Changeset 44341 in webkit for trunk/JavaScriptCore/jit/ExecutableAllocator.h

Timestamp:

Jun 1, 2009, 6:20:35 PM (16 years ago)

Author:

[email protected]

Message:

2009-06-01 Gavin Barraclough <​[email protected]>

Reviewed by Sam "WX" Weinig.

Allow the JIT to operate without relying on use of RWX memory, on platforms where this is supported.

This patch adds a switch to Platform.h (ENABLE_ASSEMBLER_WX_EXCLUSIVE) which enables this mode of operation.
When this flag is set, all executable memory will be allocated RX, and switched to RW only whilst being
modified. Upon completion of code generation the protection is switched back to RX to allow execution.

Further optimization will be required before it is desirable to enable this mode of operation by default;
enabling this presently incurs a 5%-10% regression.

(Submitting disabled - no performance impact).

• assembler/AbstractMacroAssembler.h: (JSC::AbstractMacroAssembler::CodeLocationInstruction::repatchLoadToLEA): (JSC::AbstractMacroAssembler::CodeLocationLabel::fromFunctionPointer): (JSC::AbstractMacroAssembler::CodeLocationJump::relink): (JSC::AbstractMacroAssembler::CodeLocationCall::relink): (JSC::AbstractMacroAssembler::CodeLocationNearCall::relink): (JSC::AbstractMacroAssembler::CodeLocationDataLabel32::repatch): (JSC::AbstractMacroAssembler::CodeLocationDataLabelPtr::repatch): (JSC::AbstractMacroAssembler::ProcessorReturnAddress::relinkCallerToTrampoline): (JSC::AbstractMacroAssembler::ProcessorReturnAddress::relinkCallerToFunction): (JSC::AbstractMacroAssembler::ProcessorReturnAddress::relinkNearCallerToTrampoline): (JSC::AbstractMacroAssembler::ProcessorReturnAddress::relinkNearCallerToFunction): (JSC::AbstractMacroAssembler::PatchBuffer::PatchBuffer): (JSC::AbstractMacroAssembler::PatchBuffer::~PatchBuffer): (JSC::AbstractMacroAssembler::PatchBuffer::link): (JSC::AbstractMacroAssembler::PatchBuffer::patch): (JSC::AbstractMacroAssembler::PatchBuffer::performFinalization): (JSC::::CodeLocationCommon::nearCallAtOffset): (JSC::::CodeLocationCall::CodeLocationCall): (JSC::::CodeLocationNearCall::CodeLocationNearCall):
• assembler/AssemblerBuffer.h: (JSC::AssemblerBuffer::executableCopy):
• assembler/X86Assembler.h: (JSC::CAN_SIGN_EXTEND_U32_64): (JSC::X86Assembler::linkJump): (JSC::X86Assembler::linkCall): (JSC::X86Assembler::patchPointer): (JSC::X86Assembler::relinkJump): (JSC::X86Assembler::relinkCall): (JSC::X86Assembler::repatchInt32): (JSC::X86Assembler::repatchPointer): (JSC::X86Assembler::repatchLoadToLEA): (JSC::X86Assembler::patchInt32): (JSC::X86Assembler::patchRel32):
• jit/ExecutableAllocator.h: (JSC::ExecutableAllocator::): (JSC::ExecutableAllocator::makeWritable): (JSC::ExecutableAllocator::makeExecutable):
• jit/ExecutableAllocatorFixedVMPool.cpp: (JSC::FixedVMPoolAllocator::FixedVMPoolAllocator):
• jit/ExecutableAllocatorPosix.cpp: (JSC::ExecutablePool::systemAlloc): (JSC::ExecutablePool::systemRelease): (JSC::ExecutableAllocator::reprotectRegion):
• jit/ExecutableAllocatorWin.cpp:
• jit/JITPropertyAccess.cpp: (JSC::JIT::patchGetByIdSelf): (JSC::JIT::patchPutByIdReplace):
• wtf/Platform.h:

File:

• trunk/JavaScriptCore/jit/ExecutableAllocator.h (modified) (3 diffs)

trunk/JavaScriptCore/jit/ExecutableAllocator.h

@@ -37 +37 @@
 #define JIT_ALLOCATOR_LARGE_ALLOC_SIZE (ExecutableAllocator::pageSize * 4)
 
+#if ENABLE(ASSEMBLER_WX_EXCLUSIVE)
+#define PROTECTION_FLAGS_RW (PROT_READ | PROT_WRITE)
+#define PROTECTION_FLAGS_RX (PROT_READ | PROT_EXEC)
+#define INITIAL_PROTECTION_FLAGS PROTECTION_FLAGS_RX
+#else
+#define INITIAL_PROTECTION_FLAGS (PROT_READ | PROT_WRITE | PROT_EXEC)
+#endif
+
 namespace JSC {
 
@@ -113 +121 @@
 
 class ExecutableAllocator {
+    enum ProtectionSeting { Writable, Executable };
+
 public:
     static size_t pageSize;
@@ -142 +152 @@
     }
 
+#if ENABLE(ASSEMBLER_WX_EXCLUSIVE)
+    static void makeWritable(void* start, size_t size) { reprotectRegion(start, size, Writable); }
+    static void makeExecutable(void* start, size_t size) { reprotectRegion(start, size, Executable); }
+
+    class MakeWritable {
+    public:
+        MakeWritable(void* start, size_t size)
+            : m_start(start)
+            , m_size(size)
+        {
+            makeWritable(start, size);
+        }
+
+        ~MakeWritable()
+        {
+            makeExecutable(m_start, m_size);
+        }
+
+    private:
+        void* m_start;
+        size_t m_size;
+    };
+#else
+    static void makeWritable(void*, size_t) {}
+    static void makeExecutable(void*, size_t) {}
+    class MakeWritable { public: MakeWritable(void*, size_t) {} };
+#endif
+
 private:
+
+#if ENABLE(ASSEMBLER_WX_EXCLUSIVE)
+    static void reprotectRegion(void*, size_t, ProtectionSeting);
+#endif
+
     RefPtr<ExecutablePool> m_smallAllocationPool;
     static void intializePageSize();