On time64 and Large File Support

[Paul Eggert]

On 2022-11-11 20:20, Wookey wrote:
> It doesn't seem right to me that AC_SYS_LARGEFILE should imply
> AC_SYS_YEAR2038. What is the reasoning behind that?

First, in Autoconf git AC_SYS_LARGEFILE does not imply AC_SYS_YEAR2038. 
The former is willing to fall back on 32-bit time_t if 64-bit is not 
available. The latter errors out unless 64-bit time_t is available.

Second and to answer your question, the intent of AC_SYS_LARGEFILE has 
always been, "I want open, stat, lseek, etc. to work on all files, and I 
don't want them to fail with errno==EOVERFLOW simply because my integer 
types are too narrow".

For this to work with glibc 2.34+ on x64 and arm GNU/Linux, time_t must 
be 64 bits just as off_t, dev_t etc must be 64 bits; otherwise syscalls 
like 'stat' stop working on some files. These failures can have security 
implications. Many software developers, even in the security arena, 
haven't thought through the implications of EOVERFLOW and their programs 
do the wrong thing with EOVERFLOW.