#12736: Calling a complex Haskell function (obtained via FFI wrapper function) from MSVC 64-bit C code (passed in as FunPtr) can leave SSE2 registers in the XMM6-XMM15 range modified -------------------------------------+------------------------------------- Reporter: bavism | Owner: Type: bug | Status: new Priority: normal | Milestone: Component: Compiler (FFI) | Version: 7.10.3 Resolution: | Keywords: | ffi,registers,sse2,clobber,xmm Operating System: Windows | Architecture: x86_64 | (amd64) Type of failure: Incorrect result | Test Case: at runtime | https://github.com/bavis-m/raycast Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Comment (by bavism): Replying to [comment:1 carter]:
Reading the doc {{{ XMM6:XMM15, YMM6:YMM15 Nonvolatile (XMM), Volatile (upper half of YMM) Must be preserved as needed by callee. YMM registers must be preserved as needed by caller.
}}}
It looks like if you have the callee clobber ymm6-16 you can get the caller to handle the save / restore Alternatively, a simple wrapper around the Haskell functions could explicitly read xmm6-16 before entering the Haskell call and set the values after return. So that should at least fix it with a simple read call and set sequence on the c side
That said, sounds like this indeed a bug, though the xmm vs ymm caller vs callee stuff is kinda gross and definitely a bug in the wrappers/stubs generated for the windows platform.
Please share if the near term work around helps. I realize it adds an extra indirection in the Haskell call, but probably simplest way to fix it this week?
Turns out this was much more difficult than I initially anticipated, as MSVC does not allow inline assembly in x64 projects :(. I have pushed up a workaround to a new branch in that project, {{{fixasm}}}, that directs Visual Studio to build a new file, stub.asm, which exposes a stub function for calling a Haskell function pointer. The stub function saves XMM6-XMM15. This causes the Haskell function to not clobber the registers, and everything works correctly. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/12736#comment:3 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler