fix problem which don't support 1-byte atomic instructions natively on RISCV64 architecture

[jiangxiaobin96]

When building on RISCV64 architecture, I met the following error.

/usr/bin/ld: src/cfgparse.o: in function `check_config_validity':
/home/haproxy/src/cfgparse.c:2476: undefined reference to `__atomic_exchange_1'
/usr/bin/ld: src/dns.o: in function `dns_resolve_send':
/home/haproxy/src/dns.c:313: undefined reference to `__atomic_fetch_sub_1'
/usr/bin/ld: /home/haproxy/src/dns.c:354: undefined reference to `__atomic_fetch_add_1'
/usr/bin/ld: /home/haproxy/src/dns.c:304: undefined reference to `__atomic_fetch_add_1'
/usr/bin/ld: src/dns.o: in function `dns_session_io_handler':
/home/haproxy/src/dns.c:726: undefined reference to `__atomic_fetch_sub_1'
/usr/bin/ld: /home/haproxy/src/dns.c:713: undefined reference to `__atomic_fetch_add_1'
/usr/bin/ld: src/dns.o: in function `b_getblk':
/home/haproxy/include/haproxy/buf.h:328: undefined reference to `__atomic_fetch_add_1'
/usr/bin/ld: src/dns.o: in function `pool_free':
/home/haproxy/include/haproxy/pool.h:291: undefined reference to `__atomic_fetch_add_1'
/usr/bin/ld: src/dns.o: in function `__pool_alloc':
/home/haproxy/include/haproxy/pool.h:246: undefined reference to `__atomic_fetch_sub_1'
/usr/bin/ld: src/dns.o: in function `pool_free':
/home/haproxy/include/haproxy/pool.h:291: undefined reference to `__atomic_fetch_add_1'
/usr/bin/ld: src/dns.o: in function `dns_process_req':
/home/haproxy/src/dns.c:1196: undefined reference to `__atomic_fetch_add_1'
/usr/bin/ld: src/sink.o: in function `sink_forward_oc_io_handler':
/home/haproxy/src/sink.c:515: undefined reference to `__atomic_fetch_sub_1'
/usr/bin/ld: /home/haproxy/src/sink.c:549: undefined reference to `__atomic_fetch_add_1'
/usr/bin/ld: /home/haproxy/src/sink.c:549: undefined reference to `__atomic_fetch_add_1'
/usr/bin/ld: /home/haproxy/src/sink.c:501: undefined reference to `__atomic_fetch_add_1'
/usr/bin/ld: src/sink.o: in function `sink_forward_io_handler':
/home/haproxy/src/sink.c:375: undefined reference to `__atomic_fetch_sub_1'
/usr/bin/ld: src/sink.o: in function `b_peek_ofs':
/home/haproxy/include/haproxy/buf.h:142: undefined reference to `__atomic_fetch_add_1'
/usr/bin/ld: /home/haproxy/include/haproxy/buf.h:143: undefined reference to `__atomic_fetch_add_1'
/usr/bin/ld: /home/haproxy/include/haproxy/buf.h:143: undefined reference to `__atomic_fetch_add_1'
/usr/bin/ld: src/ring.o: in function `ring_detach_appctx':
/home/haproxy/src/ring.c:240: undefined reference to `__atomic_fetch_sub_1'
/usr/bin/ld: src/ring.o: in function `cli_io_handler_show_ring':
/home/haproxy/src/ring.c:320: undefined reference to `__atomic_fetch_sub_1'
/usr/bin/ld: /home/haproxy/src/ring.c:354: undefined reference to `__atomic_fetch_add_1'
/usr/bin/ld: /home/haproxy/src/ring.c:354: undefined reference to `__atomic_fetch_add_1'
/usr/bin/ld: /home/haproxy/src/ring.c:311: undefined reference to `__atomic_fetch_add_1'
collect2: error: ld returned 1 exit status
make: *** [Makefile:933: haproxy] Error 1

It seems the target platform doesn't support 1-byte atomic instructions natively. So I add -latomic to support when compiling.
The result:

[root@master0 haproxy]# ./haproxy
HAProxy version 2.5-dev13-47940c-45 2021/11/10 - https://haproxy.org/
Status: development branch - not safe for use in production.
Known bugs: https://github.com/haproxy/haproxy/issues?q=is:issue+is:open
Running on: Linux 5.4.61 #20 SMP Thu Aug 26 11:50:01 CST 2021 riscv64
Usage : haproxy [-f <cfgfile|cfgdir>]* [ -vdVD ] [ -n <maxconn> ] [ -N <maxpconn> ]
        [ -p <pidfile> ] [ -m <max megs> ] [ -C <dir> ] [-- <cfgfile>*]
        -v displays version ; -vv shows known build options.
        -d enters debug mode ; -db only disables background mode.
        -dM[<byte>] poisons memory with <byte> (defaults to 0x50)
        -V enters verbose mode (disables quiet mode)
        -D goes daemon ; -C changes to <dir> before loading files.
        -W master-worker mode.
        -q quiet mode : don't display messages
        -c check mode : only check config files and exit
        -cc check condition : evaluate a condition and exit
        -n sets the maximum total # of connections (uses ulimit -n)
        -m limits the usable amount of memory (in MB)
        -N sets the default, per-proxy maximum # of connections (0)
        -L set local peer name (default to hostname)
        -p writes pids of all children to this file
        -de disables epoll() usage even when available
        -dp disables poll() usage even when available
        -dS disables splice usage (broken on old kernels)
        -dG disables getaddrinfo() usage
        -dR disables SO_REUSEPORT usage
        -dr ignores server address resolution failures
        -dV disables SSL verify on servers side
        -dW fails if any warning is emitted
        -dD diagnostic mode : warn about suspicious configuration statements
        -sf/-st [pid ]* finishes/terminates old pids.
        -x <unix_socket> get listening sockets from a unix socket
        -S <bind>[,<bind options>...] new master CLI

My Platform:

[root@master0 haproxy]# uname -a
Linux master0 5.4.61 #20 SMP Thu Aug 26 11:50:01 CST 2021 riscv64 riscv64 riscv64 GNU/Linux

GCC version:

gcc (GCC) 9.3.1
Copyright (C) 2019 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.

[lukastribus]

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[wtarreau]

This could have broken other platforms and environments missing libatomic. I've addressed it differently by checking whether or not gcc reports the need for libatomic for certain of them, and it does indeed catch this one in addition to the previous ones. The upcoming 2.5-dev14 should be OK for you. Thank you very much for your useful report!