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Re: On time64 and Large File Support

From: Paul Eggert
Subject: Re: On time64 and Large File Support
Date: Sun, 25 Dec 2022 11:19:11 -0800
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:102.0) Gecko/20100101 Thunderbird/102.4.2

On 11/12/22 21:11, Zack Weinberg wrote:
"A couple hours" more like eight, ugh.

I know the feeling. I didn't get time free until recently.

I reviewed your patch and had the following thoughts.

* Gnulib doesn't need AC_SYS_LARGEFILE_REQUIRED or AC_SYS_YEAR2038_REQUIRED and they're easy for users to do on their own with a simple AS_IF, so let's omit these variants for now, to keep things simpler.

* The documentation incorrectly implies that AC_SYS_LARGEFILE and AC_SYS_YEAR2038 are orthogonal, i.e., that one can request large-file support and year-2038 support independently. But AC_SYS_YEAR2038 AC_REQUIREs AC_SYS_LARGEFILE, and one cannot configure with --disable-largefile --enable-year2038 and expect things to work. This is inherent to the underlying _TIME_BITS mechanism; it's not something Autoconf can fix with glibc, and since this year-2038 business only occurs with glibc it's not something Autoconf can (or is likely to be able to) fix anywhere.

To help things move forward I installed your patch into Autoconf master on Savannah, and followed up with the attached patch which tries to address the above issues. In particular, it notes that the difference between AC_SYS_LARGEFILE and AC_SYS_YEAR2038 is a temporary hack, in that eventually (hopefully well before the year 2038) AC_SYS_LARGEFILE will be an alias for what AC_SYS_YEAR2038 does now.

Comments welcome of course.

I tested this by migrating these Autoconf changes into my private copy of Gnulib and gzip, and building gzip on both 32- and 64-bit glibc. I plan to install those changes on Savannah soon, and to follow up with similar changes to GNU coreutils etc. This should help to test these Autoconf changes before the next Autoconf is released.

Attachment: 0001-Omit-just-added-_REQUIRED-macros.patch
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