On 19/09/2025 10:21 pm, Baesken, Matthias wrote:
Hi David, even on RHEL 7.9 it works without adding -lrt to linking ,
see the example :
It is only pre glibc 2.17 that we need librt.so for.
David
gcc --version
gcc (GCC) 4.8.5 20150623 (Red Hat 4.8.5-44)
Copyright (C) 2015 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.
gcc clock_gettime.c -o clock_gettime
./clock_gettime
Elapsed time: 2.008803 seconds
more ./clock_gettime.c
#include <stdio.h>
#include <time.h>
#include <unistd.h>
int main() {
struct timespec start, end;
double elapsed;
// Get start time
clock_gettime(CLOCK_MONOTONIC, &start);
// Simulate some work (sleep for 2 seconds)
sleep(2);
// Get end time
clock_gettime(CLOCK_MONOTONIC, &end);
// Calculate elapsed time in seconds (as a double)
elapsed = (end.tv_sec - start.tv_sec);
elapsed += (end.tv_nsec - start.tv_nsec) / 1e9;
printf("Elapsed time: %.6f seconds\n", elapsed);
return 0;
}
ldd --version
ldd (GNU libc) 2.17
But on ancient SLES 11 (SUSE Linux 11) with
ldd --version
ldd (GNU libc) 2.11.3
I see the issue , there I have to add -lrt :
gcc clock_gettime.c -o clock_gettime
/tmp/ccU07fSz.o: In function `main':
clock_gettime.c:(.text+0x20): undefined reference to `clock_gettime'
clock_gettime.c:(.text+0x40): undefined reference to `clock_gettime'
collect2: ld returned 1 exit status
gcc clock_gettime.c -o clock_gettime -lrt
./clock_gettime
Elapsed time: 2.000108 seconds
So it seems we have to go back to SLES11 and RHEL 6 (!) for this strange
librt issue .
Best regards, Matthias
-----Original Message-----
From: Baesken, Matthias
Sent: Friday, 19 September 2025 09:42
To: 'David Holmes' <[email protected]>; [email protected]; hotspot-dev
<[email protected]>
Cc: Langer, Christoph <[email protected]>
Subject: RE: "useless" librt.so.1 dependency on Linux reported by dpkg-shlibdeps
Hi David, I found a RHEL 7.9 machine with an old glibc :
ldd --version
ldd (GNU libc) 2.17
But the gcc on this machine is 4.8.5 , probably too old to build OpenJDK
there to see if this change breaks something .
Any idea what I should test on this old machine regarding librt.so.1 ?
Best regards, Matthias
( seems some versions of RHEL 7 / SLES 12 still had those old glibc
versions)
Could we clean this up?
Or is there still some need to support this in jdk26 ?
I always find it very difficult to determine when checks like these
become unnecessary. I think RHEL 7 with glibc 2.17 is the oldest Linux
release we currently support.
Given I wrote the above in April 2021, I would hope we can now move on,
but again I don't know how to readily determine that.
I could create a removal PR and maybe you can test on the oldest platforms you
want to support in release 26 ?
I don't have access to such systems for testing.
David
