GNU bug report logs - #37795
26.1; Fixnum overflow on dpyinfo->last_user_time

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Message #10 received at 37795-done <at> debbugs.gnu.org (full text, mbox):

From: Paul Eggert <eggert <at> cs.ucla.edu>
To: Stefan Monnier <monnier <at> iro.umontreal.ca>
Cc: 37795-done <at> debbugs.gnu.org
Subject: re: 26.1; Fixnum overflow on dpyinfo->last_user_time
Date: Fri, 18 Oct 2019 13:33:06 -0700

[Message part 1 (text/plain, inline)]

Thanks for reporting that. I installed the attached patches, which are 
along the lines that you suggested. They also fix a similar bug in 
xterm.c's x_ewmh_activate_frame.

> I also see other places where we do:
> 
>     selection_data = list4 (selection_name, selection_value,
> 			    INT_TO_INTEGER (timestamp), frame);
> 
> so maybe we should be using `INT_TO_INTEGER` rather than `make_int`?

Yes for Time values, since Time might be (usually is?) unsigned and 
might exceed INTMAX_MAX. However, list1i etc. accept signed integers so 
make_int is fine for them.

Changing list1i etc. to use intmax_t and make_int is a small performance 
hit in some cases, but is probably worth it given the reliability 
implications of ignoring integer overflow.

> AFAICT the exact value of those timestamps doesn't really matter,

Some Emacs code subtracts Time values and assumes wraparound overflow, 
so if we shoehorn them into fixnums we would need to take that into 
account. Probably better to leave things be.

[0001-Fix-integer-overflow-bug-in-Time-conversion.patch (text/x-patch, attachment)]

[0002-Generalize-list1i-etc.-to-all-signed-integer-types.patch (text/x-patch, attachment)]

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