Broken path rewrite in binary relocation for custom prefixes

[coffeejunk]

brew doctor output

Your system is ready to brew.

Verification

• I ran brew update twice and am still able to reproduce my issue.
• I have supplied my brew doctor output above and it seems unrelated to my issue.
• This issue's title and/or description do not reference a single formula e.g. brew install wget. If they do, open an issue at https://github.com/Homebrew/homebrew-core/issues/new/choose instead.
• I did not use AI/LLM to create this issue, or I disclosed the tool and model used; I will answer maintainer questions myself without AI/LLM.

brew config output

HOMEBREW_VERSION: 7.0.6
ORIGIN: https://github.com/Homebrew/brew
HEAD: 570982948a8a194f0f42f43f4a5bce2d1c9f64cb
Last commit: 26 hours ago
Branch: stable
Core tap: N/A
Core cask tap: N/A
HOMEBREW_PREFIX: /home/u/.b
HOMEBREW_REPOSITORY: /home/u/.b/Homebrew
HOMEBREW_CELLAR: /home/u/.b/Cellar
HOMEBREW_NO_ANALYTICS: set
HOMEBREW_NO_AUTO_UPDATE: set
HOMEBREW_NO_ENV_HINTS: set
Homebrew Ruby: 4.0.7 => /home/u/.b/Homebrew/Library/Homebrew/vendor/portable-ruby/4.0.7/bin/ruby
CPU: 16-core 64-bit zen4
Clang: N/A
Git: 2.55.0 => /bin/git
Curl: 8.15.0 => /bin/curl
Kernel: Linux 7.2.5-100.fc43.x86_64 x86_64 GNU/Linux
Landlock ABI: 10
OS: Fedora Linux 43 (Container Image)
Host glibc: 2.42
Host libstdc++: 6.0.34
/usr/bin/gcc: 15.3.1
/usr/bin/ruby: N/A
glibc: N/A
gcc@13: N/A
gcc: N/A
xorg: N/A

What were you trying to do (and why)?

What: Use Homebrew on Linux at a per-user prefix (/home/u/.b) instead of /home/linuxbrew/.linuxbrew.

Why: We are building a Linux-based immutable OS and rely on brew for the users' package management. To better support multi-user situations, we install brew per user in ~/.b.

What happened (include all command output)?

I ran into this issue when installing fonts and fontconfig:

$ ~/.b/bin/fc-match sans-serif
Fontconfig error: Cannot load default config file: File not found
DejaVuSans.ttf: "DejaVu Sans" "Book"

$ strace -e trace=access -P /home/linuxbrew/.linuxbrew/etc/fonts/fonts.conf ~/.b/bin/fc-match sans-serif
access("/home/linuxbrew/.linuxbrew/etc/fonts/fonts.conf", R_OK) = -1 ENOENT (No such file or directory)

When Homebrew is installed at a prefix other than /home/linuxbrew/.linuxbrew, it rewrites the build prefix in
the installed files. The rewrite currently only finds the prefix where it is stored as one string. Compiled code sometimes
holds a path in 8-byte pieces spread over several instructions instead, which the rewrite doesn't touch:

$ ruby split-prefix.rb ~/.b/Cellar
avahi/0.9-rc5/sbin/avahi-daemon: /home/li|nuxbrew/|.linuxbr|ew/var/r|un/avahi|-daemon/|socket
avahi/0.9-rc5/sbin/avahi-dnsconfd: /home/li|nuxbrew/|.linuxbr|ew/var/r|un/avahi|-daemon/|socket
fontconfig/2.18.3/lib/libfontconfig.so.1.17.0: /home/li|nuxbrew/|.linuxbr|ew/etc/f|c/fonts
glib/2.90.0/lib/libgio-2.0.so.0.9000.0: /home/li|nuxbrew/|.linuxbr|ew/lib/g|io/modul
glib/2.90.0/lib/libgirepository-2.0.so.0.9000.0: /home/li|nuxbrew/|.linuxbr|ew/lib/g|ireposit|ory-1.0
glib/2.90.0/lib/libglib-2.0.so.0.9000.0: /home/li|nuxbrew/|.linuxbr|ew/Cella|r/glib/2|.90.0/li|charset.|t.alias
gtk+3/3.24.52/lib/libgtk-3.so.0.2420.32: /home/li|nuxbrew/|.linuxbr|ew/Cella|r/gtk+3/|3.24.52/|2/share
gtk+3/3.24.52/lib/libgtk-3.so.0.2420.32: /home/li|nuxbrew/|.linuxbr|ew/Cella|r/libx11|/1.8.13/|share/X1|1/locale
util-linux/2.42.3/lib/libuuid.so.1.3.0: /home/li|nuxbrew/|.linuxbr|ew/Cella|r/util-l|inux/2.4|2.3/var/|run/uuid|d/reques

