fix compilation with new new nightly VaList

In 2025-12-05, a Rust pull request at
rust-lang/rust#141980
reworked the `VaList` implementation to be abi-compatible with C. This
broke:

  * the `printf-compat` implementation, which is fixed in version 0.3
  * pretty much every function that methods of `VaList` (most commonly
    `as_va_list`), since they no longer exist

Here, we fix both of those problems and update the compiler version in
`rust-toolchain.toml` to be the oldest compiler that will already have
this new implementation.

Updating the compiler has created 2 unforseen problems:

  1. When unwinding, the new Rust version now prints the process's PID.
     This means for the `c-gull-unwinding` we can no longer use the
     `assert_cmd` API, as it does not expose the child PID to us.
  2. The `c-gull/src/nss.rs` had 3 extra warnings of operations whose
     results were unused. This was also breaking some other tests.

Both of these were also fixed.

Author: LGFae

c-gull/src/nss.rs

@@ -305,10 +305,8 @@ unsafe fn getgr_r(
     };
     let pad = align_of::<*const c_char>() - (buf.addr()) % align_of::<*const c_char>();
     buf = buf.add(pad);
-    buflen -= pad;
     let gr_mem = buf.cast::<*mut c_char>();
     buf = gr_mem.add(num_members + 1).cast::<c_char>();
-    buflen -= buf.addr() - gr_mem.addr();
 
     let mut cur_mem = gr_mem;
     if num_members != 0 {
@@ -319,7 +317,6 @@ unsafe fn getgr_r(
             buf = buf.add(member.len());
             write(buf, 0);
             buf = buf.add(1);
-            buflen -= member.len() + 1;
         }
     }
     write(cur_mem, null_mut());

c-scape/Cargo.toml

@@ -34,7 +34,7 @@ rand = { version = "0.9.0", default-features = false }
 rustix-dlmalloc = { version = "0.2.1", optional = true }
 rustix-openpty = "0.2.0"
 bitflags = { version = "2.4.1", default-features = false }
-printf-compat = { version = "0.2.1", default-features = false }
+printf-compat = { version = "0.3.0", default-features = false }
 num-complex = { version = "0.4.4", default-features = false, features = ["libm"] }
 posix-regex = { version = "0.1.1", features = ["no_std"] }
 

c-scape/src/fs/fcntl.rs

@@ -9,18 +9,16 @@ use libc::c_int;
 use crate::convert_res;
 
 #[no_mangle]
-unsafe extern "C" fn fcntl(fd: c_int, cmd: c_int, mut args: ...) -> c_int {
-    let args = args.as_va_list();
+unsafe extern "C" fn fcntl(fd: c_int, cmd: c_int, args: ...) -> c_int {
     _fcntl::<libc::flock>(fd, cmd, args)
 }
 
 #[no_mangle]
-unsafe extern "C" fn fcntl64(fd: c_int, cmd: c_int, mut args: ...) -> c_int {
-    let args = args.as_va_list();
+unsafe extern "C" fn fcntl64(fd: c_int, cmd: c_int, args: ...) -> c_int {
     _fcntl::<libc::flock64>(fd, cmd, args)
 }
 
-unsafe fn _fcntl<FlockTy: Flock>(fd: c_int, cmd: c_int, mut args: VaList<'_, '_>) -> c_int {
+unsafe fn _fcntl<FlockTy: Flock>(fd: c_int, cmd: c_int, mut args: VaList<'_>) -> c_int {
     match cmd {
         libc::F_GETFL => {
             libc!(libc::fcntl(fd, libc::F_GETFL));

c-scape/src/stdio.rs

@@ -714,30 +714,24 @@ unsafe fn parse_oflags(mode: *const c_char) -> Option<OFlags> {
 }
 
 #[no_mangle]
-unsafe extern "C" fn printf(fmt: *const c_char, mut args: ...) -> c_int {
-    let va_list = args.as_va_list();
-    vprintf(fmt, va_list)
+unsafe extern "C" fn printf(fmt: *const c_char, args: ...) -> c_int {
+    vprintf(fmt, args)
 }
 
