Re: Bug in setbpt/clearbpt for SPARC/SPARC64?

[Dmitry V. L. <ld...@al...>]

Hi,

On Wed, Nov 28, 2012 at 01:14:33PM +0000, James Hogan wrote:
> 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?

Yes, there seems to be a bug on SPARC/SPARC64 where change_syscall is
effectively disabled due to the way how it is implemented.


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ldv