Commit 580cc37b authored by Benno Lossin's avatar Benno Lossin Committed by Miguel Ojeda
Browse files

rust: pin-init: internal: init: document load-bearing fact of field accessors 

The functions `[Pin]Init::__[pinned_]init` and `ptr::write` called from
the `init!` macro require the passed pointer to be aligned. This fact is
ensured by the creation of field accessors to previously initialized
fields.

Since we missed this very important fact from the beginning [1],
document it in the code.

Link: https://rust-for-linux.zulipchat.com/#narrow/channel/561532-pin-init/topic/initialized.20field.20accessor.20detection/with/576210658

 [1]
Fixes: 90e53c5e ("rust: add pin-init API core")
Cc: <stable@vger.kernel.org> # 6.6.y, 6.12.y: 42415d16: rust: pin-init: add references to previously initialized fields
Cc: <stable@vger.kernel.org> # 6.6.y, 6.12.y, 6.18.y, 6.19.y
Signed-off-by: default avatarBenno Lossin <lossin@kernel.org>
Reviewed-by: default avatarGary Guo <gary@garyguo.net>
Link: https://patch.msgid.link/20260302140424.4097655-2-lossin@kernel.org


[ Updated Cc: stable@ tags as discussed. - Miguel ]
Signed-off-by: default avatarMiguel Ojeda <ojeda@kernel.org>
parent a075082a

rust/pin-init/internal/src/init.rs

+8 −0
Original line number Diff line number Diff line
@@ -251,6 +251,10 @@ fn init_fields( 
                });

                // Again span for better diagnostics

                let write = quote_spanned!(ident.span()=> ::core::ptr::write);

                // NOTE: the field accessor ensures that the initialized field is properly aligned.

                // Unaligned fields will cause the compiler to emit E0793. We do not support

                // unaligned fields since `Init::__init` requires an aligned pointer; the call to

                // `ptr::write` below has the same requirement.

                let accessor = if pinned {

                    let project_ident = format_ident!("__project_{ident}");

                    quote! {
@@ -278,6 +282,10 @@ fn init_fields( 
            InitializerKind::Init { ident, value, .. } => {

                // Again span for better diagnostics

                let init = format_ident!("init", span = value.span());

                // NOTE: the field accessor ensures that the initialized field is properly aligned.

                // Unaligned fields will cause the compiler to emit E0793. We do not support

                // unaligned fields since `Init::__init` requires an aligned pointer; the call to

                // `ptr::write` below has the same requirement.

                let (value_init, accessor) = if pinned {

                    let project_ident = format_ident!("__project_{ident}");

                    (