 #[no_mangle]
-unsafe extern "C" fn vprintf(fmt: *const c_char, va_list: VaList<'_, '_>) -> c_int {
+unsafe extern "C" fn vprintf(fmt: *const c_char, va_list: VaList<'_>) -> c_int {
     //libc!(libc::vprintf(fmt, va_list));
 
     vfprintf(stdout, fmt, va_list)
 }
 
 #[no_mangle]
-unsafe extern "C" fn sprintf(ptr: *mut c_char, fmt: *const c_char, mut args: ...) -> c_int {
-    let va_list = args.as_va_list();
-    vsprintf(ptr, fmt, va_list)
+unsafe extern "C" fn sprintf(ptr: *mut c_char, fmt: *const c_char, args: ...) -> c_int {
+    vsprintf(ptr, fmt, args)
 }
 
 #[no_mangle]
-unsafe extern "C" fn vsprintf(
-    ptr: *mut c_char,
-    fmt: *const c_char,
-    va_list: VaList<'_, '_>,
-) -> c_int {
+unsafe extern "C" fn vsprintf(ptr: *mut c_char, fmt: *const c_char, va_list: VaList<'_>) -> c_int {
     //libc!(libc::vsprintf(ptr, fmt, va_list));
 
     let mut out = String::new();
@@ -762,18 +756,17 @@ unsafe extern "C" fn snprintf(
     ptr: *mut c_char,
     len: usize,
     fmt: *const c_char,
-    mut args: ...
+    args: ...
 ) -> c_int {
-    let va_list = args.as_va_list();
-    vsnprintf(ptr, len, fmt, va_list)
+    vsnprintf(ptr, len, fmt, args)
 }
 
 #[no_mangle]
 unsafe extern "C" fn vsnprintf(
     ptr: *mut c_char,
     len: usize,
     fmt: *const c_char,
-    va_list: VaList<'_, '_>,
+    va_list: VaList<'_>,
 ) -> c_int {
     //libc!(libc::vsnprintf(ptr, len, fmt, va_list));
 
@@ -797,13 +790,12 @@ unsafe extern "C" fn vsnprintf(
 }
 
 #[no_mangle]
-unsafe extern "C" fn dprintf(fd: c_int, fmt: *const c_char, mut args: ...) -> c_int {
-    let va_list = args.as_va_list();
-    vdprintf(fd, fmt, va_list)
+unsafe extern "C" fn dprintf(fd: c_int, fmt: *const c_char, args: ...) -> c_int {
+    vdprintf(fd, fmt, args)
 }
 
 #[no_mangle]
-unsafe extern "C" fn vdprintf(fd: c_int, fmt: *const c_char, va_list: VaList<'_, '_>) -> c_int {
+unsafe extern "C" fn vdprintf(fd: c_int, fmt: *const c_char, va_list: VaList<'_>) -> c_int {
     //libc!(libc::vdprintf(fd, fmt, va_list));
 
     let mut out = String::new();
@@ -830,16 +822,15 @@ unsafe extern "C" fn vdprintf(fd: c_int, fmt: *const c_char, va_list: VaList<'_,
 }
 
 #[no_mangle]
-unsafe extern "C" fn fprintf(file: *mut libc::FILE, fmt: *const c_char, mut args: ...) -> c_int {
-    let va_list = args.as_va_list();
-    vfprintf(file, fmt, va_list)
+unsafe extern "C" fn fprintf(file: *mut libc::FILE, fmt: *const c_char, args: ...) -> c_int {
+    vfprintf(file, fmt, args)
 }
 
 #[no_mangle]
 unsafe extern "C" fn vfprintf(
     file: *mut libc::FILE,
     fmt: *const c_char,
-    va_list: VaList<'_, '_>,
+    va_list: VaList<'_>,
 ) -> c_int {
     //libc!(libc::vfprintf(file, fmt, va_list));
 
@@ -858,9 +849,9 @@ unsafe extern "C" fn vfprintf(
 unsafe extern "C" fn vasprintf(
     strp: *mut *mut c_char,
     fmt: *const c_char,
-    va_list: VaList<'_, '_>,
+    va_list: VaList<'_>,
 ) -> c_int {
-    let len = va_list.with_copy(|va_list| vsnprintf(null_mut(), 0, fmt, va_list));
+    let len = vsnprintf(null_mut(), 0, fmt, va_list.clone());
     if len < 0 {
         return -1;
     }
@@ -875,9 +866,8 @@ unsafe extern "C" fn vasprintf(
 }
 
 #[no_mangle]
-unsafe extern "C" fn asprintf(strp: *mut *mut c_char, fmt: *const c_char, mut args: ...) -> c_int {
-    let va_list = args.as_va_list();
-    vasprintf(strp, fmt, va_list)
+unsafe extern "C" fn asprintf(strp: *mut *mut c_char, fmt: *const c_char, args: ...) -> c_int {
+    vasprintf(strp, fmt, args)
 }
 