Script listing paths stored in 8-byte pieces inside machine code `split-prefix.rb`

#!/usr/bin/env ruby
# List ELF files under a directory in which the Homebrew build prefix is
# written 8 bytes at a time by x86-64 `movabs` instructions instead of being
# stored as one string. Prints the file and the pieces the immediates hold.
require "find"

PREFIX = "/home/linuxbrew/.linuxbrew".b
MOVABS = /\x48[\xb8-\xbf](.{8})/mn
CHAIN_START = /\x48[\xb8-\xbf]#{Regexp.escape(PREFIX[0, 8])}/mn

root = ARGV.fetch(0)
Find.find(root) do |path|
  next if File.symlink?(path) || !File.file?(path)

  data = File.binread(path)
  next unless data.start_with?("\x7fELF".b)

  data.to_enum(:scan, CHAIN_START).map { Regexp.last_match.begin(0) }.each do |start|
    pieces = []
    pos = start
    while (m = MOVABS.match(data, pos)) && m.begin(0) < pos + 40
      pieces << m[1]
      pos = m.end(0)
    end
    next unless pieces.join.start_with?(PREFIX)

    puts "#{path.delete_prefix("#{root}/")}: #{pieces.join("|")}"
  end
end

What did you expect to happen?

fc-match reads /home/u/.b/etc/fonts/fonts.conf and prints no error, as it does with FONTCONFIG_PATH=~/.b/etc/fonts set:

$ FONTCONFIG_PATH=~/.b/etc/fonts ~/.b/bin/fc-match sans-serif
DejaVuSans.ttf: "DejaVu Sans" "Book"

Step-by-step reproduction instructions (running brew commands)

NONINTERACTIVE=1 bash -c "$(curl -fsSL https://raw.githubusercontent.com/Homebrew/install/HEAD/install.sh)" -- --path="$HOME/.b"
export PATH="$HOME/.b/bin:$PATH"
brew install fontconfig
fc-match sans-serif


Full repro in containers:


*Ubuntu 24.04*


podman run --rm ubuntu:24.04 bash -c "$(cat <<'EOF'
set -e
apt-get update -qq >/dev/null
apt-get install -y -qq build-essential procps curl file git strace >/dev/null 2>&1
useradd -m u
su - u -s /bin/bash <<'USER'
export PATH=$HOME/.b/bin:$PATH HOMEBREW_NO_AUTO_UPDATE=1 HOMEBREW_NO_ANALYTICS=1 HOMEBREW_NO_ENV_HINTS=1
NONINTERACTIVE=1 bash -c "$(curl -fsSL https://raw.githubusercontent.com/Homebrew/install/HEAD/install.sh)" -- --path="$HOME/.b" >/dev/null 2>&1
set -x
brew update </dev/null
brew update </dev/null
brew install fontconfig </dev/null 2>&1 | grep Pouring.fontconfig
brew doctor
ls -l ~/.b/etc/fonts/fonts.conf
fc-match sans-serif
strace -e trace=access -P /home/linuxbrew/.linuxbrew/etc/fonts/fonts.conf fc-match sans-serif
FONTCONFIG_PATH=~/.b/etc/fonts fc-match sans-serif
USER
EOF
)"


Output:


