sim-se: Fix execve syscall

There were three things preventing execve from working

Firstly, the entrypoint for the new program wasn't correct. This was
fixed by calling Process::init, which adds a bias to the entrypoint.

Secondly, the uname string wasn't being copied over. This meant when the
new executable tried to run, it would think the kernel was too old to
run on, and would error out. This was fixed by copying over the uname
string (the `release` string in Process) when creating the new process.

Additionally, this patch also ensures we copy over the uname string in
the clone implementation, as otherwise a cloned thread that called
execve would crash.

Finally, we choose to not delete the new ProcessParams or the old
Process. This is done both because it matches what is done in cloneFunc,
but also because deleting the old process results in a segfault later
on.

Change-Id: I4ca201da689e9e37671b4cb477dc76fa12eecf69
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/48345
Reviewed-by: Matt Sinclair <mattdsinclair@gmail.com>
Reviewed-by: Bobby R. Bruce <bbruce@ucdavis.edu>
Maintainer: Matt Sinclair <mattdsinclair@gmail.com>
Tested-by: kokoro <noreply+kokoro@google.com>

src/sim/syscall_emul.hh

@@ -1452,6 +1452,7 @@ cloneFunc(SyscallDesc *desc, ThreadContext *tc, RegVal flags, RegVal newStack,
     pp->euid = p->euid();
     pp->gid = p->gid();
     pp->egid = p->egid();
+    pp->release = p->release;
 
     /* Find the first free PID that's less than the maximum */
     std::set<int> const& pids = p->system->PIDs;
@@ -2017,6 +2018,7 @@ execveFunc(SyscallDesc *desc, ThreadContext *tc,
     pp->errout.assign("cerr");
     pp->cwd.assign(p->tgtCwd);
     pp->system = p->system;
+    pp->release = p->release;
     /**
      * Prevent process object creation with identical PIDs (which will trip
      * a fatal check in Process constructor). The execve call is supposed to
@@ -2027,7 +2029,9 @@ execveFunc(SyscallDesc *desc, ThreadContext *tc,
      */
     p->system->PIDs.erase(p->pid());
     Process *new_p = pp->create();
-    delete pp;
+    // TODO: there is no way to know when the Process SimObject is done with
+    // the params pointer. Both the params pointer (pp) and the process
+    // pointer (p) are normally managed in python and are never cleaned up.
 
     /**
      * Work through the file descriptor array and close any files marked
@@ -2042,10 +2046,10 @@ execveFunc(SyscallDesc *desc, ThreadContext *tc,
 
     *new_p->sigchld = true;
 
-    delete p;
     tc->clearArchRegs();
     tc->setProcessPtr(new_p);
     new_p->assignThreadContext(tc->contextId());
+    new_p->init();
     new_p->initState();
     tc->activate();
     TheISA::PCState pcState = tc->pcState();