Hi Gabriel, I follow your suggestion and use ChangeDoChildrenPost and also
not mutate things directly. I also use method vstmt instead of method
vinstr. Below is my new version for changing
sprintf(buff,"a string")
to
snprintf(buff,sizeof(buff","a string").
Please let me know if there's any possible side-effects in there.
Another question is that the code I have change the statement of the form
sprintf(buff,"a string") to snprintf(...) , so if I want to change a
different statement of the form something=sprintf(buff,"a string") to
something=snprintf, or foo(sprintf()) to foo(snprintf) ... , then I
would need to rewrite another pattern matching , e.g., match ins with Set
instead of Call ? Is there a more general way to not having to do a pattern
matching for every case ?
Thanks
let snprintf_va = makeVarinfo true "snprintf" (TVoid [])
let snprintf = Lval((Var snprintf_va),NoOffset)
class snprintfV ?(tracelist=[]) file = object
inherit nopCilVisitor
method vstmt s = ChangeDoChildrenPost(
s,
fun s -> if L.mem (s.sid) tracelist then (
match s.skind with
|Instr il -> let new_il = L.map (
fun ins -> match ins with
|Call(None,Lval(Var {vname="sprintf"},_),expl,loc)->
let to_buf = L.hd expl in
Call(None,snprintf,to_buf::(SizeOfE(to_buf)::L.tl
expl),loc)
| _ -> ins
) il in
debug "old stmt:\n%s\nnew stmt:\n%s\n" (get_stmt s) (get_stmt
(mkStmt(Instr new_il)));
{s with skind = Instr new_il}
| _ -> s
)else s
)
end
VN -
2009/12/17 Gabriel Kerneis <[email protected]>
> Hi,
>
> On Thu, Dec 17, 2009 at 03:46:32PM -0700, ThanhVu (Vu) Nguyen wrote:
> > 1) After I change the original statement s to a new one s' , I want
> > s'.id to be the same as s.id. Using the "method vinst", I
> cannot do
> > this.
>
> You can, but you have to use the mutable property of the fields rather
> than returning ChangeTo (which will build a new statement, i.e. generate
> a new id). In that case, you seem to be stuck with hacking things in
> vstmt as you originally did (but I might have overlooked some clever way
> to proceed).
>
> I juste realized that the following could work (to be tested):
>
> method vstmt s = match s.skind with
> | Instr l ->
> ChangeDoChildrenPost (s, fun new_s ->
> new_s.sid <- s.sid; new_s)
> | _ -> DoChildren
>
> This should restore the sid (no idea if anything bad can happen).
>
>
> > 2) Does it look correct ?
>
> No.
>
> > method vinst i = (
> > match i with
> > |Call (None,Lval(Var v,os),expl,loc) -> (
> > v.vname <- v.vname ^ "_NEW" ;
>
> This is an example of mutating things directly, but you have to remember
> that the varinfo is *shared* across your program (i.e. a given single
> varinfo is used everywhere you need to invoke some variable).
> Hence, here, you are adding _NEW not only in some precise spots, but
> everywhere in your program as a side-effect.
>
> You should build a copy of the variable with a different vname, and use
> this one instead:
> let v' = { v with vname = v.vname ^ "_NEW" } in
> ChangeTo([ ... v' ... ])
>
> This might break some CIL invariant, though, since the v' variable is
> not declared in the AST.
>
> > ChangeTo([Call(None,Lval(Var v,os),expl,loc)])
> > )
> > |_ -> SkipChildren
> > )
>
>
> > What I intend to do eventually is changing statements "sprintf" to
> > "snprintf". Note that I don't want to change _all_ of these sprintf
> > statements but only specific ones based on their sid's.
>
> The clean solution in your case is to use Cil.findOrCreateFunc to
> initialize some varinfo (with snprintf) and use it directly in vinst:
>
> class sprintfV file =
> let snprintf_typ = (* you have to figure it out manually... *) in
> let snprintf_vi = findOrCreateFunc file "snprintf" snprintf_typ in
> object
> ...
> method vinst i =
> ...
> use snprintf_vi here instead of v'
> ...
> ...
> end
>
> Regards,
> --
> Gabriel Kerneis
>
>
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