Changeset 157609 in webkit

Timestamp:

Oct 17, 2013, 4:00:25 PM (13 years ago)

Author:

ggaren@apple.com

Message:

Eliminate uses of JITSTACKFRAME_ARGS_INDEX as scratch area for thunks
​https://bugs.webkit.org/show_bug.cgi?id=122973

Reviewed by Michael Saboff.

• jit/ThunkGenerators.cpp:

(JSC::throwExceptionFromCallSlowPathGenerator): This was all dead code,
so I removed it.

The code acted as if it needed to pass an argument to
lookupExceptionHandler, and as if it passed that argument to itself
through JITStackFrame. However, lookupExceptionHandler does not take
an argument (other than the default ExecState argument), and the code
did not initialize the thing that it thought it passed to itself!

Location:

trunk/Source/JavaScriptCore

Files:

• ChangeLog (modified) (1 diff)
• jit/ThunkGenerators.cpp (modified) (4 diffs)

trunk/Source/JavaScriptCore/ChangeLog

@@ +1 @@
+2013-10-17  Geoffrey Garen  <ggaren@apple.com>
+
+        Eliminate uses of JITSTACKFRAME_ARGS_INDEX as scratch area for thunks
+        https://bugs.webkit.org/show_bug.cgi?id=122973
+
+        Reviewed by Michael Saboff.
+
+        * jit/ThunkGenerators.cpp:
+        (JSC::throwExceptionFromCallSlowPathGenerator): This was all dead code,
+        so I removed it.
+
+        The code acted as if it needed to pass an argument to
+        lookupExceptionHandler, and as if it passed that argument to itself
+        through JITStackFrame. However, lookupExceptionHandler does not take
+        an argument (other than the default ExecState argument), and the code
+        did not initialize the thing that it thought it passed to itself!
+
 2013-10-17  Alex Christensen  <achristensen@webkit.org>
 

trunk/Source/JavaScriptCore/jit/ThunkGenerators.cpp

@@ -57 +57 @@
 }
 
+// We will jump here if the JIT code tries to make a call, but the
+// linking helper (C++ code) decides to throw an exception instead.
 MacroAssemblerCodeRef throwExceptionFromCallSlowPathGenerator(VM* vm)
 {
     CCallHelpers jit(vm);
     
-    // We will jump to here if the JIT code thinks it's making a call, but the
-    // linking helper (C++ code) decided to throw an exception instead. We will
-    // have saved the callReturnIndex in the first arguments of JITStackFrame.
-    // Note that the return address will be on the stack at this point, so we
-    // need to remove it and drop it on the floor, since we don't care about it.
-    // Finally note that the call frame register points at the callee frame, so
-    // we need to pop it.
+    // The call pushed a return address, so we need to pop it back off to re-align the stack,
+    // even though we won't use it.
     jit.preserveReturnAddressAfterCall(GPRInfo::nonPreservedNonReturnGPR);
+
+    // The CallFrame register points to the (failed) callee frame, so we need to pop back one frame.
     jit.loadPtr(
         CCallHelpers::Address(
@@ -74 +73 @@
             static_cast<ptrdiff_t>(sizeof(Register)) * JSStack::CallerFrame),
         GPRInfo::callFrameRegister);
-#if USE(JSVALUE64)
-    jit.peek64(GPRInfo::nonPreservedNonReturnGPR, JITSTACKFRAME_ARGS_INDEX);
-#else
-    jit.peek(GPRInfo::nonPreservedNonReturnGPR, JITSTACKFRAME_ARGS_INDEX);
-#endif
-    jit.setupArgumentsWithExecState(GPRInfo::nonPreservedNonReturnGPR);
+
+    jit.setupArgumentsExecState();
     jit.move(CCallHelpers::TrustedImmPtr(bitwise_cast<void*>(lookupExceptionHandler)), GPRInfo::nonArgGPR0);
     emitPointerValidation(jit, GPRInfo::nonArgGPR0);
@@ -101 +96 @@
             static_cast<ptrdiff_t>(sizeof(Register)) * JSStack::ReturnPC));
     jit.storePtr(GPRInfo::callFrameRegister, &vm->topCallFrame);
-#if USE(JSVALUE64)
-    jit.poke64(GPRInfo::nonPreservedNonReturnGPR, JITSTACKFRAME_ARGS_INDEX);
-#else
-    jit.poke(GPRInfo::nonPreservedNonReturnGPR, JITSTACKFRAME_ARGS_INDEX);
-#endif
     jit.setupArgumentsExecState();
     jit.move(CCallHelpers::TrustedImmPtr(bitwise_cast<void*>(slowPathFunction)), GPRInfo::nonArgGPR0);
@@ -137 +127 @@
     // save the return address to the call frame while we make a C++ function call
     // to perform linking and lazy compilation if necessary. We expect the callee
-    // to be in nonArgGPR0/nonArgGPR1 (payload/tag), the call frame to have already
-    // been adjusted, nonPreservedNonReturnGPR holds the exception handler index,
-    // and all other registers to be available for use. We use JITStackFrame::args
-    // to save important information across calls.
+    // to be in nonArgGPR0/nonArgGPR1 (payload/tag), the CallFrame to have already
+    // been adjusted, and all other registers to be available for use.
     
     CCallHelpers jit(vm);