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SubjectRe: [RFC PATCH v2 4/6] uprobes/x86: Emulate rip-relative call's
On 04/09/2014 09:44 PM, Oleg Nesterov wrote:
> +static void ttt_clear_displacement(struct arch_uprobe *auprobe, struct insn *insn)

Branch instruction's offset isn't called "displacement"
on x86.

How about ttt_clear_branch_offset?

> +{
> + /*
> + * Turn this insn into "call 1f; 1:", this is what we will execute
> + * out-of-line if ->emulate() fails.
> + *
> + * In the likely case this will lead to arch_uprobe_abort_xol(), but
> + * see the comment in ->emulate(). So we need to ensure that the new
> + * ->ip can't fall into non-canonical area and trigger #GP.
> + *
> + * We could turn it into (say) "pushf", but then we would need to
> + * divorce ->insn[] and ->ixol[]. We need to preserve the 1st byte
> + * of ->insn[] for set_orig_insn().
> + */
> + memset(auprobe->insn + insn_offset_immediate(insn),
> + 0, insn->immediate.nbytes);
> +}



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