Redesign syscallbuf to always unwind on interruption

CMakeLists.txt

@@ -912,6 +912,7 @@ set(BASIC_TESTS
   daemon
   desched_blocking_poll
   desched_sigkill
+  desched_sigreturn
   detach_state
   detach_threads
   detach_sigkill

src/DiversionSession.cc

@@ -72,9 +72,10 @@ static void process_syscall_arch(Task* t, int syscallno) {
   if (syscallno == t->session().syscall_number_for_rrcall_rdtsc()) {
     uint64_t rdtsc_value = static_cast<DiversionSession*>(&t->session())->next_rdtsc_value();
     LOG(debug) << "Faking rrcall_rdtsc syscall with value " << rdtsc_value;
-    remote_ptr<uint64_t> out_param(t->regs().arg1());
-    t->write_mem(out_param, rdtsc_value);
-    finish_emulated_syscall_with_ret(t, 0);
+    Registers r = t->regs();
+    r.set_dx(rdtsc_value >> 32);
+    t->set_regs(r);
+    finish_emulated_syscall_with_ret(t, (uint32_t)rdtsc_value);
     return;
   }
 

src/Monkeypatcher.h

@@ -125,24 +125,34 @@ class Monkeypatcher {
   };
   std::vector<ExtendedJumpPage> extended_jump_pages;
 
-  bool is_jump_stub_instruction(remote_code_ptr p, bool include_safearea);
-  // Return the breakpoint instruction (i.e. the last branch back to caller)
-  // if we are on the exit path in the jump stub
-  remote_code_ptr get_jump_stub_exit_breakpoint(remote_code_ptr ip, RecordTask *t);
 
   struct patched_syscall {
     // Pointer to hook inside the syscall_hooks array, which gets initialized
     // once and is fixed afterwars.
     const syscall_patch_hook *hook;
+    remote_ptr<uint8_t> patch_addr;
+    remote_ptr<uint8_t> stub_addr;
     size_t size;
     uint16_t safe_prefix = 0;
     uint16_t safe_suffix = 0;
   };
 
+  patched_syscall *find_jump_stub(remote_code_ptr ip, bool include_safearea);
+  bool is_jump_stub_instruction(remote_code_ptr p, bool include_safearea) {
+    return (bool)find_jump_stub(p, include_safearea);
+  }
+
+  patched_syscall *find_syscall_patch(remote_code_ptr patch_location);
+
+  // Return the breakpoint instruction (i.e. the last branch back to caller)
+  // if we are on the exit path in the jump stub
+  remote_code_ptr get_jump_stub_exit_breakpoint(remote_code_ptr ip, RecordTask *t);
   /**
    * Addresses/lengths of syscallbuf stubs.
    */
-  std::map<remote_ptr<uint8_t>, patched_syscall> syscallbuf_stubs;
+  std::vector<patched_syscall> syscall_stub_list;
+  std::map<remote_ptr<uint8_t>, int> syscallbuf_stubs_by_extended_patch;
+  std::map<remote_ptr<uint8_t>, int> syscallbuf_stubs_by_patch_addr;
 
 private:
   /**