Re: [RFC] Proposal for ptrace improvements

[Linus Torvalds]

On Fri, Mar 4, 2011 at 9:05 AM, Denys Vlasenko <vda.linux@xxxxxxxxxxxxxx> wrote:
>
> Here's a typical sequence of operations strace is doing:
>
> wait4(-1, [{WIFSTOPPED(s) && WSTOPSIG(s) == SIGTRAP}], __WALL, NULL) = 10445
> ptrace(PTRACE_GETSIGINFO, 10445, 0, {si_signo=SIGTRAP, si_code=0x5,
> si_pid=10445, si_uid=0, si_value={int=0, ptr=0}}) = 0
> ptrace(PTRACE_PEEKUSER, 10445, 8*ORIG_RAX, [0x36]) = 0
> ptrace(PTRACE_PEEKUSER, 10445, 8*CS, [0x23]) = 0
> ptrace(PTRACE_PEEKUSER, 10445, 8*RAX, [0xffffffffffffffda]) = 0
> ptrace(PTRACE_PEEKUSER, 10445, 8*RBX, [0x1]) = 0
> ptrace(PTRACE_PEEKUSER, 10445, 8*RCX, [0x5401]) = 0
> ptrace(PTRACE_PEEKUSER, 10445, 8*RDX, [0xffb83f10]) = 0
> ptrace(PTRACE_SYSCALL, 10445, 0x1, SIG_0) = 0
>
> IOW: strace wastes a lot of time just transiting to the kernel and back
> with simple syscalls to get the information.
>
> What would help here is a "vectorized" waitpid operation
> which retrieves much more information in one go:
>
> waitpid_vec(int max_results, int status_vector[], siginfo_t
> si_vector[], struct pt_regs reg_vector[])

No. Start off with what we already have: make ptrace use
"PTRACE_GETREGSET" instead of PTRACE_PEEKUSER.

That should get the whole "user_regs_struct" in one single system call.

                                      Linus
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