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	NixOS on RISC-V https://wiki.nixos.org/wiki/RISC-V https://pad.lassul.us/NixOS-riscv64-linux https://github.com/orgs/NixOS/teams/risc-v	64 Servers

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Sender	Message	Time
10 Apr 2026
cleverca22	`arch/riscv/include/asm/alternative-macros.h` reading more, i can see it will generate the first opcode, `nop`, and force it to not be compressed (so both options are 32bits) then it will use an assembly `.if` statement gated on the config flag, to maybe push the 2nd opcode into the `.alternative` section of the binary, along with some offsets to the `nop`	12:45:26
cleverca22	oh, but i also see things now gated by `CONFIG_RISCV_ALTERNATIVE`, hmmmm?	12:49:04
cleverca22	ah, when `CONFIG_RISCV_ALTERNATIVE=n` it just doesnt support the extensions at all, and always goes with the non-zbb case (in the strcmp example)	12:49:51
cleverca22	https://github.com/torvalds/linux/blob/master/arch/riscv/Kconfig#L542-L555	12:51:54
	@josw:matrix.org left the room.	16:46:54
13 Apr 2026
	Pol changed their display name from Slushee to Pol.	14:16:53
15 Apr 2026
	@98765abc:mozilla.org left the room.	06:49:36
	zoë (@blokyk) joined the room.	09:38:46
zoë (@blokyk)	i'm not sure if this is the right place to ask, especially because this is a very noob question, but i'm trying to get a shell for doing cross-compilation from x86 to riscv. I thought it'd be a simple matter of getting a `pkgsCross.riscv32.mkShell`/`stdenv` with the right `nativeBuildInputs` etc, but if i do `nix-shell -p pkgsCross.riscv32.stdenv`, I just get an x86->x86 toolchain instead of an x86->rv32 one... where's the problem with my mental model, and how can i get a shell with the right environment?	09:46:07
zoë (@blokyk)	i used this article and this one as sources, but I guess I might have missed or misunderstood something?	09:47:22
zoë (@blokyk)	* i used this article and this one as sources, but I guess I might h](https://www.hobson.space/posts/nixcross/)ave missed or misunderstood something?	09:47:47
zoë (@blokyk)	* i used this article and this one as sources, but I guess I might have missed or misunderstood something?	09:48:05
zoë (@blokyk)	* i used this article and this one as sources, but I guess I must have missed or misunderstood something?	09:48:14
zoë (@blokyk)	* i used this article and this one as sources, but I guess I must have missed or misunderstood something?	09:49:44
zoë (@blokyk)	* i'm not sure if this is the right place to ask, especially because this is a very noob question, but i'm trying to get a shell for doing cross-compilation from x86 to riscv. I thought it'd be a simple matter of getting a `pkgsCross.riscv32.mkShell`/`stdenv` with the right `nativeBuildInputs` etc, but if i do `nix-shell -p pkgsCross.riscv32.stdenv`, I just get an x86->x86 toolchain, and if i do `nix-shell -E '(import <nixpkgs> {}).pkgsCross.riscv32.mkShell {}` and try to compile a simple program, I get a `cc1: execvp: no such file or directory` error... where's the problem with my mental model, and how can i get a shell with the right environment?	09:54:19
zoë (@blokyk)	* i'm not sure if this is the right place to ask, especially because this is a very noob question, but i'm trying to get a shell for doing cross-compilation from x86 to riscv. I thought it'd be a simple matter of getting a `pkgsCross.riscv32.mkShell`/`stdenv` with the right `nativeBuildInputs` etc, but if i do `nix-shell -p pkgsCross.riscv32.stdenv`, I just get an x86->x86 toolchain, and if i do `nix-shell -E '(import <nixpkgs> {}).pkgsCross.riscv32.mkShell {}'` and try to compile a simple program, I get a `cc1: execvp: no such file or directory` error... where's the problem with my mental model, and how can i get a shell with the right environment?	09:59:49
zoë (@blokyk)	* i'm not sure if this is the right place to ask, especially because this is a very noob question, but i'm trying to get a shell for doing cross-compilation from x86 to riscv. I thought it'd be a simple matter of getting a `pkgsCross.riscv32.mkShell`/`stdenv` with the right `nativeBuildInputs` etc, but if i do `nix-shell -p pkgsCross.riscv32.stdenv`, I just get an x86->x86 toolchain (`which cc` points to a nix-managed gcc, but for x86)... where's the problem with my mental model, and how can i get a shell with the right environment?	10:01:19
zoë (@blokyk)	* i'm not sure if this is the right place to ask, especially because this is a very noob question, but i'm trying to get a shell for doing cross-compilation from x86 to riscv. I thought it'd be a simple matter of getting a `pkgsCross.riscv32.stdenv`/`mkShell` with the right `nativeBuildInputs` etc, but if i do `nix-shell -p pkgsCross.riscv32.stdenv`, I just get an x86->x86 toolchain (`which cc` points to a nix-managed gcc, but for x86)... where's the problem with my mental model, and how can i get a shell/derivation environment with the right toolchain?	10:12:44
