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    Subject[PATCH v2 00/36] x86: Rewrite all syscall entries except native 64-bit
    Date
    The first two patches are optimizations that I'm surprised we didn't
    already have. I noticed them when I was looking at the generated
    asm.

    The next two patches are tests and some old stuff. There's a test
    that validates the vDSO AT_SYSINFO annotations. There's also a test
    that exercises some assumptions that signal handling and ptracers
    make about syscalls that currently do *not* hold on 64-bit AMD using
    32-bit AT_SYSINFO.

    The next three patches are NT cleanups and a lockdep cleanup.

    It may pay to apply the beginning of the series (at most through
    "x86/entry/64/compat: After SYSENTER, move STI after the NT fixup")
    without waiting for everyone to wrap their heads around the rest.

    The rest is basically a rewrite of syscalls for all cases except
    64-bit native. With these patches applied, there is a single 32-bit
    vDSO and it uses SYSCALL, SYSENTER, and INT80 almost interchangeably
    via alternatives. The semantics of SYSENTER and SYSCALL are defined
    as:

    1. If SYSCALL, ESP = ECX
    2. ECX = *ESP
    3. IP = INT80 landing pad
    4. Opportunistic SYSRET/SYSEXIT is enabled on return

    The vDSO is rearranged so that these semantics work. Anything that
    backs IP up by 2 ends up pointing at a bona fide int $0x80
    instruction with the expected regs.

    In the process, the vDSO CFI annotations (which are actually used)
    get rewritten using normal CFI directives.

    Opportunistic SYSRET/SYSEXIT only happens on return when CS and SS
    are as expected, IP points to the INT80 landing pad, and flags are
    in good shape. (There is no longer any assumption that full
    fast-path 32-bit syscalls don't muck with the registers that matter
    for fast exits -- I played with maintaining an optimization like
    that with poor results. I may try again if it saves a few cycles.)

    Other than that, the system call entries are simplified to the bare
    minimum prologue and a call to a C function. Amusingly, SYSENTER
    and SYSCALL32 use the same C function.

    To make that work, I had to remove all the 32-bit syscall stubs
    except the clone argument hack. This is because, for C code to call
    through the system call table, the system call table entries need to
    be real function pointers with C-compatible ABIs.

    There is nothing at all anymore that requires that x86_32 syscalls
    be asmlinkage. That could be removed in a subsequent patch.

    The upshot appears to be a ~16 cycle performance hit on 32-bit fast
    path syscalls. (On my system, my little prctl test takes 172 cycles
    before and 188 cycles with these patches applied.)

    The slow path is probably faster under most circumstances and, if
    the exit slow path gets hit, it'll be much faster because (as we
    already do in the 64-bit native case) we can still use
    SYSEXIT/SYSRET.

    The patchset is structured as a removal of the old fast syscall
    code, then the change that makes syscalls into real functions, then
    a clean re-implementation of fast syscalls.

    If we want some of the 25 cycles back, we could consider open-coding
    a new C fast path.

    Changes from v1:
    - The unwind_vdso_32 test now warns on broken Debian installations
    instead of failing. The problem is now fully understood, will
    be fixed by Debian and possibly also fixed by upstream glibc.
    - execve was rather broken in v1.
    - It's quite a bit faster now (the optimizations at the end are mostly new).
    - int80 on 64-bit no longer clobbers extra regs (thanks Denys!).
    - The uaccess stuff is new.
    - Lots of other things that I forgot, I'm sure.

