Fix debugging of terminal applications on Linux

On modern linux distributions (Ubuntu >= 10.10, Debian >= Wheezy),
trying to debug a terminal application fails, with
"ptrace: Operation not permitted".

In order to allow the debugger to attach to the created process, the
process itself needs to inform the kernel of the debugging process.

Task-number: QTCREATORBUG-3509
Change-Id: I68670426fad18cbe3b7cce9d57633e58e631e025
Reviewed-by: Oswald Buddenhagen <oswald.buddenhagen@digia.com>
Reviewed-by: hjk <hjk121@nokiamail.com>

src/libs/utils/consoleprocess_unix.cpp

@@ -162,6 +162,7 @@ bool ConsoleProcess::start(const QString &program, const QString &args)
               << msgPromptToClose()
               << workingDirectory()
               << (d->m_tempFile ? d->m_tempFile->fileName() : QString())
+              << QString::number(getpid())
               << pcmd << pargs.toUnixArgs();
 
     QString xterm = allArgs.takeFirst();

src/libs/utils/process_stub_unix.c

@@ -47,6 +47,16 @@
 #include <errno.h>
 #include <assert.h>
 
+#ifdef __linux__
+#include <sys/prctl.h>
+
+// Enable compilation with older header that doesn't contain this constant
+// for running on newer libraries that do support it
+#ifndef PR_SET_PTRACER
+#define PR_SET_PTRACER 0x59616d61
+#endif
+#endif
+
 /* For OpenBSD */
 #ifndef EPROTO
 # define EPROTO EINVAL
@@ -90,6 +100,7 @@ enum {
     ArgMsg,
     ArgDir,
     ArgEnv,
+    ArgPid,
     ArgExe
 };
 
@@ -289,6 +300,7 @@ int main(int argc, char *argv[])
 
             /* Get a SIGTRAP after exec() has loaded the new program. */
 #ifdef __linux__
+            prctl(PR_SET_PTRACER, atoi(argv[ArgPid]));
             ptrace(PTRACE_TRACEME);
 #else
             ptrace(PT_TRACE_ME, 0, 0, 0);