zoë (@blokyk)	* i'm not sure if this is the right place to ask, especially because this is a very noob question, but i'm trying to get a shell for doing cross-compilation from x86 to riscv. I thought it'd be a simple matter of getting a `pkgsCross.riscv32.stdenv`/`mkShell` with the right `nativeBuildInputs` etc, but if i do `nix-shell -p pkgsCross.riscv32.stdenv`, I just get an x86->x86 toolchain (`which cc` points to a nix-managed gcc, but for x86)... where's the problem with my mental model, and how can i get a shell/derivation environment with the right toolchain? (ideally i'd also like to get an llvm-based toolchain, but that seems like it's basically completely unsupported)	10:14:20
zoë (@blokyk)	* i'm not sure if this is the right place to ask, especially because this is a very noob question, but i'm trying to get a shell for doing cross-compilation from x86 to riscv. I thought it'd be a simple matter of getting a `pkgsCross.riscv32.stdenv`/`mkShell` with the right `nativeBuildInputs` etc, but if i do `nix-shell -p pkgsCross.riscv32.stdenv`, I just get an x86->x86 toolchain (`which cc` points to a nix-managed gcc, but for x86)... where's the problem with my mental model, and how can i get a shell/derivation environment with the right toolchain? (ideally i'd also like to get an llvm-based toolchain, but that seems like it's basically completely unsupported ;-;)	10:14:27
zoë (@blokyk)	* i'm not sure if this is the right place to ask, especially because this is a very noob question, but i'm trying to get a shell for doing cross-compilation from x86 to riscv. I thought it'd be a simple matter of getting a `pkgsCross.riscv32.stdenv`/`mkShell` with the right `nativeBuildInputs` etc, but if i do `nix-shell -p pkgsCross.riscv32.stdenv`, I just get an x86->x86 toolchain (`which cc` points to a nix-managed gcc, but for x86)... where's the problem with my mental model, and how can i get a shell/derivation environment with the right toolchain? (ideally i'd also like to get an llvm-based toolchain, but that seems like it's basically completely unsupported ;-; i mean, `compiler-rt-libc-riscv32-unknown-linux-gnu` is broken so...)	10:15:21
zoë (@blokyk)	hmm, i might just be dumb... i though that `.stdenv` was basically just like an empty `mkDerivation { }` but I guess not also i got confused by `mkShell` having `which cc` point to my system's cc, but actually `$CC` is correct it seems. it's just going to be annoying since some of the stuff i want to use has `cc` in its makefiles instead of `$CC`	10:21:25
zoë (@blokyk)	Redacted or Malformed Event	10:50:43
zoë (@blokyk)	* ok so i wasn't going crazy: trying it out with just `nix-shell` and hard-coded `pkgsCross.riscv32.` in front of everything works, but for some reason `callPackage`/splicing doesn't work :( `# shell.nix { llvmPackages_latest, mkShell }: let mkLLVMShell = mkShell.override { inherit (llvmPackages_latest) stdenv; } in mkLLVMShell { }`	10:50:51
zoë (@blokyk)	* ok so i wasn't going crazy: trying it out with just `nix-shell` and hard-coded `pkgsCross.riscv32.` in front of everything works, but for some reason `callPackage`/splicing doesn't work :( `# shell.nix { llvmPackages_latest, mkShell }: let mkLLVMShell = mkShell.override { inherit (llvmPackages_latest) stdenv; } in mkLLVMShell { }` `$ nix-shell -E '(import <nixpkgs> {}).pkgsCross.riscv64.callPackage ./shell.nix {}' [nix-shell:~] $ $CC --version clang version 22.1.2 Target: x86_64-unknown-linux-gnu Thread model: posix InstalledDir: /nix/store/nqrpsik93243zfbysab689b4598x0srw-clang-22.1.2/bin` :(	10:53:55
zoë (@blokyk)	* ok so i wasn't going crazy: trying it out with just `nix-shell` and hard-coded `pkgsCross.riscv32.` in front of everything works, but for some reason `callPackage`/splicing doesn't work :( `# shell.nix { llvmPackages_latest, mkShell }: let mkLLVMShell = mkShell.override { inherit (llvmPackages_latest) stdenv; } in mkLLVMShell { }` `$ nix-shell -E '(import <nixpkgs> {}).pkgsCross.riscv64.callPackage ./shell.nix {}' [nix-shell:~]$ $CC --version clang version 22.1.2 Target: x86_64-unknown-linux-gnu Thread model: posix InstalledDir: /nix/store/nqrpsik93243zfbysab689b4598x0srw-clang-22.1.2/bin` :(	10:54:23
zoë (@blokyk)	* ok so i wasn't going crazy: trying it out with just `nix-shell` and hard-coded `pkgsCross.riscv32.` in front of everything works, but for some reason `callPackage`/splicing doesn't work :( `# shell.nix { llvmPackages_latest, mkShell }: let mkLLVMShell = mkShell.override { inherit (llvmPackages_latest) stdenv; }; in mkLLVMShell { }` `$ nix-shell -E '(import <nixpkgs> {}).pkgsCross.riscv64.callPackage ./shell.nix {}' [nix-shell:~]$ $CC --version clang version 22.1.2 Target: x86_64-unknown-linux-gnu Thread model: posix InstalledDir: /nix/store/nqrpsik93243zfbysab689b4598x0srw-clang-22.1.2/bin` :(	10:55:24
dramforever	`stdenv.cc` is the toolchain	13:01:19
dramforever	but otherwise yeah pkgsCross.riscv32.mkShell should get you what you want	13:03:23
zoë (@blokyk)	yeah idk what i did, i was just confused	13:03:49

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