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Diffstat (limited to 'drivers/gpu/drm/asahi/place.rs')
| -rw-r--r-- | drivers/gpu/drm/asahi/place.rs | 343 |
1 files changed, 343 insertions, 0 deletions
diff --git a/drivers/gpu/drm/asahi/place.rs b/drivers/gpu/drm/asahi/place.rs new file mode 100644 index 000000000000..40c51f4fab8d --- /dev/null +++ b/drivers/gpu/drm/asahi/place.rs @@ -0,0 +1,343 @@ +// SPDX-License-Identifier: Apache-2.0 OR MIT + +//! "Placement new" macro +//! +//! This cursed abomination of a declarative macro is used to emulate a "placement new" feature, +//! which allows initializing objects directly in a user-provided memory region without first +//! going through the stack. +//! +//! This driver needs to manage several large GPU objects of a fixed layout. Linux kernel stacks are +//! very small, so it is impossible to create these objects on the stack. While the compiler can +//! sometimes optimize away the stack copy and directly instantiate in target memory, this is not +//! guaranteed and not reliable. Therefore, we need some mechanism to ergonomically initialize +//! complex structures directly in a pre-allocated piece of memory. +//! +//! This issue also affects some driver-internal structs which are large/complex enough to overflow +//! the stack. While this can be solved by breaking them up into pieces and using `Box` more +//! liberally, this has performance implications and still isn't very nice. This macro can also be +//! used to solve this issue. +//! +//! # Further reading +//! https://github.com/rust-lang/rust/issues/27779#issuecomment-378416911 +//! https://internals.rust-lang.org/t/removal-of-all-unstable-placement-features/7223 + +/// Initialize a `MaybeUninit` in-place, without constructing the value on the stack first. +/// +/// This macro is analogous to `MaybeUninit::write()`. In other words, +/// `place!(foo, bar)` is equivalent to `MaybeUninit::write(foo, bar)`, except that `bar` is not +/// constructed first, but rather its fields (if it is a structure constructor) are copied one by +/// one into the correct location in the `MaybeUninit`. +/// +/// The macro supports most Rust initialization syntax including type paths, generic arguments, +/// and nested structures. Nested structures are themselves initialized in-place field by field. +/// `..Default::default()` is supported, but this macro converts it to `..Zeroed::zeroed()`, as it +/// initializes those structs by zero-initializing the underlying memory. Usage of +/// `..Default::default()` with a type not implementing `Zeroed` will result in a compile error. +/// +/// Usage: +/// ``` +/// let mut buf = MaybeUninit::uninit(); +/// let mut_ref = place!(&mut buf, MyStruct { +/// b: true, +/// s: String::from("works"), +/// i: str::parse::<i32>("123").unwrap(), +/// v: vec![String::from("works")], +/// x: foo::MyOtherCoolStruct { +/// a: false, +/// b: String::from("Hello, world!"), +/// }, +/// y: foo::MyOtherCoolStruct { +/// a: false, +/// b: String::from("Hello, world!"), +/// }, +/// z: foo::MyCoolGenericStruct::<bool, String> { +/// a: false, +/// b: String::from("Hello, world!"), +/// }, +/// }; +/// // `mut_ref` is now a mutable reference to the `buf`, which is now safely initialized. +/// ``` +/// +/// Based on https://crates.io/crates/place by DianaNites, with contributions by Joshua Barretto. +#[macro_export] +macro_rules! place { + // Top-level struct + (@STRUCT $ptr:ident, _TOP, $typ:path, {$($typ_init:tt)*} { $($fields:tt)* }) => {{ + place!