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    Subject[PATCH 19/23] tracehook: asm/syscall.h
    Date
    This adds asm-generic/syscall.h, which documents what a real
    asm-ARCH/syscall.h file should define. This is not used yet,
    but will provide all the machine-dependent details of examining
    a user system call about to begin, in progress, or just ended.

    Each arch should add an asm-ARCH/syscall.h that defines all the
    entry points documented in asm-generic/syscall.h, as short inlines
    if possible. This lets us write new tracing code that understands
    user system call registers, without any new arch-specific work.

    Signed-off-by: Roland McGrath <roland@redhat.com>
    ---
    include/asm-generic/syscall.h | 141 +++++++++++++++++++++++++++++++++++++++++
    include/linux/tracehook.h | 3 +-
    2 files changed, 143 insertions(+), 1 deletions(-)

    diff --git a/include/asm-generic/syscall.h b/include/asm-generic/syscall.h
    new file mode 100644
    index 0000000..abcf34c
    --- /dev/null
    +++ b/include/asm-generic/syscall.h
    @@ -0,0 +1,141 @@
    +/*
    + * Access to user system call parameters and results
    + *
    + * Copyright (C) 2008 Red Hat, Inc. All rights reserved.
    + *
    + * This copyrighted material is made available to anyone wishing to use,
    + * modify, copy, or redistribute it subject to the terms and conditions
    + * of the GNU General Public License v.2.
    + *
    + * This file is a stub providing documentation for what functions
    + * asm-ARCH/syscall.h files need to define. Most arch definitions
    + * will be simple inlines.
    + *
    + * All of these functions expect to be called with no locks,
    + * and only when the caller is sure that the task of interest
    + * cannot return to user mode while we are looking at it.
    + */
    +
    +#ifndef _ASM_SYSCALL_H
    +#define _ASM_SYSCALL_H 1
    +
    +struct task_struct;
    +struct pt_regs;
    +
    +/**
    + * syscall_get_nr - find what system call a task is executing
    + * @task: task of interest, must be blocked
    + * @regs: task_pt_regs() of @task
    + *
    + * If @task is executing a system call or is at system call
    + * tracing about to attempt one, returns the system call number.
    + * If @task is not executing a system call, i.e. it's blocked
    + * inside the kernel for a fault or signal, returns -1.
    + *
    + * It's only valid to call this when @task is known to be blocked.
    + */
    +long syscall_get_nr(struct task_struct *task, struct pt_regs *regs);
    +
    +/**
    + * syscall_rollback - roll back registers after an aborted system call
    + * @task: task of interest, must be in system call exit tracing
    + * @regs: task_pt_regs() of @task
    + *
    + * It's only valid to call this when @task is stopped for system
    + * call exit tracing (due to TIF_SYSCALL_TRACE or TIF_SYSCALL_AUDIT),
    + * after tracehook_report_syscall_entry() returned nonzero to prevent
    + * the system call from taking place.
    + *
    + * This rolls back the register state in @regs so it's as if the
    + * system call instruction was a no-op. The registers containing
    + * the system call number and arguments are as they were before the
    + * system call instruction. This may not be the same as what the
    + * register state looked like at system call entry tracing.
    + */
    +void syscall_rollback(struct task_struct *task, struct pt_regs *regs);
    +
    +/**
    + * syscall_get_error - check result of traced system call
    + * @task: task of interest, must be blocked
    + * @regs: task_pt_regs() of @task
    + *
    + * Returns 0 if the system call succeeded, or -ERRORCODE if it failed.
    + *
    + * It's only valid to call this when @task is stopped for tracing on exit
    + * from a system call, due to %TIF_SYSCALL_TRACE or %TIF_SYSCALL_AUDIT.
    + */
    +long syscall_get_error(struct task_struct *task, struct pt_regs *regs);
    +
    +/**
    + * syscall_get_return_value - get the return value of a traced system call
    + * @task: task of interest, must be blocked
