fstReaderOpen failed for temporary FST file

[avelure]

I get
** Fatal: 1050ns+3: fstReaderOpen failed for temporary FST file
when trying to create a VCD file with the command
nvc --std=08 -e test-beh -r -w --format=vcd

I get a temp.fst file and a test-beh.vcd, however the vcd file is empty.

[nickg]

I couldn't reproduce this (but I only used a simple test case). Can you try running the fst2vcd program that comes with GtkWave on the temp.fst file and see if that gives any error?

[avelure]

It was the same reproducer as in #614.
fst2vcd has no problems converting it and both fst and vcd shows fine in gtkwave.

[erick166]

I've tried generating a VCD file using the "-w --format=vcd" arguments, but the file appears to be empty.
It works however if I use "--format=fst", any ideas why?

[nickg]

@erick166 are you using Windows as well? The VCD writer is actually just the FST writer with an extra step where it writes the FST to a temporary file and then does the equivalent of fst2vcd on it.

[erick166]

Yes, I'm using Windows.

[nickg]

I'm still unable to reproduce this (trying MinGW x64 build in a Windows 10 VM). Does it happen reliably with any design you try? @erick166 did you get the same "fstReaderOpen failed for temporary FST file" as in the first message?

[erick166]

Yes, it happens with different testbenches and I also get the same message. Could it maybe be something in the file path separators for the temporary file?

[nickg]

I managed to reproduce it: it works fine in MSYS2 MingW x64 but not UCRT x64 (and I guess Clang x64 too since it uses the same libc).

[nickg]

The problem seems to be a difference in behaviour under UCRT in GtkWave's fstapi.c library that we import. I'm still not sure I understand what's going on but I pushed a workaround that fixes it for me. Could you test again?

[erick166]

I tested with the fix and it works for me as well, thanks!

[avelure]

I can confirm I was likely using either ucrt64 or clang64 at the time.

[nickg]

Thanks for testing. I submitted a slightly improved fix to GtkWave in gtkwave/gtkwave#376.