Re: Changing $0 after gsub() breaks output

[arnold]

Thanks. Fixed. Pushed to git.

Arnold

Yasuhiro Yamada <yamada@gr3.ie> wrote:

> Thanks for identifying and fixing the problem.
>
> > +                        * (Test case was gawk 'gusb(/./, "@") && $0=$1'). 
> > So we save
>
> I noticed a minor typo by the way.
> s/gusb/gsub/
>
> Thanks,
>
> On Sun, Jan 29, 2023 at 7:53 AM <arnold@skeeve.com> wrote:
> >
> > Hi.
> >
> > Thank you for the bug report and easy reproducer. The patch
> > below fixes the problem. It will be in Git in the next
> > day or two.
> >
> > Arnold
> >
> > Yasuhiro Yamada <yamada@gr3.ie> wrote:
> >
> > > Hi.
> > > Executing gsub() without an action and making changes to $0 will
> > > corrupt the output.
> > > This behavior seems like a bug.
> > >
> > >     $ ./gawk --version
> > >     GNU Awk 5.2.1, API 3.2, PMA Avon 8-g1
> > >     ...
> > >     $ echo abc | ./gawk 'gsub(".","@") && $0=$1'
> > >     q  <===== broken output
> > >
> > > Interestingly, the result is different for each run.
> > >
> > >     $ echo abc | ./gawk 'gsub(".","@") && $0=$1' | od -tx1c
> > >     0000000  b0  61  99  0a
> > >              260   a 231  \n
> > >     0000004
> > >     $ echo abc | ./gawk 'gsub(".","@") && $0=$1' | od -tx1c
> > >     0000000  c0  e7  f7  0a
> > >             300 347 367  \n
> > >     0000004
> > >     $ echo abc | ./gawk 'gsub(".","@") && $0=$1' | od -tx1c
> > >     0000000  c0  07  14  0a
> > >             300  \a 024  \n
> > >     0000004
> > >     $ echo abc | ./gawk 'gsub(".","@") && $0=$1' | od -tx1c
> > >     0000000  c0  57  76  0a
> > >             300   W   v  \n
> > >     0000004
> > >
> > > Older versions do NOT reproduce this issue.
> > > Also, the outputs are as expected and intuitive.
> > >
> > >     $ ./gawk --version
> > >     GNU Awk 4.1.4, API: 1.1
> > >     ...
> > >     $ echo abc | ./gawk 'gsub(".","@") && $0=$1'
> > >     @@@
> > >     $ echo abc | ./gawk 'gsub(".","@") && $0=$1' | od -tx1c
> > >     0000000  40  40  40  0a
> > >               @   @   @  \n
> > >     0000004
> > >
> > > This issue seems to occur in v4.2.0 and later.
> > >
> > >     $ ./gawk --version
> > >     GNU Awk 4.2.0, API: 2.0
> > >     ...
> > >     $ echo abc | ./gawk 'gsub(".","@") && $0=$1' | od -tx1c
> > >     0000000  e0  4f  fc  0a
> > >             340   O 374  \n
> > >     0000004
> > >
> > > My environment is
> > >
> > >     $ uname -a
> > >     Linux ip-172-31-9-222 5.4.0-1093-aws #102~18.04.2-Ubuntu SMP Wed
> > > Dec 7 00:31:59 UTC 2022 x86_64 x86_64 x86_64 GNU/Linux
> > >     $ gcc --version
> > >     gcc (Ubuntu 7.5.0-3ubuntu1~18.04) 7.5.0
> >
> > ---------------------------------------------
> > diff --git a/interpret.h b/interpret.h
> > index 4540d302..5adb229b 100644
> > --- a/interpret.h
> > +++ b/interpret.h
> > @@ -872,16 +874,30 @@ mod:
> >                         break;
> >
> >                 case Op_assign:
> > +               {
> > +                       NODE *save_lhs;
> > +
> >                         lhs = POP_ADDRESS();
> >                         r = TOP_SCALAR();
> > -                       unref(*lhs);
> > +                       /*
> > +                        * 1/2023:
> > +                        * The old NODE pointed to by *lhs has to be freed.
> > +                        * But we can't free it too early, in case it's 
> > both $0 and $1
> > +                        * (Test case was gawk 'gusb(/./, "@") && $0=$1'). 
> > So we save
> > +                        * the old one, and after the assignment, we free 
> > it, since
> > +                        * $0 and $1 have the same stptr value but only $0 
> > has MALLOC
> > +                        * in the flags. Whew!
> > +                        */
> > +                       save_lhs = *lhs;
> >                         if (r->type == Node_elem_new) {
> >                                 DEREF(r);
> >                                 r = dupnode(Nnull_string);
> >                         }
> >                         UPREF(r);
> >                         UNFIELD(*lhs, r);
> > +                       unref(save_lhs);
> >                         REPLACE(r);
> > +               }
> >                         break;
> >
> >                 case Op_subscript_assign: