Compilation of earthtrack fails on Debian 11 'Bullseye'

[lrowen]

lowen@lowen-7740:~/development/predict/predict-2.3.0/clients/earthtrack$ gcc --version
gcc (Debian 10.2.1-6) 10.2.1 20210110
Copyright (C) 2020 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.

Using the default build script in the 2.3.0 distribution, I get the following error:

lowen@lowen-7740:~/development/predict/predict-2.3.0/clients/earthtrack$ ./build
Compiling earthtrack... /usr/bin/ld: /tmp/cckldGDS.o: in function `arccos':
earthtrack.c:(.text+0x32a): undefined reference to `acos'
/usr/bin/ld: earthtrack.c:(.text+0x359): undefined reference to `acos'
/usr/bin/ld: /tmp/cckldGDS.o: in function `rangecircle':
earthtrack.c:(.text+0x4ce): undefined reference to `sincos'
/usr/bin/ld: earthtrack.c:(.text+0x4f7): undefined reference to `sincos'
/usr/bin/ld: earthtrack.c:(.text+0x536): undefined reference to `cos'
/usr/bin/ld: earthtrack.c:(.text+0x54c): undefined reference to `asin'
/usr/bin/ld: earthtrack.c:(.text+0x55d): undefined reference to `sincos'
/usr/bin/ld: earthtrack.c:(.text+0x5f5): undefined reference to `acos'
/usr/bin/ld: earthtrack.c:(.text+0x83b): undefined reference to `acos'
collect2: error: ld returned 1 exit status
earthtrack compilation failed!  :-(

Changing the compile line in the build script from:
cc -O3 -s -fomit-frame-pointer -lm earthtrack.c -o earthtrack
to
cc -O3 -s -fomit-frame-pointer earthtrack.c -o earthtrack -lm
fixed the issue.

From the gcc link options page:

-llibrary
-l library
...
It makes a difference where in the command you write this option; the linker searches and processes libraries and object files in the order they are specified. Thus, ‘foo.o -lz bar.o’ searches library ‘z’ after file foo.o but before bar.o. If bar.o refers to functions in ‘z’, those functions may not be loaded.

So the -lm needs to come last in the line, with 'modern' gcc.

[frrobert2]

I had the same issue with Ubuntu 22.04. The suggested fix above fixed the issue.