Hi Harvey, Harvey Harrison wrote: > On Mon, 2007-12-17 at 19:52 +0530, Srikar Dronamraju wrote: >> * Ingo Molnar <[EMAIL PROTECTED]> [2007-12-15 14:12:04]: >> >> >> Hi Ingo, Harvey >> >> In file include/asm-x86/kprobes_32.h >> typedef u8 kprobe_opcode_t; >> hence sizeof(kprobe_opcode_t) turns out to be 1. >> >> Hence >> >> memcpy(p->ainsn.insn, p->addr, MAX_INSN_SIZE * sizeof(kprobe_opcode_t)); >> is correct. >> > > OK, but this would be much clearer to adopt the X86_64 way, define > MAX_INSN_SIZE one smaller and make this line: > > /* Copy original instruction plus space for 1 byte relative jump */ > memcpy(p->ainsn.insn, p->addr, MAX_INSN_SIZE + sizeof(kprobe_opcode_t)); > > See the first patch of my cleanup work that unified MAX_INSN_SIZE > and you'll see why this jumped out. > > 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. Thanks, Best Regards, -- Masami Hiramatsu Software Engineer Hitachi Computer Products (America) Inc. Software Solutions Division e-mail: [EMAIL PROTECTED], [EMAIL PROTECTED] -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/