Compilation Error, Debian/12

[manchelsi]

Distr: Debian Bookworm
Kernel: 6.1.0

Compilation Error:

make -C /lib/modules/6.1.0-7-amd64/build/ M=/usr/local/src/ipt-ratelimit modules
make[1]: Entering directory '/usr/src/linux-headers-6.1.0-7-amd64'
  CC [M]  /usr/local/src/ipt-ratelimit/xt_ratelimit.o
/usr/local/src/ipt-ratelimit/xt_ratelimit.c: In function ‘parse_rule’:
/usr/local/src/ipt-ratelimit/xt_ratelimit.c:530:37: warning: this statement may fall through [-Wimplicit-fallthrough=]
  530 |                                 val = val / 8 + (val / 8 / 2);
      |                                 ~~~~^~~~~~~~~~~~~~~~~~~~~~~~~
/usr/local/src/ipt-ratelimit/xt_ratelimit.c:532:25: note: here
  532 |                         case 1:
      |                         ^~~~
/usr/local/src/ipt-ratelimit/xt_ratelimit.c:534:37: warning: this statement may fall through [-Wimplicit-fallthrough=]
  534 |                                 val *= 2;
      |                                 ~~~~^~~~
/usr/local/src/ipt-ratelimit/xt_ratelimit.c:536:25: note: here
  536 |                         case 2:
      |                         ^~~~
  MODPOST /usr/local/src/ipt-ratelimit/Module.symvers
  CC [M]  /usr/local/src/ipt-ratelimit/xt_ratelimit.mod.o
  LD [M]  /usr/local/src/ipt-ratelimit/xt_ratelimit.ko
  BTF [M] /usr/local/src/ipt-ratelimit/xt_ratelimit.ko
Skipping BTF generation for /usr/local/src/ipt-ratelimit/xt_ratelimit.ko due to unavailability of vmlinux
make[1]: Leaving directory '/usr/src/linux-headers-6.1.0-7-amd64'
sync
gcc -O2 -Wall -Wunused -fPIC   -o libxt_ratelimit_sh.o -c libxt_ratelimit.c
gcc -shared -o libxt_ratelimit.so libxt_ratelimit_sh.o
/usr/bin/ld: libxt_ratelimit_sh.o: in function `_init':
libxt_ratelimit.c:(.text+0x210): multiple definition of `_init'; /usr/lib/gcc/x86_64-linux-gnu/12/../../../x86_64-linux-gnu/crti.o:(.init+0x0): first defined here
collect2: error: ld returned 1 exit status
make: *** [Makefile:19: libxt_ratelimit.so] Error 1
rm libxt_ratelimit_sh.o

[manchelsi]

Fix builds on iptables version 1.8.9 or newer
Ever since iptables commit ef108943f69a6e20533d58823740d3f0534ea8ec,
the _init macro has become guarded by XTABLES_INTERNAL, thus breaking
this extension.

Explicitly specify the constructor attribute on the initialization
function, which works on all versions.

diff --git a/libxt_ratelimit.c b/libxt_ratelimit.c                                                                                           
index d1a03d7..f3ecd6d 100644                                                                                                                
--- a/libxt_ratelimit.c                                                                                                                      
+++ b/libxt_ratelimit.c                                                                                                                      
@@ -153,7 +153,7 @@ static struct xtables_match ratelimit_mt_reg[] = {                                                                       
        },
 };

-void _init(void)                                                                                                                            
+static void __attribute__((constructor)) _init(void)                                                                                        
 {
        xtables_register_matches(ratelimit_mt_reg, ARRAY_SIZE(ratelimit_mt_reg));
 }

[manchelsi]

#27