Messages in this thread | | | Date | Mon, 17 Dec 2007 16:52:40 -0500 | From | Masami Hiramatsu <> | Subject | Re: FInal kprobes rollup patches |
| |
Hi Harvey,
Harvey Harrison wrote: > On Mon, 2007-12-17 at 16:28 -0500, Masami Hiramatsu wrote: >> Hi Harvey, >> If you mention about a relative jump which is inserted by >> resume_execution(), I think you might misunderstand that relative jump. >> >> The size of that relative jump, which will be embedded by kprobe-booster, is >> 5-bytes(not 1 byte). So it needs 5 bytes space. >> And we decided not to expand MAX_INSN_SIZE when we developed the booster. >> The reasons are: >> - it is supplemental feature(just accelerating kprobes), if we have no space, >> we can disable it. >> - 5 bytes are big enough compared with 15(=MAX_INSN_SIZE) >> - the lengths of most of instructions are less than 10 bytes. >> >> Additionally, MAX_INSN_SIZE is used in kernel/kprobes.c to allocate an >> instruction buffer which will be assigned to p->ainsn.insn. Since the >> instruction buffer size is MAX_INSN_SIZE, you can not copy instructions >> more than MAX_INSN_SIZE. >> >> BTW, in my patch, I unified MAX_INSN_SIZE to bigger one(16). >> I think it is enough for us. >> > > I went with 15 in mine, I thought it made the code a little more > readable, but I will defer if you think 16 is better. If you want me > to send the whole series to you, let me know.
Before porting, could you tell me what differences are important to you? We can discuss about it.
> I just sent out a series of 4 patches equivalent to your patches 1-4/6 > but based on my already unified kprobes.c/h, You may want to check your > handling of restored registers in trampoline_probe_handler which I found > when rebasing yours on top of my cleanups. Not sure if this is > important, but it was a difference I found. > > X86_32: > regs->cs = __KERNEL_CS | get_kernel_rpl(); > > yours: > regs->cs = __KERNEL_CS;
Because of kretprobe's compatibility, on x86-32 cs should be set rpl(). But get_kernel_rpl() does not exist on x86-64.
Thanks,
-- Masami Hiramatsu
Software Engineer Hitachi Computer Products (America) Inc. Software Solutions Division
e-mail: mhiramat@redhat.com, masami.hiramatsu.pt@hitachi.com
| |