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

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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: 90e53c5e70 ("rust: add pin-init API core")
Cc: <stable@vger.kernel.org> # 6.6.y, 6.12.y: 42415d163e: 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: Benno Lossin <lossin@kernel.org>
Reviewed-by: Gary 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: Miguel Ojeda <ojeda@kernel.org>
This commit is contained in:
Benno Lossin
2026-03-02 15:04:15 +01:00
committed by Miguel Ojeda
parent a075082a15
commit 580cc37b1d
1 changed files with 8 additions and 0 deletions
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8
rust/pin-init/internal/src/init.rs
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@@ -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}");
(