(@STRUCT_ZERO $ptr, {$($typ_init)*} { $($fields)* }); + place!(@STRUCT_CHECK $ptr, {$($typ_init)*} { $($fields)* } { + place!(@FIELDS $ptr, $($fields)*); + }); + }}; + // Nested structure + (@STRUCT $ptr:ident, $f_struct:ident, $typ:path, {$($typ_init:tt)*} { $($fields:tt)* }) => {{ + use core::ptr::addr_of_mut; + let buf = unsafe { addr_of_mut!((*$ptr).$f_struct) }; + place!(@STRUCT_ZERO buf, {$($typ_init)*} { $($fields)* }); + place!(@STRUCT_CHECK $ptr, {$($typ_init)*} { $($fields)* } { + place!(@FIELDS buf, $($fields)*); + }); + }}; + + // Zero-initialize structure if the initializer ends in ..default::Default() + (@STRUCT_ZERO $ptr:ident, {$($typ_init:tt)*} { $($f:ident $(: $v:expr)?),* $(,)? }) => {}; + (@STRUCT_ZERO $ptr:ident, {$($typ_init:tt)*} { $($($f:ident $(: $v:expr)?),*,)? ..Default::default() }) => {{ + // Check that the structure actually implements Zeroed + const _: () = { + fn _check_default() { + let _ = $($typ_init)* { + ..Zeroed::zeroed() + }; + } + }; + use core::ptr; + unsafe { ptr::write_bytes($ptr, 0, 1) }; + + }}; + + // Check that all fields are specified + (@STRUCT_CHECK $ptr:ident, {$($typ_init:tt)*} { $($($f:ident $(: $v:expr)?),*,)? ..Default::default() } {$($body:tt)*}) => { + if false { + #[allow(clippy::redundant_field_names)] + let _x = $($typ_init)* { + $($( + $f $(: $v)? + ),* + ,)? + ..Zeroed::zeroed() + }; + } else { + {$($body)*} + } + }; + (@STRUCT_CHECK $ptr:ident, {$($typ_init:tt)*} { $($f:ident $(: $v:expr)?),* $(,)? } {$($body:tt)*}) => { + if false { + #[allow(clippy::redundant_field_names)] + let _x = $($typ_init)* { + $( + $f $(: $v)? + ),* + }; + } else { + {$($body)*} + } + }; + // Top-level scalar + (@SCALAR $ptr:ident, _TOP, $val:expr) => { + let tmp = $val; + unsafe { $ptr.write(tmp); } + }; + // Regular field + (@SCALAR $ptr:ident, $f:ident, $val:expr) => {{ + use core::ptr::addr_of_mut; + let tmp = $val; + unsafe { addr_of_mut!((*$ptr).$f).write(tmp); } + }}; + // Type-like name followed by braces is a nested structure + (@PARTIAL $ptr:ident, $f:ident, {$($head:tt)*}, {{ $($fields:tt)* } $($tail:tt)*}) => { + place!(@STRUCT $ptr, $f, $($head)*, {$($head)*} { $($fields)* }); + place!(@FIELDS $ptr $($tail)*) + }; + // Type-like name followed by ::ident, append to head + (@PARTIAL $ptr:ident, $f:ident, {$($head:tt)*}, {::$id:ident $($tail:tt)*}) => { + place!(@PARTIAL $ptr, $f, {$($head)* :: $id}, {$($tail)*}); + }; + // Type-like name followed by ::<args>, append to head + (@PARTIAL $ptr:ident, $f:ident, {$($head:tt)*}, {::<$($gen:ty),*> $($tail:tt)*}) => { + place!(@PARTIAL $ptr, $f, {$($head)* :: <$($gen),*>}, {$($tail)*}); + }; + // Type-like name followed by ::<'lifetime>, append to head + (@PARTIAL $ptr:ident, $f:ident, {$($head:tt)*}, {::<$li:lifetime> $($tail:tt)*}) => { + place!(@PARTIAL $ptr, $f, {$($head)* :: <$li>}, {$($tail)*}); + }; + // Anything else, parse it as an expression + (@PARTIAL $ptr:ident, $f:ident, {$($head:tt)*}, {$($tail:tt)*}) => { + place!(@EXPR $ptr, $f, $($head)* $($tail)*) + }; + // Expression followed by more fields + (@EXPR $ptr:ident, $f:ident, $val:expr, $($tail:tt)*) => { + place!(@SCALAR $ptr, $f, $val); + place!(@FIELDS $ptr, $($tail)*) + }; + // Last field expression, without a trailing comma + (@EXPR $ptr:ident, $f:ident, $val:expr) => { + place!(@SCALAR $ptr, $f, $val); + }; + // Field with a value starting with an ident, start incremental type parsing + (@FIELDS $ptr:ident, $f:ident : $id:ident $($tail:tt)*) => { + place!(@PARTIAL $ptr, $f, {$id}, {$($tail)*}); + }; + // Same, but starting with ::ident + (@FIELDS $ptr:ident, $f:ident : ::$id:ident $($tail:tt)*) => { + place!