Messages in this thread | | | Subject | Re: [RFC PATCH 0/6] uprobes/x86: fix the reprel jmp/call handling | From | Jim Keniston <> | Date | Mon, 07 Apr 2014 11:54:12 -0700 |
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On Sun, 2014-04-06 at 22:15 +0200, Oleg Nesterov wrote: > On 04/04, Jim Keniston wrote: > > > > On Fri, 2014-04-04 at 21:32 +0200, Oleg Nesterov wrote: > > > > > > 1. Why insn_get_displacement() doesn't work? See "HELP!!!" > > > below. > > > > insn->moffset1.value seems to be what you want. > > Works! Thanks a lot. > > Still I can't understand why displacement.nbytes == 0 in this case... > Nevermind.
Looking at Masami's arch/x86/lib/x86-opcode-map.txt and related code, I see that the operands to the Jcc and JMP instructions are treated as immediate values. So insn->immediate.value (which is in the same union as insn->moffset1.value) is more appropriate, and insn->immediate.nbytes should get you the correct size. Again, insn_get_length() finishes parsing the whole instruction as necessary, so insn_get_immediate() gets called as a side effect.
> > OK. Please see the RFC changes. Obviously not for inclusion yet. And > totally untested, except I verified that the test-case from 4/6 works. > > Please comment.
I'll look at the new patches today.
> > Oleg.
Jim
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