fix(FreeBSD): remove null terminator from executable path #14618
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On FreeBSD, sysctl(KERN_PROC_PATHNAME) returns a null-terminated
string with pathLen including the terminator. This causes Nix to
fail during manual generation with:
error:
… while calling the 'concatStringsSep' builtin
at /nix/var/nix/builds/nix-63232-402489527/source/doc/manual/generate-settings.nix:99:1:
98| in
99| concatStrings (attrValues (mapAttrs (showSetting prefix) settingsInfo))
| ^
100|
error: input string '/nix/store/gq89cj02b5zs67cbd85vzg5cgsgnd8mj-nix-2.31.2/bin/nix␀'
cannot be represented as Nix string because it contains null bytes
The issue occurs because generate-settings.nix reads the nix binary
path from JSON and evaluates it as a Nix string, which cannot contain
null bytes. Normal C++ string operations don't trigger this since they
handle null-terminated strings correctly.
Strip the null terminator on FreeBSD to match other platforms (Linux
uses /proc/self/exe, macOS uses _NSGetExecutablePath).
Credit: @wahjava (FreeBSD ports and Nixpkgs contributor)
xokdvium
approved these changes
Nov 22, 2025
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Motivation
On FreeBSD, sysctl(KERN_PROC_PATHNAME) returns a null-terminated string with pathLen including the terminator. This causes Nix to fail during manual generation with:
The issue occurs because generate-settings.nix reads the nix binary path from JSON and evaluates it as a Nix string, which cannot contain null bytes. Normal C++ string operations don't trigger this since they handle null-terminated strings correctly.
Strip the null terminator on FreeBSD to match other platforms (Linux uses /proc/self/exe, macOS uses _NSGetExecutablePath).
Credit: @wahjava (FreeBSD ports and Nixpkgs contributor)
Context
Building Nix using Nix on FreeBSD (testing native compilation of NixBSD)
This patch comes from freebsd-ports, I tried to improve the explanation and rationale in the comment and commit message. It's helpful to have this change upstream so that it does not need to be patched in manually, and it is relevant for NixBSD.
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