On 04/28, Denys Vlasenko wrote:
>
> It is possible to replace rip-relative addressing mode
> with addressing mode of the same length: (reg+disp32).
> This eliminates the need to fix up immediate
> and instruction length.
"and change instruction length", I presume.
I like this patch very much, and I would be happy to ack everything
except this part:
> @@ -307,22 +313,13 @@ static void riprel_analyze(struct arch_uprobe *auprobe,
> struct insn *insn)
> * #1) for the scratch register.
> */
> auprobe->def.fixups |= UPROBE_FIX_RIP_CX;
> - /* Change modrm from 00 000 101 to 00 000 001. */
> - *cursor = 0x1;
> + /* Change modrm from 00 000 101 to 10 000 001. */
> + *cursor = 0x81;
> } else {
> /* Use %rax (register #0) for the scratch register. */
> auprobe->def.fixups |= UPROBE_FIX_RIP_AX;
> - /* Change modrm from 00 xxx 101 to 00 xxx 000 */
> - *cursor = (reg << 3);
> - }
> -
> - /* Target address = address of next instruction + (signed) offset */
> - auprobe->def.riprel_target = (long)insn->length +
> insn->displacement.value;
> -
> - /* Displacement field is gone; slide immediate field (if any) over. */
> - if (insn->immediate.nbytes) {
> - cursor++;
> - memmove(cursor, cursor + insn->displacement.nbytes,
> insn->immediate.nbytes);
> + /* Change modrm from 00 xxx 101 to 10 xxx 000 */
> + *cursor = (reg << 3) | 0x80;
> }
As you know, this is black magic for me.
Masami, Jim, please review and ack/nack?
> @@ -343,26 +340,17 @@ static void riprel_pre_xol(struct arch_uprobe *auprobe,
> struct pt_regs *regs)
> unsigned long *sr = scratch_reg(auprobe, regs);
>
> utask->autask.saved_scratch_register = *sr;
> - *sr = utask->vaddr + auprobe->def.riprel_target;
> + *sr = utask->vaddr + (int)auprobe->def.ilen;
^^^^^
Why? This is pointless and even misleading. I'll remove this part if you
do not object.
Oleg.
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