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    Subject[tip:x86/asm] selftests/x86: Add syscall_nt selftest
    Commit-ID:  a9c909ce8c7853b4fc16055c50eb50d91e20cb93
    Gitweb: http://git.kernel.org/tip/a9c909ce8c7853b4fc16055c50eb50d91e20cb93
    Author: Andy Lutomirski <luto@kernel.org>
    AuthorDate: Mon, 17 Aug 2015 12:22:52 -0700
    Committer: Ingo Molnar <mingo@kernel.org>
    CommitDate: Tue, 18 Aug 2015 09:43:38 +0200

    selftests/x86: Add syscall_nt selftest

    I've had this sitting around for a while. Add it to the
    selftests tree. Far Cry running under Wine depends on this
    behavior.

    Signed-off-by: Andy Lutomirski <luto@kernel.org>
    Cc: Andy Lutomirski <luto@amacapital.net>
    Cc: Borislav Petkov <bp@alien8.de>
    Cc: Brian Gerst <brgerst@gmail.com>
    Cc: Denys Vlasenko <dvlasenk@redhat.com>
    Cc: H. Peter Anvin <hpa@zytor.com>
    Cc: Linus Torvalds <torvalds@linux-foundation.org>
    Cc: Peter Zijlstra <peterz@infradead.org>
    Cc: Shuah Khan <shuahkh@osg.samsung.com>
    Cc: Thomas Gleixner <tglx@linutronix.de>
    Link: http://lkml.kernel.org/r/ee4d63799a9e5294b70930618b71d04d2770eb2d.1439838962.git.luto@kernel.org
    Signed-off-by: Ingo Molnar <mingo@kernel.org>
    ---
    tools/testing/selftests/x86/Makefile | 2 +-
    tools/testing/selftests/x86/syscall_nt.c | 54 ++++++++++++++++++++++++++++++++
    2 files changed, 55 insertions(+), 1 deletion(-)

    diff --git a/tools/testing/selftests/x86/Makefile b/tools/testing/selftests/x86/Makefile
    index 986e7cb..29089b2 100644
    --- a/tools/testing/selftests/x86/Makefile
    +++ b/tools/testing/selftests/x86/Makefile
    @@ -4,7 +4,7 @@ include ../lib.mk

    .PHONY: all all_32 all_64 warn_32bit_failure clean

    -TARGETS_C_BOTHBITS := single_step_syscall sysret_ss_attrs ldt_gdt
    +TARGETS_C_BOTHBITS := single_step_syscall sysret_ss_attrs ldt_gdt syscall_nt
    TARGETS_C_32BIT_ONLY := entry_from_vm86 syscall_arg_fault sigreturn

    TARGETS_C_32BIT_ALL := $(TARGETS_C_BOTHBITS) $(TARGETS_C_32BIT_ONLY)
    diff --git a/tools/testing/selftests/x86/syscall_nt.c b/tools/testing/selftests/x86/syscall_nt.c
    new file mode 100644
    index 0000000..60c06af4
    --- /dev/null
    +++ b/tools/testing/selftests/x86/syscall_nt.c
    @@ -0,0 +1,54 @@
    +/*
    + * syscall_nt.c - checks syscalls with NT set
    + * Copyright (c) 2014-2015 Andrew Lutomirski
    + *
    + * This program is free software; you can redistribute it and/or modify
    + * it under the terms and conditions of the GNU General Public License,
    + * version 2, as published by the Free Software Foundation.
    + *
    + * This program is distributed in the hope it will be useful, but
    + * WITHOUT ANY WARRANTY; without even the implied warranty of
    + * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
    + * General Public License for more details.
    + *
    + * Some obscure user-space code requires the ability to make system calls
    + * with FLAGS.NT set. Make sure it works.
    + */
    +
    +#include <stdio.h>
    +#include <unistd.h>
    +#include <sys/syscall.h>
    +#include <asm/processor-flags.h>
    +
    +#ifdef __x86_64__
    +# define WIDTH "q"
    +#else
    +# define WIDTH "l"
    +#endif
    +
    +static unsigned long get_eflags(void)
    +{
    + unsigned long eflags;
    + asm volatile ("pushf" WIDTH "\n\tpop" WIDTH " %0" : "=rm" (eflags));
    + return eflags;
    +}
    +
    +static void set_eflags(unsigned long eflags)
    +{
    + asm volatile ("push" WIDTH " %0\n\tpopf" WIDTH
    + : : "rm" (eflags) : "flags");
    +}
    +
    +int main()
    +{
    + printf("[RUN]\tSet NT and issue a syscall\n");
    + set_eflags(get_eflags() | X86_EFLAGS_NT);
    + syscall(SYS_getpid);
    + if (get_eflags() & X86_EFLAGS_NT) {
    + printf("[OK]\tThe syscall worked and NT is still set\n");
    + return 0;
    + } else {
    + printf("[FAIL]\tThe syscall worked but NT was cleared\n");
    + return 1;
    + }
    +}

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