Fix crash with JIT on x86

The stack must be 16-byte aligned in order for compiler generated
alignment requiring SSE instructions to work on the stack. For x86 the
stack upon entry is 4 bytes off due to the saved eip. Then another 20
bytes for the saved registers (ebp, eax, ebx, etc.). That means we have
to add another 8 bytes to reach the next 16-byte alignment.

Change-Id: Ifde49a89224a129f8307fff3713563b80772cff1
Task-number: QTBUG-66773
Reviewed-by: Lars Knoll <lars.knoll@qt.io>

1 files changed, 4 insertions, 0 deletions

diff --git a/src/qml/jit/qv4assembler.cpp b/src/qml/jit/qv4assembler.cpp
index 72b057b2bc..c3e16c4093 100644
--- a/src/qml/jit/qv4assembler.cpp
+++ b/src/qml/jit/qv4assembler.cpp
@@ -276,12 +276,16 @@ struct PlatformAssembler_X86_All : JSC::MacroAssembler<JSC::MacroAssemblerX86>
         push(JSStackFrameRegister);
         push(CppStackFrameRegister);
         push(EngineRegister);
+        // Ensure the stack is 16-byte aligned in order for compiler generated aligned SSE2
+        // instructions to be able to target the stack.
+        subPtr(TrustedImm32(8), StackPointerRegister);
         loadPtr(Address(FramePointerRegister, 2 * PointerSize), CppStackFrameRegister);
         loadPtr(Address(FramePointerRegister, 3 * PointerSize), EngineRegister);
     }
 
     void generatePlatformFunctionExit()
     {
+        addPtr(TrustedImm32(8), StackPointerRegister);
         pop(EngineRegister);
         pop(CppStackFrameRegister);
         pop(JSStackFrameRegister);