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    Merge branch 'x86-asm-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip · b0c79f49
    Linus Torvalds authored
    Pull x86 asm updates from Ingo Molnar:
    
     - Introduce the ORC unwinder, which can be enabled via
       CONFIG_ORC_UNWINDER=y.
    
       The ORC unwinder is a lightweight, Linux kernel specific debuginfo
       implementation, which aims to be DWARF done right for unwinding.
       Objtool is used to generate the ORC unwinder tables during build, so
       the data format is flexible and kernel internal: there's no
       dependency on debuginfo created by an external toolchain.
    
       The ORC unwinder is almost two orders of magnitude faster than the
       (out of tree) DWARF unwinder - which is important for perf call graph
       profiling. It is also significantly simpler and is coded defensively:
       there has not been a single ORC related kernel crash so far, even
       with early versions. (knock on wood!)
    
       But the main advantage is that enabling the ORC unwinder allows
       CONFIG_FRAME_POINTERS to be turned off - which speeds up the kernel
       measurably:
    
       With frame pointers disabled, GCC does not have to add frame pointer
       instrumentation code to every function in the kernel. The kernel's
       .text size decreases by about 3.2%, resulting in better cache
       utilization and fewer instructions executed, resulting in a broad
       kernel-wide speedup. Average speedup of system calls should be
       roughly in the 1-3% range - measurements by Mel Gorman [1] have shown
       a speedup of 5-10% for some function execution intense workloads.
    
       The main cost of the unwinder is that the unwinder data has to be
       stored in RAM: the memory cost is 2-4MB of RAM, depending on kernel
       config - which is a modest cost on modern x86 systems.
    
       Given how young the ORC unwinder code is it's not enabled by default
       - but given the performance advantages the plan is to eventually make
       it the default unwinder on x86.
    
       See Documentation/x86/orc-unwinder.txt for more details.
    
     - Remove lguest support: its intended role was that of a temporary
       proof of concept for virtualization, plus its removal will enable the
       reduction (removal) of the paravirt API as well, so Rusty agreed to
       its removal. (Juergen Gross)
    
     - Clean up and fix FSGS related functionality (Andy Lutomirski)
    
     - Clean up IO access APIs (Andy Shevchenko)
    
     - Enhance the symbol namespace (Jiri Slaby)
    
    * 'x86-asm-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip: (47 commits)
      objtool: Handle GCC stack pointer adjustment bug
      x86/entry/64: Use ENTRY() instead of ALIGN+GLOBAL for stub32_clone()
      x86/fpu/math-emu: Add ENDPROC to functions
      x86/boot/64: Extract efi_pe_entry() from startup_64()
      x86/boot/32: Extract efi_pe_entry() from startup_32()
      x86/lguest: Remove lguest support
      x86/paravirt/xen: Remove xen_patch()
      objtool: Fix objtool fallthrough detection with function padding
      x86/xen/64: Fix the reported SS and CS in SYSCALL
      objtool: Track DRAP separately from callee-saved registers
      objtool: Fix validate_branch() return codes
      x86: Clarify/fix no-op barriers for text_poke_bp()
      x86/switch_to/64: Rewrite FS/GS switching yet again to fix AMD CPUs
      selftests/x86/fsgsbase: Test selectors 1, 2, and 3
      x86/fsgsbase/64: Report FSBASE and GSBASE correctly in core dumps
      x86/fsgsbase/64: Fully initialize FS and GS state in start_thread_common
      x86/asm: Fix UNWIND_HINT_REGS macro for older binutils
      x86/asm/32: Fix regs_get_register() on segment registers
      x86/xen/64: Rearrange the SYSCALL entries
      x86/asm/32: Remove a bunch of '& 0xffff' from pt_regs segment reads
      ...
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