+ brew update
==> Updating Homebrew...
Already up-to-date.
+ brew update
==> Updating Homebrew...
Already up-to-date.
+ brew install fontconfig
+ grep Pouring.fontconfig
==> Pouring fontconfig--2.18.3.x86_64_linux.bottle.tar.gz
+ brew doctor
Your system is ready to brew.
+ ls -l /home/u/.b/etc/fonts/fonts.conf
-rw-r--r--. 1 u u 2710 Sep 22 18:08 /home/u/.b/etc/fonts/fonts.conf
+ fc-match sans-serif
Fontconfig error: Cannot load default config file: File not found
DejaVuSans.ttf: "DejaVu Sans" "Book"
+ strace -e trace=access -P /home/linuxbrew/.linuxbrew/etc/fonts/fonts.conf fc-match sans-serif
access("/home/linuxbrew/.linuxbrew/etc/fonts/fonts.conf", R_OK) = -1 ENOENT (No such file or directory)
Fontconfig error: Cannot load default config file: File not found
DejaVuSans.ttf: "DejaVu Sans" "Book"
+++ exited with 0 +++
+ FONTCONFIG_PATH=/home/u/.b/etc/fonts
+ fc-match sans-serif
DejaVuSans.ttf: "DejaVu Sans" "Book"


*Fedora 43*


podman run --rm fedora:43 bash -c "$(cat <<'EOF'
set -e
dnf install -y -q gcc gcc-c++ make procps-ng curl file git strace dejavu-sans-fonts >/dev/null 2>&1
useradd -m u
su - u -s /bin/bash <<'USER'
export PATH=$HOME/.b/bin:$PATH HOMEBREW_NO_AUTO_UPDATE=1 HOMEBREW_NO_ANALYTICS=1 HOMEBREW_NO_ENV_HINTS=1
NONINTERACTIVE=1 bash -c "$(curl -fsSL https://raw.githubusercontent.com/Homebrew/install/HEAD/install.sh)" -- --path="$HOME/.b" >/dev/null 2>&1
set -x
brew update </dev/null
brew update </dev/null
brew install fontconfig </dev/null 2>&1 | grep Pouring.fontconfig
brew doctor
ls -l ~/.b/etc/fonts/fonts.conf
fc-match sans-serif
strace -e trace=access -P /home/linuxbrew/.linuxbrew/etc/fonts/fonts.conf fc-match sans-serif
FONTCONFIG_PATH=~/.b/etc/fonts fc-match sans-serif
USER
EOF
)"


Output:


+ brew update
==> Updating Homebrew...
Already up-to-date.
+ brew update
==> Updating Homebrew...
Already up-to-date.
+ brew install fontconfig
+ grep Pouring.fontconfig
==> Pouring fontconfig--2.18.3.x86_64_linux.bottle.tar.gz
+ brew doctor
Your system is ready to brew.
+ ls -l /home/u/.b/etc/fonts/fonts.conf
-rw-r--r--. 1 u u 2710 Sep 22 18:09 /home/u/.b/etc/fonts/fonts.conf
+ fc-match sans-serif
Fontconfig error: Cannot load default config file: File not found
DejaVuSans.ttf: "DejaVu Sans" "Book"
+ strace -e trace=access -P /home/linuxbrew/.linuxbrew/etc/fonts/fonts.conf fc-match sans-serif
access("/home/linuxbrew/.linuxbrew/etc/fonts/fonts.conf", R_OK) = -1 ENOENT (No such file or directory)
Fontconfig error: Cannot load default config file: File not found
DejaVuSans.ttf: "DejaVu Sans" "Book"
+++ exited with 0 +++
+ FONTCONFIG_PATH=/home/u/.b/etc/fonts
+ fc-match sans-serif
DejaVuSans.ttf: "DejaVu Sans" "Book"


Debugged with the help of Claude Code (Fable 5.1)

[Puma1235]

/bin/bash -c "$(curl -fsSL https://raw.githubusercontent.com/Homebrew/install/HEAD/install.sh)"

[Puma1235]

``/bin/bash -c "$(curl -fsSL https://raw.githubusercontent.com/Homebrew/install/HEAD/install.sh)"