xtrace output sets ERRNO to 9 (EBADF)

xtrace output sets ERRNO to 9 (EBADF)

[Stephane Chazelas]

$ ./Src/zsh -c 'set -o xtrace; ERRNO=0; :; echo "$ERRNO"'
+zsh:1> ERRNO=0
+zsh:1> :
+zsh:1> echo 9
9

Seems to be caused by a double-close. From strace:

dup(2)                                  = 3
fcntl(3, F_DUPFD, 10)                   = 12
close(3)                                = 0
fcntl(12, F_GETFL)                      = 0x1 (flags O_WRONLY)
newfstatat(12, "", {st_mode=S_IFIFO|0600, st_size=0, ...}, AT_EMPTY_PATH) = 0
brk(0x557861189000)                     = 0x557861189000
write(12, "+zsh:1> :\n", 10+zsh:1> :
)            = 10
close(12)                               = 0
brk(0x557861188000)                     = 0x557861188000
close(12)                               = -1 EBADF (Bad file descriptor)

(on Debian GNU/Linux amd64 with 5.9 or git HEAD).

-- 
Stephane

Re: xtrace output sets ERRNO to 9 (EBADF)

[Bart Schaefer]

diff --git a/Src/exec.c b/Src/exec.c
index 1810fca5e..a1059af5e 100644
--- a/Src/exec.c
+++ b/Src/exec.c
@@ -4336,10 +4336,13 @@ execcmd_exec(Estate state, Execcmd_params eparams,
     }
     }
     if (newxtrerr) {
+    int eno = errno;
     fil = fileno(newxtrerr);
     fclose(newxtrerr);
     xtrerr = oxtrerr;
+    /* Call zclose() to clean up internal tables, ignore EBADF */
     zclose(fil);
+    errno = eno;
     }

     zsfree(STTYval);

Re: xtrace output sets ERRNO to 9 (EBADF)

[Daniel Shahaf]

Bart Schaefer wrote on Fri, Dec 09, 2022 at 18:57:37 -0800:
> diff --git a/Src/exec.c b/Src/exec.c
> index 1810fca5e..a1059af5e 100644
> --- a/Src/exec.c
> +++ b/Src/exec.c
> @@ -4336,10 +4336,13 @@ execcmd_exec(Estate state, Execcmd_params eparams,
>      }
>      }
>      if (newxtrerr) {
> +    int eno = errno;
>      fil = fileno(newxtrerr);
>      fclose(newxtrerr);
>      xtrerr = oxtrerr;
> +    /* Call zclose() to clean up internal tables, ignore EBADF */
>      zclose(fil);
> +    errno = eno;

This ignores any errors from the fileno() and fclose() calls as well, though?

>      }
> 
>      zsfree(STTYval);
> 

Re: xtrace output sets ERRNO to 9 (EBADF)

[Stephane Chazelas]

2022-12-10 11:38:13 +0000, Daniel Shahaf:
> Bart Schaefer wrote on Fri, Dec 09, 2022 at 18:57:37 -0800:
> > diff --git a/Src/exec.c b/Src/exec.c
> > index 1810fca5e..a1059af5e 100644
> > --- a/Src/exec.c
> > +++ b/Src/exec.c
> > @@ -4336,10 +4336,13 @@ execcmd_exec(Estate state, Execcmd_params eparams,
> >      }
> >      }
> >      if (newxtrerr) {
> > +    int eno = errno;
> >      fil = fileno(newxtrerr);
> >      fclose(newxtrerr);
> >      xtrerr = oxtrerr;
> > +    /* Call zclose() to clean up internal tables, ignore EBADF */
> >      zclose(fil);
> > +    errno = eno;
> 
> This ignores any errors from the fileno() and fclose() calls as well, though?
[...]

Yes, though it's probably just  as well. Users use $ERRNO to
detect errors while doing operations they asked for.

In my case, I was doing:

ERRNO=0
files=(**/someglob(N))
if (( ERRNO )) ...

To check for errors during the glob expansion (wanting to make
sure that it doesn't missing anythin).

And finding that that glob expansion seemingly failed with EBADF
when run under zsh -x.

-- 
Stephane

Re: xtrace output sets ERRNO to 9 (EBADF)

[Bart Schaefer]

On Sun, Dec 11, 2022 at 10:36 AM Stephane Chazelas
<stephane@chazelas.org> wrote:
>
> > This ignores any errors from the fileno() and fclose() calls as well, though?
>
> Yes, though it's probably just  as well. Users use $ERRNO to
> detect errors while doing operations they asked for.

Exactly; xtrace shouldn't be affecting program errors.  In any case,
fileno() doesn't set errno (it's just a data structure deref, would
only fail by crashing) and zclose() already clobbers the error from
fclose().

Re: xtrace output sets ERRNO to 9 (EBADF)

[Stephane Chazelas]

2022-12-11 10:52:44 -0800, Bart Schaefer:
[...]
> In any case,
> fileno() doesn't set errno (it's just a data structure deref, would
> only fail by crashing)

Not that it matters much here, but POSIX does say that fileno()
shall  return -1 EBADF if "The stream is not associated with a
file." and may if "The file descriptor underlying stream is not
a valid file descriptor."

https://pubs.opengroup.org/onlinepubs/9699919799.2018edition/functions/fileno.html

musl libc has:

int fileno(FILE *f)
{
        FLOCK(f);
        int fd = f->fd;
        FUNLOCK(f);
        if (fd < 0) {
                errno = EBADF;
                return -1;
        }
        return fd;
}

-- 
Stephane