llvm-project

8403d52d - [SystemZ][z/OS] Support naked functions as XPLINK stubs (#239862)

[SystemZ][z/OS] Support naked functions as XPLINK stubs (#239862) A function with the `naked` attribute has no prologue or epilogue. On z/OS XPLINK it maps to a stub function, which has a stub entry marker instead of the normal entry point marker and has no PPA1. AsmPrinter: * For naked functions, emitFunctionEntryLabel() no longer calls calculatePPA1() and no longer emits the 16-byte entry point marker. It emits an 8-byte stub marker (eyecatcher 0x00C300C500C500, mark type C'4'), preceded by 8 bytes of zero padding. The padding keeps the entry point at function start + 16, the same offset as for a normal function. * emitFunctionBodyEnd() returns early for naked functions. Otherwise it would use DeferredPPA1.back(), which is the previous function's entry or an empty vector. ISel: * LowerFormalArguments() is not called for naked functions, so the ADA virtual register (R5 on entry) was never created. Globals and internal callees in a stub then used an invalid register. Add getOrCreateADAVirtualRegister(), which creates the live-in on first use, and use it in LowerFormalArguments(), getADAEntry() and getzOSCalleeAndADA(). A naked function that does not touch the ADA gets no live-in. As on Linux on Z, the backend does not diagnose stack objects, spills or frame-requiring calls in a naked function. This is the user's contract, and Clang already restricts naked function bodies to inline asm. Add zos-naked.ll to test the stub marker, the padding, neighbouring normal functions, ADA access from a stub, and the interaction with minsize/optsize and "frame-pointer". Assisted by: IBM Bob