SWI osExit takes a status in A, and the shell keeps it. Fifty eight exits
across twenty three programs now say deliberately whether they worked: 25
did what they were asked, 24 did not, 9 were asked wrongly. Compare is the
exception and says so - one there means the files differ, which is a result
rather than a failure, the way diff has always had it.
IN A RATHER THAN Q, which is not a departure from the rule that a service
answers in Q. This one takes an ARGUMENT, the way osPrintNumber takes A and
B, and it never returns to answer anything. A is free precisely because a
return would have put it back - and Q is the ALU's output, so a small
number costs four instructions there against one in A.
The shell does not print it. A program that failed has already said so in
words and a number beside that is noise, so osLastStatus hands it back and
Status is the program that shows it. That indirection is the point: the
number exists for the thing that cannot read words.
MARKING THE EXITS FOUND A DEFECT ON THE FIRST RUN. Type and More printed
why they had failed and then fell through into the success exit, reporting
that all was well. Nobody had noticed, because while the only reader was a
person, the person could see both the complaint and the claim.
Two smaller things. Snake sets the console to line mode and then exits with
zero, and the linter flagged the second RSTA as redundant - an exit status
and a console mode, equal by accident, which is the class that must never
be collapsed. And the README still taught answering by writing into the
frame, three months of habit that SRET replaced yesterday; that section is
gone and the one describing SRET stands in its place.
osFileStart sets an extent aside and osFileWrite refuses a block index outside
it, so writing off the end was already barred. Committing a larger size was
not, and reaches the same neighbour by simply claiming it: a directory entry is
the only record of what a file owns, so an entry claiming a block it was never
given owns it, and so does whatever owned it before. Both files then look
perfectly well formed. The free count went backwards past zero on the same
path.
Found by ChatGPT's review of the streaming work, in NOTES.md. I had bounded the
index because writing off the end was the obvious way to reach a neighbour, and
had not noticed that the other end of the same reservation was open.
THE SIZE IS COMPARED, NOT THE ROOM IT TAKES UP. One block and a tail occupies
exactly what two whole blocks occupy, so bounding the blocks alone would let a
file reserve the first, commit the second, claim no block it was not given, and
still report two hundred and forty six bytes that were never written to it -
whatever the disk had there before.
Checked before anything is touched, which is why the temporary is found twice.
The old file is deleted a few lines down and a refusal after that point would
have destroyed the thing it was protecting.
AND IT CAUGHT A REAL ONE IMMEDIATELY. The assembler reserves the file plus room
for its vectors, and asked for four bytes per vector DECLARED - which looks like
a safe bound and is not, because a device is declared during the SECOND pass, in
the line that implements it. A program with a device installs a vector that was
not counted when the room was measured. CosmOS reserved 14,163 bytes and
committed 14,167, writing four bytes past what it had been given on every build
since S2. It landed inside the last block it owned, and would not have if the
boundary had fallen four bytes earlier.
It reserves against the vector table's LIMIT now, which cannot go stale whenever
things are counted.
Claim.asm is the program that tries it: reserve one block and a tail of ten,
write them, then tell osFileDone the file came to two whole blocks. The refusal
and the honest commit that follows are both recorded.
Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01E2JrLzFvuFX9fgi1LDRjrW
Anachronaut
