Format file differences (was: Re: pdflatex does not work on win after todays update but does on linux)

[Jonathan Fine]

Hi Andreas

You wrote

On a multiplatform installation all format-files are stored
> under /texmf-var/web2c without any further directories for different OS
>

 This is useful information. It shows that TeX-Live assumes that format
files are platform independent. As Karl has responsibility for both
TeX-Live and pdftex, it may be correct to say that this platform
independence is an undocumented feature.

I'm now going to make a wild guess. Even if wrong, the thinking leading up
to the guess might be helpful. In the file web2c/pdftexdir/ptexmac.h
C-language macros dumpcharptr(a) and undumpcharptr(s) are defined. They
were added on 20 Jan 2021. I suggest looking for an error in these macros,
or in the use of these macros.

The following monster URL will bring up for you the definitions.
https://github.com/tex-mirror/pdftex/commit/70e0c9c9e95184665909dd447bc80aa08d700822#diff-0561d129eac29b0ac46df3edb18316f19ae0ea758bd8ce890f91e9f2f097a84eR223-R245

In case it's helpful, here's how I found these macro definitions.

1. I cloned https://github.com/tex-mirror/pdftex onto my PC.
2. On my PC, I grepped for WIN, returning only a list of file names.
3. I filtered to get only the .h file names. There were 47.
4. I eyeballed those file names. The following were the only ones in web2c.
source/src/texk/web2c/pdftexdir/ptexmac.h
source/src/texk/web2c/pdftexdir/ptexlib.h
source/src/texk/web2c/texmfmp.h
source/src/texk/web2c/w2c/config.h
source/src/texk/web2c/texmfmp-help.h
source/src/texk/web2c/synctexdir/synctex_parser_utils.h
source/src/texk/web2c/cpascal.h
5. On github I looked at the history of web2c/pdftexdir/ptexmac.h
6. This gave as the most recent change a commit
karl sync with tl 57477, for (un)dump of \pdfglyphtounicode
7. BINGO. That (un)dump looks like the addition of a new feature.
8. Here's the diff for the commit
https://github.com/tex-mirror/pdftex/commit/70e0c9c9e95184665909dd447bc80aa08d700822
9. From there the rest is easy. Just search or eyeball for the string
"dump".

Finally, and perhaps irrelevant, Google and Facebook have lately detected
"recidivist machines". Further, "These machines were credibly accused of
corrupting multiple different stable well-debugged large-scale
applications. Each machine was accused repeatedly by independent teams but
conventional diagnostics found nothing wrong with them."

Further in one case "Google's errant hardware conducted what might be
described as an auto-erratic ransomware attack." Further "One of our
mercurial cores corrupted encryption. It did it in such a way that only it
could decrypt what it had wrongly encrypted."

You can read more here:
https://www.theregister.com/2021/06/04/google_chip_flaws/

So how is this related to the cross-platform dump / undump problem? Perhaps
both the Windows and Linux versions are correct in that they can undump
what they dump. So single platform testing will not detect the error.
Indeed there is no error, until either the dump is sufficiently documented,
or until cross platform behaviour is required and tested.

I hope this helps.
-- 
Jonathan
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