On Wed, Oct 04, 2023 at 22:19:32 +0100, Sergei Trofimovich via Gcc wrote: > The prototype that creates equivalent of the following commands does > work for smaller packages: > > > -fmacro-prefix-map=/nix/store/y8wfrgk7br5rfz4221lfb9v8w3n0cnyd-glibc-2.37-8-dev=/nix/store/eeeeeeeeeeeeeeeeeeeeeeeeeeeeeeee-glibc-2.37-8-dev > > -fmacro-prefix-map=/nix/store/8n240jfdmsb3lnc2qa2vb9dwk638j1lp-gmp-with-cxx-6.3.0-dev=/nix/store/eeeeeeeeeeeeeeeeeeeeeeeeeeeeeeee-gmp-with-cxx-6.3.0-dev > > -fmacro-prefix-map=/nix/store/phjcmy025rd1ankw5y1b21xsdii83cyk-nlohmann_json-3.11.2=/nix/store/eeeeeeeeeeeeeeeeeeeeeeeeeeeeeeee-nlohmann_json-3.11.2 > ... > > The above works for small amount of options (like, 100). But around 1000 > options we start hitting linux limits on the single environment variable > or real-world packages like `qemu` with a ton of input depends.
Are you trying to pass this through via `CFLAGS` and friends? > The command-line limitations are in various places: > - `gcc` limitation of lifting all command line options into a single > environment variable: https://gcc.gnu.org/PR111527 > - `linux` limitation of constraining single environ variable to a value > way below than full available environment space: > https://lkml.org/lkml/2023/9/24/381 > > `linux` fix would buy us 50x more budged (A Lot) but it will not help > much other operating systems like `Darwin` where absolute environment > limit is a lot lower than `linux`. > > I already implemented [1.] in https://github.com/NixOS/nixpkgs/pull/255192 > (also attached `mangle-NIX_STORE-in-__FILE__.patch` 3.5K patch against > `master` as a proof of concept). > > What would be the best way to scale up `-fmacro-prefix-map=` up to NixOS > needs for `gcc`? I would like to implement something sensible I could > upstream. How about `CFLAGS=@macro_prefix_map.args` and writing that file in the same codepath where you generate the flags today. It'll work with just about every compiler and tools like `ccache` will understand that it is an input that affects the build and properly take the file's contents into account. --Ben
