[PATCH 11/33] rust: remove unused global qemu "allocator"

[Paolo Bonzini <pbonzini@redhat.com>]

From: Marc-André Lureau <marcandre.lureau@redhat.com>

The global allocator has always been disabled. There is no clear reason
Rust and C should use the same allocator. Allocations made from Rust
must be freed by Rust, and same for C, otherwise we head into troubles.

Signed-off-by: Marc-André Lureau <marcandre.lureau@redhat.com>
Link: https://lore.kernel.org/r/20250827104147.717203-3-marcandre.lureau@redhat.com
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
---
 meson.build               |   4 --
 rust/Cargo.toml           |   2 +-
 rust/qemu-api/Cargo.toml  |   1 -
 rust/qemu-api/meson.build |   1 -
 rust/qemu-api/src/lib.rs  | 135 --------------------------------------
 5 files changed, 1 insertion(+), 142 deletions(-)

diff --git a/meson.build b/meson.build
index ef3f52b951d..49395197f44 100644
--- a/meson.build
+++ b/meson.build
@@ -1090,9 +1090,6 @@ glib = declare_dependency(dependencies: [glib_pc, gmodule],
 # TODO: remove this check and the corresponding workaround (qtree) when
 # the minimum supported glib is >= 2.75.3
 glib_has_gslice = glib.version().version_compare('<2.75.3')
-# Check whether glib has the aligned_alloc family of functions.
-# <https://docs.gtk.org/glib/func.aligned_alloc.html>
-glib_has_aligned_alloc = glib.version().version_compare('>=2.72.0')
 
 # override glib dep to include the above refinements
 meson.override_dependency('glib-2.0', glib)
@@ -2706,7 +2703,6 @@ config_host_data.set('CONFIG_GETLOADAVG', cc.has_function('getloadavg'))
 config_host_data.set('HAVE_COPY_FILE_RANGE', cc.has_function('copy_file_range'))
 config_host_data.set('HAVE_GETIFADDRS', cc.has_function('getifaddrs'))
 config_host_data.set('HAVE_GLIB_WITH_SLICE_ALLOCATOR', glib_has_gslice)
-config_host_data.set('HAVE_GLIB_WITH_ALIGNED_ALLOC', glib_has_aligned_alloc)
 config_host_data.set('HAVE_OPENPTY', cc.has_function('openpty', dependencies: util))
 config_host_data.set('HAVE_STRCHRNUL', cc.has_function('strchrnul', prefix: osdep_prefix))
 config_host_data.set('HAVE_SYSTEM_FUNCTION', cc.has_function('system', prefix: '#include <stdlib.h>'))
diff --git a/rust/Cargo.toml b/rust/Cargo.toml
index 9b26aa07cec..d98d2b77026 100644
--- a/rust/Cargo.toml
+++ b/rust/Cargo.toml
@@ -23,7 +23,7 @@ libc = "0.2.162"
 
 [workspace.lints.rust]
 unexpected_cfgs = { level = "deny", check-cfg = [
-    'cfg(MESON)', 'cfg(HAVE_GLIB_WITH_ALIGNED_ALLOC)',
+    'cfg(MESON)',
 ] }
 
 # Occasionally, we may need to silence warnings and clippy lints that
diff --git a/rust/qemu-api/Cargo.toml b/rust/qemu-api/Cargo.toml
index c07a17a28b0..c5ed78035b6 100644
--- a/rust/qemu-api/Cargo.toml
+++ b/rust/qemu-api/Cargo.toml
@@ -21,7 +21,6 @@ libc = { workspace = true }
 
 [features]
 default = ["debug_cell"]
-allocator = []
 debug_cell = []
 
 [lints]
diff --git a/rust/qemu-api/meson.build b/rust/qemu-api/meson.build
index a090297c458..062009f1618 100644
--- a/rust/qemu-api/meson.build
+++ b/rust/qemu-api/meson.build
@@ -2,7 +2,6 @@ _qemu_api_cfg = run_command(rustc_args,
   '--config-headers', config_host_h, '--features', files('Cargo.toml'),
   capture: true, check: true).stdout().strip().splitlines()
 
-# _qemu_api_cfg += ['--cfg', 'feature="allocator"']
 if get_option('debug_mutex')
   _qemu_api_cfg += ['--cfg', 'feature="debug_cell"']
 endif
diff --git a/rust/qemu-api/src/lib.rs b/rust/qemu-api/src/lib.rs
index bcb51c7986a..daa2493bb69 100644
--- a/rust/qemu-api/src/lib.rs
+++ b/rust/qemu-api/src/lib.rs
@@ -36,139 +36,4 @@
 // crate).
 extern crate self as qemu_api;
 
