cpu: rename the misleading inSyscall to noSquashFromTC

isSyscall was originally created because during handling of a syscall in SE
mode the threadcontext had to be updated. However, in many places this is used
in FS mode (e.g. fault handlers) and the name doesn't make much sense. The
boolean actually stops gem5 from squashing speculative and non-committed state
when a write to a threadcontext happens, so re-name the variable to something
more appropriate

4 files changed, 23 insertions, 17 deletions

diff --git a/src/cpu/inorder/cpu.cc b/src/cpu/inorder/cpu.cc
index 3dad7d1f4..5815775f9 100644
--- a/src/cpu/inorder/cpu.cc
+++ b/src/cpu/inorder/cpu.cc
@@ -786,9 +786,9 @@ InOrderCPU::init()
     BaseCPU::init();
 
     for (ThreadID tid = 0; tid < numThreads; ++tid) {
-        // Set inSyscall so that the CPU doesn't squash when initially
+        // Set noSquashFromTC so that the CPU doesn't squash when initially
         // setting up registers.
-        thread[tid]->inSyscall = true;
+        thread[tid]->noSquashFromTC = true;
         // Initialise the ThreadContext's memory proxies
         thread[tid]->initMemProxies(thread[tid]->getTC());
     }
@@ -800,9 +800,9 @@ InOrderCPU::init()
         }
     }
 
-    // Clear inSyscall.
+    // Clear noSquashFromTC.
     for (ThreadID tid = 0; tid < numThreads; ++tid)
-        thread[tid]->inSyscall = false;
+        thread[tid]->noSquashFromTC = false;
 
     // Call Initializiation Routine for Resource Pool
     resPool->init();
diff --git a/src/cpu/inorder/inorder_dyn_inst.cc b/src/cpu/inorder/inorder_dyn_inst.cc
index 760c63948..dcf0ce6ae 100644
--- a/src/cpu/inorder/inorder_dyn_inst.cc
+++ b/src/cpu/inorder/inorder_dyn_inst.cc
@@ -220,12 +220,12 @@ InOrderDynInst::execute()
     // when using the TC during an instruction's execution
     // (specifically for instructions that have side-effects that use
     // the TC).  Fix this.
-    bool in_syscall = this->thread->inSyscall;
-    this->thread->inSyscall = true;
+    bool no_squash_from_TC = this->thread->noSquashFromTC;
+    this->thread->noSquashFromTC = true;
 
     this->fault = this->staticInst->execute(this, this->traceData);
 
-    this->thread->inSyscall = in_syscall;
+    this->thread->noSquashFromTC = no_squash_from_TC;
 
     return this->fault;
 }
@@ -244,12 +244,12 @@ InOrderDynInst::initiateAcc()
     // when using the TC during an instruction's execution
     // (specifically for instructions that have side-effects that use
     // the TC).  Fix this.
-    bool in_syscall = this->thread->inSyscall;
-    this->thread->inSyscall = true;
+    bool no_squash_from_TC = this->thread->noSquashFromTC;
+    this->thread->noSquashFromTC = true;
 
     this->fault = this->staticInst->initiateAcc(this, this->traceData);
 
-    this->thread->inSyscall = in_syscall;
+    this->thread->noSquashFromTC = no_squash_from_TC;
 
     return this->fault;
 }
diff --git a/src/cpu/inorder/thread_context.cc b/src/cpu/inorder/thread_context.cc
index 16ffd5b0f..b8662ef4c 100644
--- a/src/cpu/inorder/thread_context.cc
+++ b/src/cpu/inorder/thread_context.cc
@@ -90,10 +90,10 @@ InOrderThreadContext::takeOverFrom(ThreadContext *old_context)
     copyArchRegs(old_context);
 
     thread->funcExeInst = old_context->readFuncExeInst();
- 
+
     old_context->setStatus(ThreadContext::Halted);
 
-    thread->inSyscall = false;
+    thread->noSquashFromTC = false;
     thread->trapPending = false;
 }
 
@@ -159,7 +159,7 @@ InOrderThreadContext::serialize(std::ostream &os)
 void
 InOrderThreadContext::unserialize(Checkpoint *cp, const std::string &section)
 {
-    panic("unserialize unimplemented");    
+    panic("unserialize unimplemented");
 }
 
 
diff --git a/src/cpu/inorder/thread_state.hh b/src/cpu/inorder/thread_state.hh
index 34c146b42..4472bf1dd 100644
--- a/src/cpu/inorder/thread_state.hh
+++ b/src/cpu/inorder/thread_state.hh
@@ -61,10 +61,15 @@ class InOrderThreadState : public ThreadState {
     InOrderCPU *cpu;
 
   public:
-    /** Whether or not the thread is currently in syscall mode, and
-     * thus able to be externally updated without squashing.
+    /* This variable controls if writes to a thread context should cause a all
+     * dynamic/speculative state to be thrown away. Nominally this is the
+     * desired behavior because the external thread context write has updated
+     * some state that could be used by an inflight instruction, however there
+     * are some cases like in a fault/trap handler where this behavior would
+     * lead to successive restarts and forward progress couldn't be made. This
+     * variable controls if the squashing will occur.
      */
-    bool inSyscall;
+    bool noSquashFromTC;
 
     /** Whether or not the thread is currently waiting on a trap, and
      * thus able to be externally updated without squashing.
@@ -75,7 +80,8 @@ class InOrderThreadState : public ThreadState {
                        Process *_process)
         : ThreadState(reinterpret_cast<BaseCPU*>(_cpu), _thread_num,
                       _process),
-          cpu(_cpu), inSyscall(0), trapPending(0), lastGradIsBranch(false)
+          cpu(_cpu), noSquashFromTC(false), trapPending(false),
+          lastGradIsBranch(false)
     { }
 
     /** Handles the syscall. */