(@PARTIAL $ptr, $f, {::$id}, {$($tail)*}); + }; + // Otherwise, parse it as an expression + (@FIELDS $ptr:ident, $f:ident : $($tail:tt)*) => { + place!(@EXPR $ptr, $f, $($tail)*) + }; + // Default terminating case + (@FIELDS $ptr:ident, ..Default::default() ) => {}; + // Terminating case + (@FIELDS $ptr:ident $(,)? ) => {}; + ( + $buf:expr, + $($val:tt)* + ) => {{ + use core::mem::MaybeUninit; + // Ensures types are correct + let obj: &mut MaybeUninit<_> = $buf; + let top_ptr = obj.as_mut_ptr(); + place!(@FIELDS top_ptr, _TOP: $($val)*); + // SAFETY: All fields have been initialized above + // The compiler ensures that all fields were used, all types were correct, + // and that size and alignment are correct. + unsafe { obj.assume_init_mut() } + }}; +} + +/// Helper macro to get the struct type part of a struct initialization expression. +#[macro_export] +#[doc(hidden)] +macro_rules! get_type { + ($t:ty { $($val:tt)* }) => { + $t + }; +} + +/// Like `Box::try_new(...)`, but with in-place initialization. +#[macro_export] +macro_rules! box_in_place { + ($($val:tt)*) => {{ + use $crate::place; + let b = Box::<$crate::get_type!($($val)*)>::try_new_uninit(); + match b { + Ok(mut p) => { + place!((&mut *p), $($val)*); + Ok(unsafe { p.assume_init() }) + } + Err(e) => Err(e) + } + }}; +} + +// TODO: figure out how to make this run +#[cfg(test)] +mod tests { + use super::*; + use core::mem::MaybeUninit; + + #[derive(Debug, PartialEq)] + struct MyCoolStruct { + b: bool, + s: String, + i: i32, + v: Vec<String>, + x: MyOtherCoolStruct, + y: MyOtherCoolStruct, + z: foo::MyCoolGenericStruct<bool, String>, + } + + #[derive(Debug, PartialEq)] + struct MyDefaultStruct { + b: bool, + i: i32, + j: i16, + } + default_zeroed!(MyDefaultStruct); + + mod foo { + #[derive(Debug, PartialEq)] + pub struct MyOtherCoolStruct { + pub a: bool, + pub b: String, + } + #[derive(Debug, PartialEq)] + pub struct MyCoolGenericStruct<T, U> { + pub a: T, + pub b: U, + } + } + + use foo::MyOtherCoolStruct; + + #[test] + fn test_initialized() { + let mut buf: MaybeUninit<MyCoolStruct> = MaybeUninit::uninit(); + + let x: &mut MyCoolStruct = place!( + &mut buf, + MyCoolStruct { + b: true, + s: String::from("works"), + i: str::parse::<i32>("123").unwrap(), + v: vec![String::from("works")], + x: MyOtherCoolStruct { + a: false, + b: String::from("Hello, world!"), + }, + y: foo::MyOtherCoolStruct { + a: false, + b: String::from("Hello, world!"), + }, + z: foo::MyCoolGenericStruct::<bool, String> { + a: false, + b: String::from("Hello, world!"), + } + } + ); + //dbg!(x); + + assert_eq!( + x, + &MyCoolStruct { + b: true, + s: String::from("works"), + i: str::parse::<i32>("123").unwrap(), + v: vec![String::from("works")], + x: foo::MyOtherCoolStruct { + a: false, + b: String::from("Hello, world!"), + }, + y: foo::MyOtherCoolStruct { + a: false, + b: String::from("Hello, world!"), + }, + z: foo::MyCoolGenericStruct::<bool, String> { + a: false, + b: String::from("Hello, world!"), + }, + }, + ); + } + + #[test] + fn test_default() { + let mut buf: MaybeUninit<MyDefaultStruct> = MaybeUninit::uninit(); + + let x: &mut MyDefaultStruct = place!( + &mut buf, + MyDefaultStruct { + b: true, + i: 1, + ..Default::default() + } + ); + + assert_eq!( + x, + &MyDefaultStruct { + b: true, + i: 1, + j: 0, + }, + ); + } + + #[test] + fn test_scalar() { + let mut buf: MaybeUninit<u32> = MaybeUninit::uninit(); + + let x: &mut u32 = place!(&mut buf, 1234); + + assert_eq!(x, &mut 1234u32); + } +} |