-use std::{
-    alloc::{GlobalAlloc, Layout},
-    ffi::c_void,
-};
-
 pub use error::{Error, Result};
-
-#[cfg(HAVE_GLIB_WITH_ALIGNED_ALLOC)]
-extern "C" {
-    fn g_aligned_alloc0(
-        n_blocks: bindings::gsize,
-        n_block_bytes: bindings::gsize,
-        alignment: bindings::gsize,
-    ) -> bindings::gpointer;
-    fn g_aligned_free(mem: bindings::gpointer);
-}
-
-#[cfg(not(HAVE_GLIB_WITH_ALIGNED_ALLOC))]
-extern "C" {
-    fn qemu_memalign(alignment: usize, size: usize) -> *mut c_void;
-    fn qemu_vfree(ptr: *mut c_void);
-}
-
-extern "C" {
-    fn g_malloc0(n_bytes: bindings::gsize) -> bindings::gpointer;
-    fn g_free(mem: bindings::gpointer);
-}
-
-/// An allocator that uses the same allocator as QEMU in C.
-///
-/// It is enabled by default with the `allocator` feature.
-///
-/// To set it up manually as a global allocator in your crate:
-///
-/// ```ignore
-/// use qemu_api::QemuAllocator;
-///
-/// #[global_allocator]
-/// static GLOBAL: QemuAllocator = QemuAllocator::new();
-/// ```
-#[derive(Clone, Copy, Debug)]
-#[repr(C)]
-pub struct QemuAllocator {
-    _unused: [u8; 0],
-}
-
-#[cfg_attr(all(feature = "allocator", not(test)), global_allocator)]
-pub static GLOBAL: QemuAllocator = QemuAllocator::new();
-
-impl QemuAllocator {
-    // From the glibc documentation, on GNU systems, malloc guarantees 16-byte
-    // alignment on 64-bit systems and 8-byte alignment on 32-bit systems. See
-    // https://www.gnu.org/software/libc/manual/html_node/Malloc-Examples.html.
-    // This alignment guarantee also applies to Windows and Android. On Darwin
-    // and OpenBSD, the alignment is 16 bytes on both 64-bit and 32-bit systems.
-    #[cfg(all(
-        target_pointer_width = "32",
-        not(any(target_os = "macos", target_os = "openbsd"))
-    ))]
-    pub const DEFAULT_ALIGNMENT_BYTES: Option<usize> = Some(8);
-    #[cfg(all(
-        target_pointer_width = "64",
-        not(any(target_os = "macos", target_os = "openbsd"))
-    ))]
-    pub const DEFAULT_ALIGNMENT_BYTES: Option<usize> = Some(16);
-    #[cfg(all(
-        any(target_pointer_width = "32", target_pointer_width = "64"),
-        any(target_os = "macos", target_os = "openbsd")
-    ))]
-    pub const DEFAULT_ALIGNMENT_BYTES: Option<usize> = Some(16);
-    #[cfg(not(any(target_pointer_width = "32", target_pointer_width = "64")))]
-    pub const DEFAULT_ALIGNMENT_BYTES: Option<usize> = None;
-
-    pub const fn new() -> Self {
-        Self { _unused: [] }
-    }
-}
-
-impl Default for QemuAllocator {
-    fn default() -> Self {
-        Self::new()
-    }
-}
-
-// Sanity check.
-const _: [(); 8] = [(); ::core::mem::size_of::<*mut c_void>()];
-
-unsafe impl GlobalAlloc for QemuAllocator {
-    unsafe fn alloc(&self, layout: Layout) -> *mut u8 {
-        if matches!(Self::DEFAULT_ALIGNMENT_BYTES, Some(default) if default.checked_rem(layout.align()) == Some(0))
-        {
-            // SAFETY: g_malloc0() is safe to call.
-            unsafe { g_malloc0(layout.size().try_into().unwrap()).cast::<u8>() }
-        } else {
-            #[cfg(HAVE_GLIB_WITH_ALIGNED_ALLOC)]
-            {
-                // SAFETY: g_aligned_alloc0() is safe to call.
-                unsafe {
-                    g_aligned_alloc0(
-                        layout.size().try_into().unwrap(),
-                        1,
-                        layout.align().try_into().unwrap(),
-                    )
-                    .cast::<u8>()
-                }
-            }
-            #[cfg(not(HAVE_GLIB_WITH_ALIGNED_ALLOC))]
-            {
-                // SAFETY: qemu_memalign() is safe to call.
-                unsafe { qemu_memalign(layout.align(), layout.size()).cast::<u8>() }
-            }
-        }
-    }
-
-    unsafe fn dealloc(&self, ptr: *mut u8, layout: Layout) {
-        if matches!(Self::DEFAULT_ALIGNMENT_BYTES, Some(default) if default.checked_rem(layout.align()) == Some(0))
-        {
-            // SAFETY: `ptr` must have been allocated by Self::alloc thus a valid
-            // glib-allocated pointer, so `g_free`ing is safe.
-            unsafe { g_free(ptr.cast::<_>()) }
-        } else {
-            #[cfg(HAVE_GLIB_WITH_ALIGNED_ALLOC)]
-            {
-                // SAFETY: `ptr` must have been allocated by Self::alloc thus a valid aligned
-                // glib-allocated pointer, so `g_aligned_free`ing is safe.
-                unsafe { g_aligned_free(ptr.cast::<_>()) }
-            }
-            #[cfg(not(HAVE_GLIB_WITH_ALIGNED_ALLOC))]
-            {
-                // SAFETY: `ptr` must have been allocated by Self::alloc thus a valid aligned
-                // glib-allocated pointer, so `qemu_vfree`ing is safe.
-                unsafe { qemu_vfree(ptr.cast::<_>()) }
-            }
-        }
-    }
-}
-- 
2.51.0