 #[no_mangle]

c-scape/src/stdio/chk.rs

@@ -17,10 +17,9 @@ unsafe extern "C" fn __snprintf_chk(
     flag: c_int,
     slen: size_t,
     fmt: *const c_char,
-    mut args: ...
+    args: ...
 ) -> c_int {
-    let va_list = args.as_va_list();
-    __vsnprintf_chk(ptr, len, flag, slen, fmt, va_list)
+    __vsnprintf_chk(ptr, len, flag, slen, fmt, args)
 }
 
 // <https://refspecs.linuxbase.org/LSB_5.0.0/LSB-Core-generic/LSB-Core-generic/baselib---vsnprintf-chk-1.html>
@@ -31,7 +30,7 @@ unsafe extern "C" fn __vsnprintf_chk(
     flag: c_int,
     slen: size_t,
     fmt: *const c_char,
-    va_list: VaList<'_, '_>,
+    va_list: VaList<'_>,
 ) -> c_int {
     if slen < len {
         __chk_fail();
@@ -51,10 +50,9 @@ unsafe extern "C" fn __sprintf_chk(
     flag: c_int,
     strlen: size_t,
     format: *const c_char,
-    mut args: ...
+    args: ...
 ) -> c_int {
-    let va_list = args.as_va_list();
-    __vsprintf_chk(ptr, flag, strlen, format, va_list)
+    __vsprintf_chk(ptr, flag, strlen, format, args)
 }
 
 #[no_mangle]
@@ -63,7 +61,7 @@ unsafe extern "C" fn __vsprintf_chk(
     flag: c_int,
     strlen: size_t,
     fmt: *const c_char,
-    va_list: VaList<'_, '_>,
+    va_list: VaList<'_>,
 ) -> c_int {
     if flag > 0 {
         unimplemented!("__USE_FORTIFY_LEVEL > 0");
@@ -88,10 +86,9 @@ unsafe extern "C" fn __fprintf_chk(
     file: *mut libc::FILE,
     flag: c_int,
     fmt: *const c_char,
-    mut args: ...
+    args: ...
 ) -> c_int {
-    let va_list = args.as_va_list();
-    __vfprintf_chk(file, flag, fmt, va_list)
+    __vfprintf_chk(file, flag, fmt, args)
 }
 
 // <https://refspecs.linuxbase.org/LSB_5.0.0/LSB-Core-generic/LSB-Core-generic/baselib---vfprintf-chk-1.html>
@@ -100,7 +97,7 @@ unsafe extern "C" fn __vfprintf_chk(
     file: *mut libc::FILE,
     flag: c_int,
     fmt: *const c_char,
-    va_list: VaList<'_, '_>,
+    va_list: VaList<'_>,
 ) -> c_int {
     if flag > 0 {
         unimplemented!("__USE_FORTIFY_LEVEL > 0");
@@ -113,17 +110,12 @@ unsafe extern "C" fn __vfprintf_chk(
 
 // <https://refspecs.linuxbase.org/LSB_5.0.0/LSB-Core-generic/LSB-Core-generic/baselib---printf-chk-1.html>
 #[no_mangle]
-unsafe extern "C" fn __printf_chk(flag: c_int, fmt: *const c_char, mut args: ...) -> c_int {
-    let va_list = args.as_va_list();
-    __vprintf_chk(flag, fmt, va_list)
+unsafe extern "C" fn __printf_chk(flag: c_int, fmt: *const c_char, args: ...) -> c_int {
+    __vprintf_chk(flag, fmt, args)
 }
 
 #[no_mangle]
-unsafe extern "C" fn __vprintf_chk(
-    flag: c_int,
-    fmt: *const c_char,
-    va_list: VaList<'_, '_>,
-) -> c_int {
+unsafe extern "C" fn __vprintf_chk(flag: c_int, fmt: *const c_char, va_list: VaList<'_>) -> c_int {
     if flag > 0 {
         unimplemented!("__USE_FORTIFY_LEVEL > 0");
     }
@@ -138,18 +130,17 @@ unsafe extern "C" fn __asprintf_chk(
     strp: *mut *mut c_char,
     flag: c_int,
     fmt: *const c_char,
-    mut args: ...
+    args: ...
 ) -> c_int {
-    let va_list = args.as_va_list();
-    __vasprintf_chk(strp, flag, fmt, va_list)
+    __vasprintf_chk(strp, flag, fmt, args)
 }
 
