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

Hi Junio,

On Fri, 7 May 2021, Junio C Hamano wrote:

Johannes Schindelin [off-list ref] writes:

quoted

quoted

Otherwise I'd strongly prefer to see a word that hints that this is
an otherwise unneeded workaround for comiplers.  Your suggested
title instead hints that it is wrong to assume that errno will be
set to non-zero after a syscall.  I do not think that is the message
we want to send to our readers.

Right, the oneline I suggested was only for the original patch, with which
I disagreed.

I actually do not know how your rewrite could be better, though.

		/* GCC thinks socket()/connect() might fail to set errno */
		return errno ? errno : EIO;

If a compiler thinks errno may *not* be set, can 'errno' be reliably
used to decide if it can be returned as-is or a fallback value EIO
should be used, without triggering the same (incorrect) working in
the first place?

Oh, I guess I mistook the problem for something else, then.

If the problem is that `errno` is not set in case of failure, the
resolution is easy (and even recommended in the manual page of `errno`):
simply set it to 0 before the syscall (or in the function that relies on
`errno == 0` means success).

There is really no need to introduce a `saved_errno` variable (which to me
would suggest that we need to save the current value of `errno` and
reinstate it later, as we do sometimes e.g. when we call `close()` after
noticing an error whose `errno` we need to preserve for the caller).

Ciao,
Dscho