    Andy Lutomirski (36):
    x86/uaccess: Tell the compiler that uaccess is unlikely to fault
    x86/uaccess: __chk_range_not_ok is unlikely to return true
    selftests/x86: Add a test for vDSO unwinding
    selftests/x86: Add a test for syscall restart and arg modification
    x86/entry/64/compat: Fix SYSENTER's NT flag before user memory access
    x86/entry: Move lockdep_sys_exit to prepare_exit_to_usermode
    x86/entry/64/compat: After SYSENTER, move STI after the NT fixup
    x86/vdso: Remove runtime 32-bit vDSO selection
    x86/asm: Re-add manual CFI infrastructure
    x86/vdso: Define BUILD_VDSO while building and emit .eh_frame in asm
    x86/vdso: Replace hex int80 CFI annotations with gas directives
    x86/elf/64: Clear more registers in elf_common_init
    x86/vdso/32: Save extra registers in the INT80 vsyscall path
    x86/entry/64/compat: Disable SYSENTER and SYSCALL32 entries
    x86/entry/64/compat: Remove audit optimizations
    x86/entry/64/compat: Remove most of the fast system call machinery
    x86/entry/64/compat: Set up full pt_regs for all compat syscalls
    x86/entry/syscalls: Move syscall table declarations into
    asm/syscalls.h
    x86/syscalls: Give sys_call_ptr_t a useful type
    x86/entry: Add do_syscall_32, a C function to do 32-bit syscalls
    x86/entry/64/compat: Migrate the body of the syscall entry to C
    x86/entry: Add C code for fast system call entries
    x86/vdso/compat: Wire up SYSENTER and SYSCSALL for compat userspace
    x86/entry/compat: Implement opportunistic SYSRETL for compat syscalls
    x86/entry/32: Open-code return tracking from fork and kthreads
    x86/entry/32: Switch INT80 to the new C syscall path
    x86/entry/32: Re-implement SYSENTER using the new C path
    x86/asm: Remove thread_info.sysenter_return
    x86/entry: Remove unnecessary IRQ twiddling in fast 32-bit syscalls
    x86/entry: Make irqs_disabled checks in exit code depend on lockdep
    x86/entry: Force inlining of 32-bit syscall code
    x86/entry: Micro-optimize compat fast syscall arg fetch
    x86/entry: Hide two syscall entry assertions behind CONFIG_DEBUG_ENTRY
    x86/entry: Use pt_regs_to_thread_info() in syscall entry tracing
    x86/entry: Split and inline prepare_exit_to_usermode
    x86/entry: Split and inline syscall_return_slowpath

    arch/x86/Makefile | 10 +-
    arch/x86/entry/common.c | 255 ++++++++--
    arch/x86/entry/entry_32.S | 184 +++----
    arch/x86/entry/entry_64.S | 9 +-
    arch/x86/entry/entry_64_compat.S | 541 +++++----------------
    arch/x86/entry/syscall_32.c | 9 +-
    arch/x86/entry/syscall_64.c | 4 +-
    arch/x86/entry/syscalls/syscall_32.tbl | 12 +-
    arch/x86/entry/vdso/Makefile | 39 +-
    arch/x86/entry/vdso/vdso2c.c | 2 +-
    arch/x86/entry/vdso/vdso32-setup.c | 28 +-
    arch/x86/entry/vdso/vdso32/int80.S | 56 ---
    arch/x86/entry/vdso/vdso32/syscall.S | 75 ---
    arch/x86/entry/vdso/vdso32/sysenter.S | 116 -----
    arch/x86/entry/vdso/vdso32/system_call.S | 57 +++
    arch/x86/entry/vdso/vma.c | 13 +-
    arch/x86/ia32/ia32_signal.c | 4 +-
    arch/x86/include/asm/dwarf2.h | 177 +++++++
    arch/x86/include/asm/elf.h | 10 +-
    arch/x86/include/asm/syscall.h | 14 +-
    arch/x86/include/asm/thread_info.h | 1 -
    arch/x86/include/asm/uaccess.h | 14 +-
    arch/x86/include/asm/vdso.h | 10 +-
    arch/x86/kernel/asm-offsets.c | 3 -
    arch/x86/kernel/signal.c | 4 +-
    arch/x86/um/sys_call_table_32.c | 7 +-
    arch/x86/um/sys_call_table_64.c | 7 +-
    arch/x86/xen/setup.c | 13 +-
    tools/testing/selftests/x86/Makefile | 5 +-
    tools/testing/selftests/x86/ptrace_syscall.c | 294 +++++++++++
    .../testing/selftests/x86/raw_syscall_helper_32.S | 46 ++
    tools/testing/selftests/x86/unwind_vdso.c | 209 ++++++++
    32 files changed, 1258 insertions(+), 970 deletions(-)
    delete mode 100644 arch/x86/entry/vdso/vdso32/int80.S
    delete mode 100644 arch/x86/entry/vdso/vdso32/syscall.S
    delete mode 100644 arch/x86/entry/vdso/vdso32/sysenter.S
    create mode 100644 arch/x86/entry/vdso/vdso32/system_call.S
    create mode 100644 arch/x86/include/asm/dwarf2.h
    create mode 100644 tools/testing/selftests/x86/ptrace_syscall.c
    create mode 100644 tools/testing/selftests/x86/raw_syscall_helper_32.S
    create mode 100644 tools/testing/selftests/x86/unwind_vdso.c

    --
    2.4.3



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