (*Fn)(void)) {
+  atexit(Fn);    // Do nothing for now.
+}
+
+//===----------------------------------------------------------------------===//
+// 
+/// getPointerToNamedFunction - This method returns the address of the specified
+/// function by using the dlsym function call.  As such it is only useful for
+/// resolving library symbols, not code generated symbols.
+///
+void *VM::getPointerToNamedFunction(const std::string &Name) {
+  // Check to see if this is one of the functions we want to intercept...
+  if (Name == "exit") return jit_exit;
+  if (Name == "at_exit") return jit_atexit;
+
+  // If it's an external function, look it up in the process image...
+  void *Ptr = dlsym(0, Name.c_str());
+  if (Ptr == 0) {
+    std::cerr << "WARNING: Cannot resolve fn '" << Name
+	      << "' using a dummy noop function instead!\n";
+    Ptr = (void*)NoopFn;
+  }
+  
+  return Ptr;
+}
+