[PATCH v2] cmd: setexpr: fix no matching string in gsub return empty value

[Massimiliano Minella]

Hello,

On Tue, Oct 8, 2024 at 7:20 PM Francesco Dolcini <francesco at dolcini.it> wrote:
>
> +Tom
>
> Hello Massimiliano,
>
> On Tue, Sep 03, 2024 at 01:06:21PM +0200, Michal Simek wrote:
> > HI,
> >
> > čt 8. 2. 2024 v 16:00 odesílatel Massimiliano Minella
> > <massimiliano.minella at gmail.com> napsal:
> > >
> > > From: Massimiliano Minella <massimiliano.minella at se.com>
> > >
> > > In gsub, when the destination string is empty, the string 't' is
> > > provided and the regular expression doesn't match, then the final result
> > > is an empty string.
> > >
> > > Example:
> > >
> > > => echo ${foo}
> > >
> > > => setenv foo
> > > => setexpr foo gsub e a bar
> > > => echo ${foo}
> > >
> > > =>
> > >
> > > The variable ${foo} should contain "bar" and the lack of match shouldn't
> > > be considered an error.
> > >
> > > This patch fixes the erroneous behavior by removing the return
> > > statement and breaking out of the loop in case of lack of match.
> > >
> > > Also add a test for the no match case.
> > >
> > > Signed-off-by: Massimiliano Minella <massimiliano.minella at se.com>
> > > ---
> > > Changes in V2:
> > >  - update documentation to describe the behavior
> > >
> > >  cmd/setexpr.c             |  9 ++++-----
> > >  doc/usage/cmd/setexpr.rst |  1 +
> > >  test/cmd/setexpr.c        | 10 ++++++++++
> > >  3 files changed, 15 insertions(+), 5 deletions(-)
> > >
> > > diff --git a/cmd/setexpr.c b/cmd/setexpr.c
> > > index 233471f6cb..ab76824a32 100644
> > > --- a/cmd/setexpr.c
> > > +++ b/cmd/setexpr.c
> > > @@ -216,14 +216,12 @@ int setexpr_regex_sub(char *data, uint data_size, char *nbuf, uint nbuf_size,
> > >                 if (res == 0) {
> > >                         if (loop == 0) {
> > >                                 debug("%s: No match\n", data);
> > > -                               return 1;
> >
> > This patch actually changed the return value from command.
> > In board/xilinx/zynqmp/zynqmp_kria.env we have
> >
> > bootcmd=setenv model $board_name && if setexpr model gsub
> > .*$k24_starter* $k24_starter || setexpr model gsub .*$k26_starter*
> > $k26_starter; then run som_cc_boot; else run som_mmc_boot; run
> > som_cc_boot; fi
> >
> > and this patch actually breaked it because we rely on return value.
> > Changing return value is not described and I want to know if this
> > patch should be fixed
> > or we should update our commands to match new return value.
>
> Massimilano, any comment on this?
>
> This change broke also our use case - our board is no longer booting
> with v2024.10 U-Boot. I do not think we should change something like
> that without a clear reason and I was not able to understand it from the
> commit message.

The reason why I proposed the patch was that I found the behavior of setexpr
gsub not consistent with the behavior of the same function in gawk, which,
according to the commit message that introduced gsub/sub, both commands are
closely modeled after. Also I didn't see a particular reason for returning an
empty string or throwing an error when doing a string substitution that provides
no match, so IMHO it was a bug.

>From a quick grep on the master branch it seems that the command is used only in
board/xilinx/zynqmp/zynqmp_kria.env and include/env/ti/ti_common.env. In the
first I see it has already been fixed and in the second the change has no
impact.

It's unfortunate that it broke the boot of your board, maybe something as it has
been done for the zynqmp_kria is feasible according to your use of the command?

Regards,
Massimiliano