    + * @regs: task_pt_regs() of @task
    + *
    + * Returns the return value of the successful system call.
    + * This value is meaningless if syscall_get_error() returned nonzero.
    + *
    + * It's only valid to call this when @task is stopped for tracing on exit
    + * from a system call, due to %TIF_SYSCALL_TRACE or %TIF_SYSCALL_AUDIT.
    + */
    +long syscall_get_return_value(struct task_struct *task, struct pt_regs *regs);
    +
    +/**
    + * syscall_set_return_value - change the return value of a traced system call
    + * @task: task of interest, must be blocked
    + * @regs: task_pt_regs() of @task
    + * @error: negative error code, or zero to indicate success
    + * @val: user return value if @error is zero
    + *
    + * This changes the results of the system call that user mode will see.
    + * If @error is zero, the user sees a successful system call with a
    + * return value of @val. If @error is nonzero, it's a negated errno
    + * code; the user sees a failed system call with this errno code.
    + *
    + * It's only valid to call this when @task is stopped for tracing on exit
    + * from a system call, due to %TIF_SYSCALL_TRACE or %TIF_SYSCALL_AUDIT.
    + */
    +void syscall_set_return_value(struct task_struct *task, struct pt_regs *regs,
    + int error, long val);
    +
    +/**
    + * syscall_get_arguments - extract system call parameter values
    + * @task: task of interest, must be blocked
    + * @regs: task_pt_regs() of @task
    + * @i: argument index [0,5]
    + * @n: number of arguments; n+i must be [1,6].
    + * @args: array filled with argument values
    + *
    + * Fetches @n arguments to the system call starting with the @i'th argument
    + * (from 0 through 5). Argument @i is stored in @args[0], and so on.
    + * An arch inline version is probably optimal when @i and @n are constants.
    + *
    + * It's only valid to call this when @task is stopped for tracing on
    + * entry to a system call, due to %TIF_SYSCALL_TRACE or %TIF_SYSCALL_AUDIT.
    + * It's invalid to call this with @i + @n > 6; we only support system calls
    + * taking up to 6 arguments.
    + */
    +void syscall_get_arguments(struct task_struct *task, struct pt_regs *regs,
    + unsigned int i, unsigned int n, unsigned long *args);
    +
    +/**
    + * syscall_set_arguments - change system call parameter value
    + * @task: task of interest, must be in system call entry tracing
    + * @regs: task_pt_regs() of @task
    + * @i: argument index [0,5]
    + * @n: number of arguments; n+i must be [1,6].
    + * @args: array of argument values to store
    + *
    + * Changes @n arguments to the system call starting with the @i'th argument.
    + * @n'th argument to @val. Argument @i gets value @args[0], and so on.
    + * An arch inline version is probably optimal when @i and @n are constants.
    + *
    + * It's only valid to call this when @task is stopped for tracing on
    + * entry to a system call, due to %TIF_SYSCALL_TRACE or %TIF_SYSCALL_AUDIT.
    + * It's invalid to call this with @i + @n > 6; we only support system calls
    + * taking up to 6 arguments.
    + */
    +void syscall_set_arguments(struct task_struct *task, struct pt_regs *regs,
    + unsigned int i, unsigned int n,
    + const unsigned long *args);
    +
    +#endif /* _ASM_SYSCALL_H */
    diff --git a/include/linux/tracehook.h b/include/linux/tracehook.h
    index 32867ab..589f429 100644
    --- a/include/linux/tracehook.h
    +++ b/include/linux/tracehook.h
    @@ -103,7 +103,8 @@ static inline void ptrace_report_syscall(struct pt_regs *regs)
    * the system call. That must prevent normal entry so no system call is
    * made. If @task ever returns to user mode after this, its register state
    * is unspecified, but should be something harmless like an %ENOSYS error
    - * return.
    + * return. It should preserve enough information so that syscall_rollback()
    + * can work (see asm-generic/syscall.h).
    *
    * Called without locks, just after entering kernel mode.
    */

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