On Thu, Jan 5, 2023 at 10:33 PM Jacob Bachmeyer <jcb62...@gmail.com> wrote:
>
> NightStrike wrote:
> > On Fri, Dec 23, 2022 at 11:00 PM Jacob Bachmeyer <jcb62...@gmail.com> wrote:
> >
> >> NightStrike wrote:
> >>
> >>> On Wed, Dec 21, 2022 at 11:37 PM Jacob Bachmeyer <jcb62...@gmail.com>
> >>> wrote:
> >>>
> >>>> [...]
> >>> So at least we know for sure that this particular instance of extra
> >>> characters is coming from Wine. Maybe Wine can be smart enough to
> >>> only translate \n into \r\n instead of translating \r\n into \r\r\n.
> >>> Jacek / Eric, comments here? I'm happy to try another patch, the
> >>> first one was great.
> >>>
> >>>
> >> I doubt that Wine is doing that translation. MinGW libc produces output
> >> conformant to Windows conventions, so printf("\n") on a text handle
> >> emits "\r\n", which Wine passes along. POSIX convention is that "\n" is
> >> translated to "\r\n" in the kernel terminal driver upon output, so the
> >> kernel translates the "\n" in the "\r\n" into /another/ "\r\n", yielding
> >> "\r\r\n" at the pty master end. This is why DejaGnu testsuites must be
> >> prepared to discard excess carriage returns. The first CR came from
> >> MinGW libc; the second CR came from the kernel terminal driver; the LF
> >> was ultimately passed through.
> >>
> >
> > Jacek and I have been digging into this on IRC, and he's been very
> > helpful in trying to get further, but we're still stuck. We tried to
> > be more introspective, inserting strace both as "strace script wine"
> > and as "script strace wine". We tried running just "wine a.exe"
> > without any extra glue, and logging the raw SSH packets from putty.
> > After many iterations on these and other tests, Jacek finally had the
> > idea to try removing Windows entirely from the equation, and we ran
> > with a purely unix program / compiler combination:
> >
> > #include <unistd.h>
> >
> > int main()
> > {
> > write(1, "test\r\n", 6);
> > return 0;
> > }
> >
> > (and also as "test\n", 5)
> >
> > In both versions, the following was observed:
> >
> > case 1) ./a.out | xxd
> > case 2) script -c ./a.out out; xxd out
> > case 3) enable putting logging, ./a.out
> >
> > In case 1, xxd showed no extra \r's. In cases 2 and 3, there was an
> > extra \r (either 0d 0d 0a for test\r\n, or 0d 0a for test\n).
> >
> > So, is it possible after all of this back and forth regarding mingw,
> > wine, and others, that it's down to the write() system call that's
> > inserting extra \r's? Is this expected?
> >
>
> "This is why DejaGnu testsuites must be prepared to discard excess
> carriage returns."
>
> The write(2) system call inserts nothing and simply hands off the buffer
> to the relevant part of the kernel I/O subsystem. (The kernel in POSIX
> is *not* a monolithic black box.) When stdout for your test program is
> a pty slave, that relevant part is the kernel terminal driver. The
> kernel terminal driver is converting "\n" to "\r\n" upon output to the
> associated port, since hardware terminals typically *do* require CRLF.
> The associated port in this case is virtual and part of the kernel pty
> subsystem, which presents octets written to that port to its associated
> pty master device. The user-visible pty slave device acts just like a
> serial terminal, including all translations normally done for handling
> serial terminals.
>
> A pty is conceptually a null-modem cable connected between two
> infinitely-fast serial ports on the same machine, although the slave
> will still report an actual baud rate if queried. (Run "stty" with no
> arguments under script(1), an ssh session, or an X11 terminal emulator
> to see what a pty slave looks like on your machine.)
>
> In your case 1, the pty subsystem is not used and output is collected
> over a pipe. Using "./a.out > out; xxd out" would produce the same
> results. In cases 2 and 3, there is a pty involved, either set up by
> script(1) or by sshd (assuming you meant "enable putty logging" in case
> 3) that performs the standard terminal translations. In all cases,
> strace(1) will show the exact string written to the pty slave device,
> which will not include any extra CRs because *those* *are* *inserted*
> *by* *the* *kernel* *terminal* *driver* as the data is transferred to
> the pty master device's read queue.
>
> This insertion of carriage returns is expected and standardized behavior
> in POSIX and is the reason Unix could use bare LF as end-of-line even
> though hardware terminals always needed CRLF. CP/M (and therefore
> MS-DOS which began its existence as a cheap CP/M knockoff) did not have
> this translation layer and instead dumped the complexity of a two-octet
> end-of-line sequence on user programs, leading to much confusion even
> today. This is not a Wine issue, although the terminal escape sequences
> in your original issue *were* from Wine. Note that the number of excess
> carriage returns that a DejaGnu testsuite must be prepared to discard is
> unspecified because running tests on remote targets may result in *any*
> *number* of CRs preceding each LF by the time the results reach the test
> driver machine in more complex testing lab environments.
First, I just want to thank you for your patience. You are putting a
lot of effort into these replies, and it is appreciated.
I did another little test to try to better understand your point. I
ran a linux native testsuite under a simulator that just sets SIM to "
". This resulted in extra ^M's also, although many tests pass because
they're already looking for \r\n to accommodate windows. So I think
I've come around to grasp what you've been heroically re-explaining...
So if we have to modify every test in the entire testsuite to check
for zero or more \r's followed by zero or more \n's, would it be
better to add a dg-output-line proc that does this automatically
everywhere? I feel like changing every output pattern test won't be
too maintainable. You had mentioned previously modifying ${tool}_load
to filter out extra \r's, but I couldn't see where or how to do that.
For completeness, setting a random selection of tests to look for
\r*\n? worked (this would cover even deprecated systems that only use
CR as well as flagging the weird rust case of \r\r\n\n as bad).
