building 4.08.1 fails on fedora-32

[xaki23]

"found" while trying to build mirage-firewall.
seems like a gray area between "opam" and "ocaml", but @hannesm pointed me here.

switch create 4.08.1 fails on fedora-32 (gcc 10.0.1 and system-ocaml 4.10 )

# gcc -shared -o libcamlrun_shared.so interp_bpic.o misc_bpic.o stacks_bpic.o fix_code_bpic.o startup_aux_bpic.o startup_byt_bpic.o freelist_bpic.o major_gc_bpic.o minor_gc_bpic.o memory_bpic.o alloc_bpic.o roots_byt_bpic.o globroots_bpic.o fail_byt_bpic.o signals_bpic.o signals_byt_bpic.o printexc_bpic.o backtrace_byt_bpic.o backtrace_bpic.o compare_bpic.o ints_bpic.o floats_bpic.o str_bpic.o [...]
# /usr/bin/ld: backtrace_bpic.o:/home/user/.opam/mirage-firewall-4.08.1/.opam-switch/build/ocaml-base-compiler.4.08.1/runtime/backtrace.c:31: multiple definition of `caml_debug_info'; backtrace_byt_bpic.o:/home/user/.opam/mirage-firewall-4.08.1/.opam-switch/build/ocaml-base-compiler.4.08.1/runtime/backtrace_byt.c:47: first defined here
# collect2: error: ld returned 1 exit status
# make[1]: *** [Makefile:310: libcamlrun_shared.so] Error 1
# make[1]: Leaving directory '/home/user/.opam/mirage-firewall-4.08.1/.opam-switch/build/ocaml-base-compiler.4.08.1/runtime'
# make: *** [Makefile:323: coldstart] Error 2

[XVilka]

It's a problem of -fno-common with GCC 10, I suspect: https://gcc.gnu.org/gcc-10/porting_to.html

See the respective commit in OCaml 06db4c9

[xavierleroy]

The issue was fixed in OCaml 4.09.1 and 4.10.0. Could you use one of those versions instead of 4.08.1?

[xavierleroy]

Looks like the answer is "yes": mirage/qubes-mirage-firewall#96 (comment)

[psafont]

Are there any other workarounds for allowing 4.08.1 switches to be created using the latest version of gcc?

This is going to be painful for Citrix engineers as 4.08.1 is used in supported releases and it's meant to be supported for years.

[Octachron]

We are planning to publish updated opam packages for older OCaml versions with an explicit -fcommon flag.

See ocaml/opam-repository#16583 .

The easy path is to compile with CC="cc -fcommon". This has the unfortunate effect on turning off a de-optimization (-fno-tree-vrp) for gcc that is here as a workaround for an intel sky lake bug.

We willl publish the patched opam packages once this last wrinkle is figured out.

[glondu]

In Debian, I applied this patch, but the package FTBFS at the moment because of #9800 .