Symptom: When building your app you see a bunch of errors like:
/usr/bin/ld: /home/you/.esy/3______________________________________________________________________/i/ocaml-4.9.1000-ffe51dac/lib/ocaml/libasmrun.a(roots_nat_n.o): relocation R_X86_64_32 against symbol `caml_frametable' can not be used when making a PIE object; recompile with -fPIE
/usr/bin/ld: /home/you/.esy/3______________________________________________________________________/i/ocaml-4.9.1000-ffe51dac/lib/ocaml/libasmrun.a(major_gc_n.o): relocation R_X86_64_32 against `.rodata.str1.1' can not be used when making a PIE object; recompile with -fPIE
/usr/bin/ld: /home/you/.esy/3______________________________________________________________________/i/ocaml-4.9.1000-ffe51dac/lib/ocaml/libasmrun.a(minor_gc_n.o): relocation R_X86_64_32 against `.rodata.str1.1' can not be used when making a PIE object; recompile with -fPIE
/usr/bin/ld: /home/you/.esy/3______________________________________________________________________/i/ocaml-4.9.1000-ffe51dac/lib/ocaml/libasmrun.a(memory_n.o): relocation R_X86_64_32 against symbol `caml_ref_table' can not be used when making a PIE object; recompile with -fPIE
Problem:
It is likely that your gcc is too old and it doesn't work well with the specific version of OCaml you are using.
What does which gcc pick up in your path? What is its version.
In your project what does ocaml -version report?
OCaml 4.9 has been known to have problems with really old gcc versions.
Likely Cause: Warming up your local build cache from CI when CI builds on a recent gcc, and your installed gcc is really old (With ubuntu this is common)
Solution:
Upgrade your ocaml in your package.json to 4.10.
If you did import CI artifacts, you may want to purge your ~/.esy/3_*/i directory.