 #[no_mangle]
 unsafe extern "C" fn __vasprintf_chk(
     strp: *mut *mut c_char,
     flag: c_int,
     fmt: *const c_char,
-    va_list: VaList<'_, '_>,
+    va_list: VaList<'_>,
 ) -> c_int {
     if flag > 0 {
         unimplemented!("__USE_FORTIFY_LEVEL > 0");
@@ -159,22 +150,16 @@ unsafe extern "C" fn __vasprintf_chk(
 }
 
 #[no_mangle]
-unsafe extern "C" fn __dprintf_chk(
-    fd: c_int,
-    flag: c_int,
-    fmt: *const c_char,
-    mut args: ...
-) -> c_int {
-    let va_list = args.as_va_list();
-    __vdprintf_chk(fd, flag, fmt, va_list)
+unsafe extern "C" fn __dprintf_chk(fd: c_int, flag: c_int, fmt: *const c_char, args: ...) -> c_int {
+    __vdprintf_chk(fd, flag, fmt, args)
 }
 
 #[no_mangle]
 unsafe extern "C" fn __vdprintf_chk(
     fd: c_int,
     flag: c_int,
     fmt: *const c_char,
-    va_list: VaList<'_, '_>,
+    va_list: VaList<'_>,
 ) -> c_int {
     if flag > 0 {
         unimplemented!("__USE_FORTIFY_LEVEL > 0");

rust-toolchain.toml

@@ -1,3 +1,3 @@
 [toolchain]
-channel = "nightly-2025-04-28"
+channel = "nightly-2025-12-07"
 components = ["rustc", "cargo", "rust-std", "rust-src", "rustfmt"]

tests/example_crates.rs

@@ -140,14 +140,57 @@ fn example_crate_c_scape_unwinding() {
 
 #[test]
 fn example_crate_c_gull_unwinding() {
-    test_crate(
-        "c-gull-unwinding",
-        &[],
-        &[("RUST_BACKTRACE", "0")],
-        "Hello, world!\nHello world using libc `printf`!\n",
-        "\nthread 'main' panicked at src/main.rs:18:5:\ncatch me!\nnote: run with `RUST_BACKTRACE=1` environment variable to display a backtrace\n",
-        None,
+    // Note: Rust's default unwind now prints a message with the process's PID. The assert_cmd
+    // command does not let us get the child's PID. So we have to use the std::process::Command API
+    // instead.
+    use std::process::Command;
+    use std::process::Stdio;
+
+    #[cfg(target_arch = "x86_64")]
+    let arch = "x86_64";
+    #[cfg(target_arch = "aarch64")]
+    let arch = "aarch64";
+    #[cfg(target_arch = "riscv64")]
+    let arch = "riscv64gc";
+    #[cfg(target_arch = "x86")]
+    let arch = "i686";
+    #[cfg(target_arch = "arm")]
+    let arch = "armv5te";
+    #[cfg(target_env = "gnueabi")]
+    let env = "gnueabi";
+    #[cfg(all(target_env = "gnu", target_abi = "eabi"))]
+    let env = "gnueabi";
+    #[cfg(all(target_env = "gnu", not(target_abi = "eabi")))]
+    let env = "gnu";
+
+    let mut command = Command::new("cargo");
+    command.arg("run").arg("--quiet");
+    command.arg(&format!("--target={}-unknown-linux-{}", arch, env));
+
+    command.env("RUST_BACKTRACE", "0");
+    command.current_dir("example-crates/c-gull-unwinding");
+
+    command.stdout(Stdio::piped());
+    command.stderr(Stdio::piped());
+
+    let child = command.spawn().unwrap();
+    let pid = child.id();
+    let output = child.wait_with_output().unwrap();
+
+    assert_eq!(
+        std::str::from_utf8(&output.stdout).unwrap(),
+        "Hello, world!\nHello world using libc `printf`!\n"
+    );
+    assert_eq!(
+        std::str::from_utf8(&output.stderr).unwrap(),
+        format!(
+            "\nthread 'main' ({pid}) panicked at src/main.rs:18:5:\n\
+            catch me!\n\
+            note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace\n"
+        )
+        .as_str()
     );
+    assert!(output.status.success());
 }
 
 #[test]