Re: [PATCH v3] trace2: refactor to avoid gcc warning under -O3

[Jeff King <peff@peff.net>]

On Fri, May 21, 2021 at 07:08:11AM +0900, Junio C Hamano wrote:

> Jeff King <peff@peff.net> writes:
> 
> >> @@ -287,7 +285,7 @@ static int tr2_dst_try_unix_domain_socket(struct tr2_dst *dst,
> >>  	if (tr2_dst_want_warning())
> >>  		warning("trace2: could not connect to socket '%s' for '%s' tracing: %s",
> >>  			path, tr2_sysenv_display_name(dst->sysenv_var),
> >> -			strerror(e));
> >> +			strerror(errno));
> >
> > We expect the value of errno to persist across tr2_dst_want_warning()
> > and tr2_sysenv_display_name() here. The former may call getenv() and
> > atoi(). I think that's probably fine, but if we wanted to be really
> > paranoid, we'd have to preserve errno manually here, too.
> 
> Being "really paranoid" consistently within the file would mean a
> change like the attached, I would think, on top of what was posted.
> 
> Or tr2_dst_want_warning() and tr2_sysenv_display_name() can be
> taught to preserve errno like tr2_dst_dry_uds_connect() was taught
> to do so by the patch under discussion, which may reduce the amount
> of apparent change, but constantly moving the contents of errno
> around just in case we later might want to use its value feels
> dirty.
> 
> I dunno.
> 
>  trace2/tr2_dst.c | 14 +++++++++++---
>  1 file changed, 11 insertions(+), 3 deletions(-)

Ah, yeah. I didn't look to see if there were existing cases of the same
thing.

I could go either way on this kind of saved_errno thing in general (the
tr2 functions called in between are really quite unlikely to set errno
(I am not even sure if getenv() and atoi() can, so this really might
just be future-proofing in case those tr2 functions get more
complicated).

But seeing that there are other cases of the same, I definitely think it
is not something that should be in Ævar's patch. It is a cleanup we
could do on top if we cared to.

-Peff