• Andrey Vagin's avatar
    ptrace: add ability to retrieve signals without removing from a queue (v4) · 84c751bd
    Andrey Vagin authored
    This patch adds a new ptrace request PTRACE_PEEKSIGINFO.
    This request is used to retrieve information about pending signals
    starting with the specified sequence number.  Siginfo_t structures are
    copied from the child into the buffer starting at "data".
    The argument "addr" is a pointer to struct ptrace_peeksiginfo_args.
    struct ptrace_peeksiginfo_args {
    	u64 off;	/* from which siginfo to start */
    	u32 flags;
    	s32 nr;		/* how may siginfos to take */
    "nr" has type "s32", because ptrace() returns "long", which has 32 bits on
    i386 and a negative values is used for errors.
    Currently here is only one flag PTRACE_PEEKSIGINFO_SHARED for dumping
    signals from process-wide queue.  If this flag is not set, signals are
    read from a per-thread queue.
    The request PTRACE_PEEKSIGINFO returns a number of dumped signals.  If a
    signal with the specified sequence number doesn't exist, ptrace returns
    zero.  The request returns an error, if no signal has been dumped.
    EINVAL - one or more specified flags are not supported or nr is negative
    EFAULT - buf or addr is outside your accessible address space.
    A result siginfo contains a kernel part of si_code which usually striped,
    but it's required for queuing the same siginfo back during restore of
    pending signals.
    This functionality is required for checkpointing pending signals.  Pedro
    Alves suggested using it in "gdb" to peek at pending signals.  gdb already
    uses PTRACE_GETSIGINFO to get the siginfo for the signal which was already
    dequeued.  This functionality allows gdb to look at the pending signals
    which were not reported yet.
    The prototype of this code was developed by Oleg Nesterov.
    Signed-off-by: default avatarAndrew Vagin <avagin@openvz.org>
    Cc: Roland McGrath <roland@redhat.com>
    Cc: Oleg Nesterov <oleg@redhat.com>
    Cc: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
    Cc: David Howells <dhowells@redhat.com>
    Cc: Dave Jones <davej@redhat.com>
    Cc: "Michael Kerrisk (man-pages)" <mtk.manpages@gmail.com>
    Cc: Pavel Emelyanov <xemul@parallels.com>
    Cc: Linus Torvalds <torvalds@linux-foundation.org>
    Cc: Pedro Alves <palves@redhat.com>
    Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
    Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
ptrace.c 29.4 KB