From 8ad63194e7e8e1cdd4c29155c342499d7815e14f Mon Sep 17 00:00:00 2001
From: Sergio Lopez <slp@redhat.com>
Date: Thu, 18 Sep 2025 15:13:10 +0200
Subject: [PATCH] Re-execute itself with DYLD_LIBRARY_PATH

After libkrun stopped linking directly against libkrunfw, we depend on
dlopen() and the system's linker to do a sane job at looking for the
library. This poses a problem on macOS, since the library path from
the brew prefix is not used for looking up libraries by default.

So work around this limitation, look if the DYLD_LIBRARY_PATH
environment variable is present. If it isn't, obtain the brew prefix and
re-execute krunvm with pushing that variable with brew's library path
into the list of environment variables.

Fixes: #70
Signed-off-by: Sergio Lopez <slp@redhat.com>
---
 Cargo.toml  |  2 +-
 src/main.rs | 61 ++++++++++++++++++++++++++++++++++++++++++++++++++++-
 2 files changed, 61 insertions(+), 2 deletions(-)

diff --git a/Cargo.toml b/Cargo.toml
index 1462c47..80f19a2 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -15,4 +15,4 @@ libc = "0.2.82"
 serde = "1.0.120"
 serde_derive = "1.0.120"
 text_io = "0.1.8"
-nix = {version = "0.27.1", features = ["socket", "fs"]}
+nix = {version = "0.27.1", features = ["socket", "fs", "process"]}
diff --git a/src/main.rs b/src/main.rs
index 3be6e5a..d6f336d 100644
--- a/src/main.rs
+++ b/src/main.rs
@@ -2,15 +2,19 @@
 // SPDX-License-Identifier: Apache-2.0
 
 use std::collections::HashMap;
+use std::env;
+use std::ffi::CString;
 #[cfg(target_os = "macos")]
 use std::fs::File;
 #[cfg(target_os = "macos")]
-use std::io::{self, Read, Write};
+use std::io::{self, Error, ErrorKind, Read, Write};
+use std::os::unix::ffi::OsStringExt;
 
 use crate::commands::{
     ChangeVmCmd, ConfigCmd, CreateCmd, DeleteCmd, InspectCmd, ListCmd, StartCmd,
 };
 use clap::{Parser, Subcommand};
+use nix::unistd::execve;
 use serde_derive::{Deserialize, Serialize};
 #[cfg(target_os = "macos")]
 use text_io::read;
@@ -169,7 +173,62 @@ enum Command {
     Config(ConfigCmd),
 }
 
+#[cfg(target_os = "macos")]
+fn get_brew_prefix() -> Option<String> {
+    let output = std::process::Command::new("brew")
+        .arg("--prefix")
+        .stderr(std::process::Stdio::inherit())
+        .output()
+        .ok()?;
+
+    let exit_code = output.status.code().unwrap_or(-1);
+    if exit_code != 0 {
+        return None;
+    }
+
+    Some(std::str::from_utf8(&output.stdout).ok()?.trim().to_string())
+}
+
+#[cfg(target_os = "macos")]
+fn reexec() -> Result<(), Error> {
+    let args: Vec<CString> = env::args_os()
+        .map(|arg| CString::new(arg.into_vec()).unwrap())
+        .collect();
+
+    let mut envs: Vec<CString> = env::vars_os()
+        .map(|(key, value)| {
+            CString::new(format!(
+                "{}={}",
+                key.into_string().unwrap(),
+                value.into_string().unwrap()
+            ))
+            .unwrap()
+        })
+        .collect();
+    let brew_prefix = get_brew_prefix().ok_or(ErrorKind::NotFound)?;
+    envs.push(CString::new(format!(
+        "DYLD_LIBRARY_PATH={brew_prefix}/lib"
+    ))?);
+
+    // Use execve to replace the current process. This function only returns
+    // if an error occurs.
+    match execve(&args[0], &args, &envs) {
+        Ok(_) => Ok(()),
+        Err(e) => {
+            eprintln!("Error re-executing krunvm: {}", e);
+            std::process::exit(-1);
+        }
+    }
+}
+
 fn main() {
+    #[cfg(target_os = "macos")]
+    {
+        if env::var("DYLD_LIBRARY_PATH").is_err() {
+            _ = reexec();
+        }
+    }
+
     let mut cfg: KrunvmConfig = confy::load(APP_NAME).unwrap();
     let cli_args = Cli::parse();