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Ryan Houdek
c75778abeb
When running on a system with a 48-bit VA, if FEX does any allocations between us reserving the upper 128TB and the application running, then /technically/ we are intersecting with the application's memory region in the lower 47-bits. This didn't typically result in any problems due to how ASLR works, but if we did any large allocations (like #4291 wants with 128MB VMA region) then these typically get pushed higher in the VA space. Again not usually a problem, but if you happen to be running an application that is using MAP_FIXED with hardcoded addresses then this can stomp over FEX-Emu memory causing problems. This is what happens with Wine, it reserves the upper-32MB of its 47-bit VA space, which is /highly/ likely to stomp on FEX memory. In-fact it likely occurs all the time, we just got lucky with whatever it was clobbering wasn't used at the time. On 39-bit VA systems this isn't a problem because the mmap fails outright with a warning message from WINE. Because we are already reserving the upper 128TB of VA space, instead just always enable our allocator and use the regions that were reserved. We need to be a little bit careful to ensure we don't accidentally allocate more memory post-reservation but that just requires a small adjustment to our unique_ptr and constructor for the 64BitAllocator. This means /all/ FEX-Emu allocations will be in the upper 128TB VA space when running 64-bit applications on a 48-bit VA system. Which is kind of nice. Fixes WINE in #4291 when the allocator stats are bumped to 128MB per process.
FEXCore - Fast x86 Core emulation library
This is the core emulation library that is used for the FEX emulator project. This project aims to provide a fast and functional x86-64 emulation library that can meet and surpass other x86-64 emulation libraries.
Goals
- Be as fast as possible, beating and exceeding current options for x86-64 emulation
- 25% - 50% lower performance than native code would be desired target
- Use an IR to efficiently translate x86-64 to our host architecture
- Support a tiered recompiler to allow for fast runtime performance
- Support offline compilation and offline tooling for inspection and performance analysis
- Support threaded emulation. Including emulating x86-64's strong memory model on weak memory model architectures
- Support a significant portion of the x86-64 instruction space.
- Including MMX, SSE, SSE2, SSE3, SSSE3, and SSE4*
- Support fallback routines for uncommonly used x86-64 instructions
- Including x87 and 3DNow!
- Only support userspace emulation.
- All x86-64 instructions run as if they are under CPL-3(userland) security layer
- Minimal Linux Syscall emulation for testing purposes
- Portable library implementation in order to support easy integration in to applications
Target Host Architecture
The target host architecture for this library is AArch64. Specifically the ARMv8.1 version or newer. The CPU IR is designed with AArch64 in mind but should allow for other architectures as well. x86-64 host support is available for ease of development, but is not a priority.
Not desired
- Kernel space emulation
- CPL0-2 emulation
- Real Mode, Protected Mode, Virtual-8086 Mode, System Management Mode
- IRQs
- SVM
- "Cycle Accurate" emulation