Messages in this thread | | | From | Denys Vlasenko <> | Subject | Re: [RFC] Proposal for ptrace improvements | Date | Fri, 4 Mar 2011 19:59:57 +0100 |
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On Friday 04 March 2011 18:12, Linus Torvalds wrote: > On Fri, Mar 4, 2011 at 9:05 AM, Denys Vlasenko <vda.linux@googlemail.com> 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.
Aye. That's the idea: get more info in one go.
I bet a part of the rationale for PTRACE_GETREGSET was to get not one register per syscall, but all of them.
We have more of these:
readv/writev
Get not one signal, but many of them (signalfd).
Get not one task's wait notification, but many of them, and also get accompanying siginfo etc (waitpidv? or better, waitfd?)
-- vda
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