Bug in setbpt/clearbpt for SPARC/SPARC64?

[James Hogan]

Hi

While implementing regset support in strace for the metag architecture,
I think I've noticed a problem in util.c.

For SPARC/SPARC64, arg_setup and arg_finish_change are defined to use
PTRACE_GETREGS and PTRACE_SETREGS. However change_syscall also does a
read-modify-write using PTRACE_GETREGS and PTRACE_SETREGS.

These are then combined in a bad way in setbpt:

if (arg_setup(tcp, &state) < 0
/* reads the registers into state */
    || get_arg0(tcp, &state, &tcp->inst[0]) < 0
    || get_arg1(tcp, &state, &tcp->inst[1]) < 0
/* reads arguments from state */
    || change_syscall(tcp, clone_scno[current_personality]) < 0
/* reads registers again, and changes one of them */
    || set_arg0(tcp, &state, CLONE_PTRACE|SIGCHLD) < 0
    || set_arg1(tcp, &state, 0) < 0
/* sets argument registers in state */
    || arg_finish_change(tcp, &state) < 0)
/* writes back state, presumably undoing change_syscall's hard work. */

Looking at a "git diff v4.7..master util.c", it looks like clearbpt is
doing something similar too.

Is that analysis correct or have I missed something important that would
make it work?

Thanks
James