[PATCH 04/12] Makefile: remove NEEDS_LIBRT build variable

Ramsay Jones· Mar 15, 2025, 02:47 UTC · lore

Commit d19e3a5b21 ("Makefile: add NEEDS_LIBRT to optionally link with librt", 2016-07-07) introduced the NEEDS_LIBRT build variable to disassociate the HAVE_CLOCK_GETTIME variable with the unconditional linking of the librt library. At one time, the clock_gettime() function was not available as part of the libc library and (on some unix systems) required linking with librt.

Commit 52fcec75ce ("config.mak.uname: define NEEDS_LIBRT under Linux, for now", 2016-07-10) set the NEEDS_LIBRT variable in the Linux section of the config.mak.uname file, since Debian 7 (wheezy) was one of the few remaining distributions, with glibc 2.13, that required linking with librt for clock_gettime(). Note that from glibc version 2.17, this is no longer necessary.

Note that Debian 7.0 was released on May 4th, 2013 and benefited from long term support until May 2018 when it went end-of-life. Since that time, Linux distributions use a more up-to-date library, for example:

    Distribution   version  end of support

    Debian 8       2.19     30th June 2020
    RHEL   8       2.28     31st May  2024 *
    Ubuntu 16.04   2.23     30th Apr  2021

* paid 'Maintenance support' ends 31st May 2029

Since it is no longer required, remove NEEDS_LIBRT from the Makefile and config.mak.uname.

Signed-off-by: Ramsay Jones <ramsay@ramsayjones.plus.com>
---
 Makefile         | 7 -------
 config.mak.uname | 2 --
 2 files changed, 9 deletions(-)

Show changes to 2 files +0 −9

Makefile, config.mak.uname

diff --git a/Makefile b/Makefile
index 818dde32a9..8fa4d2664e 100644
--- a/Makefile
+++ b/Makefile
@@ -340,9 +340,6 @@ include shared.mak
 #
 # Define HAVE_SYNC_FILE_RANGE if your platform has sync_file_range.
 #
-# Define NEEDS_LIBRT if your platform requires linking with librt (glibc version
-# before 2.17) for clock_gettime and CLOCK_MONOTONIC.
-#
 # Define HAVE_BSD_SYSCTL if your platform has a BSD-compatible sysctl function.
 #
 # Define HAVE_GETDELIM if your system has the getdelim() function.
@@ -2171,10 +2168,6 @@ ifdef HAVE_SYNC_FILE_RANGE
 	BASIC_CFLAGS += -DHAVE_SYNC_FILE_RANGE
 endif
 
-ifdef NEEDS_LIBRT
-	EXTLIBS += -lrt
-endif
-
 ifdef HAVE_BSD_SYSCTL
 	BASIC_CFLAGS += -DHAVE_BSD_SYSCTL
 endif
diff --git a/config.mak.uname b/config.mak.uname
index b12d4e168a..88007c4f13 100644
--- a/config.mak.uname
+++ b/config.mak.uname
@@ -54,8 +54,6 @@ ifeq ($(uname_S),Linux)
 	HAVE_DEV_TTY = YesPlease
 	HAVE_CLOCK_GETTIME = YesPlease
 	HAVE_CLOCK_MONOTONIC = YesPlease
-	# -lrt is needed for clock_gettime on glibc <= 2.16
-	NEEDS_LIBRT = YesPlease
 	HAVE_SYNC_FILE_RANGE = YesPlease
 	HAVE_GETDELIM = YesPlease
 	FREAD_READS_DIRECTORIES = UnfortunatelyYes

-- 
2.49.0

patch, 12 partsMakefile: remove NEEDS_LIBRT build variable