portability: `clock_gettime` needs `-lrt` on Linux

[katef]

portability: `clock_gettime` needs `-lrt` on Linux

[katef]

Which libc is this?

[silentbicycle]

The default libc on Void, probably glibc. I've never tried to change it.

[katef]

Curious. I don't see the same on debian:

; ldd gh/libfsm/build/bin/fsm                            
        linux-vdso.so.1 (0x00007ffefabd3000)
        libc.so.6 => /lib/x86_64-linux-gnu/libc.so.6 (0x00007fdbc05a8000)
        /lib64/ld-linux-x86-64.so.2 (0x00007fdbc07c5000)
; /lib/x86_64-linux-gnu/libc.so.6                        
GNU C Library (Debian GLIBC 2.28-8) stable release version 2.28.
Copyright (C) 2018 Free Software Foundation, Inc.
This is free software; see the source for copying conditions.
There is NO warranty; not even for MERCHANTABILITY or FITNESS FOR A
PARTICULAR PURPOSE.
Compiled by GNU CC version 8.3.0.
libc ABIs: UNIQUE IFUNC ABSOLUTE
For bug reporting instructions, please see:
<http://www.debian.org/Bugs/>.
; objdump -T /lib/x86_64-linux-gnu/libc.so.6 | grep clock_gettime
0000000000107360 g    DF .text  000000000000006d  GLIBC_PRIVATE __clock_gettime
0000000000107360  w   DF .text  000000000000006d  GLIBC_2.17  clock_gettime

[silentbicycle]

According to the Linux man page for clock_gettime:

Link with -lrt (only for glibc versions before 2.17).

and glibc 2.17 is from 2013 or so. I've run into broken builds due to this within the last 5 or so years, probably because of systems that were still running older versions of glibc. It was something I encountered a couple times in CI, oddly enough.