• David S. Miller's avatar
    sparc: Fix debugger syscall restart interactions. · 28e61036
    David S. Miller authored
    So, forever, we've had this ptrace_signal_deliver implementation
    which tries to handle all of the nasties that can occur when the
    debugger looks at a process about to take a signal.  It's meant
    to address all of these issues inside of the kernel so that the
    debugger need not be mindful of such things.
    
    Problem is, this doesn't work.
    
    The idea was that we should do the syscall restart business first, so
    that the debugger captures that state.  Otherwise, if the debugger for
    example saves the child's state, makes the child execute something
    else, then restores the saved state, we won't handle the syscall
    restart properly because we lose the "we're in a syscall" state.
    
    The code here worked for most cases, but if the debugger actually
    passes the signal through to the child unaltered, it's possible that
    we would do a syscall restart when we shouldn't have.
    
    In particular this breaks the case of debugging a process under a gdb
    which is being debugged by yet another gdb.  gdb uses sigsuspend
    to wait for SIGCHLD of the inferior, but if gdb itself is being
    debugged by a top-level gdb we get a ptrace_stop().  The top-level gdb
    does a PTRACE_CONT with SIGCHLD to let the inferior gdb see the
    signal.  But ptrace_signal_deliver() assumed the debugger would cancel
    out the signal and therefore did a syscall restart, because the return
    error was ERESTARTNOHAND.
    
    Fix this by simply making ptrace_signal_deliver() a nop, and providing
    a way for the debugger to control system call restarting properly:
    
    1) Report a "in syscall" software bit in regs->{tstate,psr}.
       It is set early on in trap entry to a system call and is fully
       visible to the debugger via ptrace() and regsets.
    
    2) Test this bit right before doing a syscall restart.  We have
       to do a final recheck right after get_signal_to_deliver() in
       case the debugger cleared the bit during ptrace_stop().
    
    3) Clear the bit in trap return so we don't accidently try to set
       that bit in the real register.
    
    As a result we also get a ptrace_{is,clear}_syscall() for sparc32 just
    like sparc64 has.
    
    M68K has this same exact bug, and is now the only other user of the
    ptrace_signal_deliver hook.  It needs to be fixed in the same exact
    way as sparc.
    Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
    28e61036
signal.c 18.1 KB