Changeset 232215 in webkit

Timestamp:

May 25, 2018 4:45:36 PM (6 years ago)

Author:

mark.lam@apple.com

Message:

MachineContext's instructionPointer() should handle null PCs correctly.
​https://bugs.webkit.org/show_bug.cgi?id=186004
<rdar://problem/40570067>

Reviewed by Saam Barati.

instructionPointer() returns a MacroAssemblerCodePtr<CFunctionPtrTag>. However,
MacroAssemblerCodePtr's constructor does not accept a null pointer value and will
assert accordingly with a debug ASSERT. This is inconsequential for release
builds, but to avoid this assertion failure, we should check for a null PC and
return MacroAssemblerCodePtr<CFunctionPtrTag>(nullptr) instead (which uses the
MacroAssemblerCodePtr(std::nullptr_t) version of the constructor instead).

Alternatively, we can change all of MacroAssemblerCodePtr's constructors to check
for null pointers, but I rather not do that yet. In general,
MacroAssemblerCodePtrs are constructed with non-null pointers, and I prefer to
leave it that way for now.

Note: this assertion failure only manifests when we have signal traps enabled,
and encounter a null pointer deref.

• runtime/MachineContext.h:

(JSC::MachineContext::instructionPointer):

Location:

trunk/Source/JavaScriptCore

Files:

• ChangeLog (modified) (1 diff)
• runtime/MachineContext.h (modified) (1 diff)

trunk/Source/JavaScriptCore/ChangeLog

@@ +1 @@
+2018-05-25  Mark Lam  <mark.lam@apple.com>
+
+        MachineContext's instructionPointer() should handle null PCs correctly.
+        https://bugs.webkit.org/show_bug.cgi?id=186004
+        <rdar://problem/40570067>
+
+        Reviewed by Saam Barati.
+
+        instructionPointer() returns a MacroAssemblerCodePtr<CFunctionPtrTag>.  However,
+        MacroAssemblerCodePtr's constructor does not accept a null pointer value and will
+        assert accordingly with a debug ASSERT.  This is inconsequential for release
+        builds, but to avoid this assertion failure, we should check for a null PC and
+        return MacroAssemblerCodePtr<CFunctionPtrTag>(nullptr) instead (which uses the
+        MacroAssemblerCodePtr(std::nullptr_t) version of the constructor instead).
+
+        Alternatively, we can change all of MacroAssemblerCodePtr's constructors to check
+        for null pointers, but I rather not do that yet.  In general,
+        MacroAssemblerCodePtrs are constructed with non-null pointers, and I prefer to
+        leave it that way for now.
+
+        Note: this assertion failure only manifests when we have signal traps enabled,
+        and encounter a null pointer deref.
+
+        * runtime/MachineContext.h:
+        (JSC::MachineContext::instructionPointer):
+
 2018-05-25  Mark Lam  <mark.lam@apple.com>
 

trunk/Source/JavaScriptCore/runtime/MachineContext.h

@@ -439 +439 @@
     void* value = instructionPointerImpl(const_cast<PlatformRegisters&>(regs));
 #endif
+    if (!value)
+        return MacroAssemblerCodePtr<CFunctionPtrTag>(nullptr);
     return MacroAssemblerCodePtr<CFunctionPtrTag>(value);
 }