48 lines
1.8 KiB
Diff
48 lines
1.8 KiB
Diff
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From 03fe93ad1f5a5d8f3a132ea419e4a509069e2130 Mon Sep 17 00:00:00 2001
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From: ace yan <yan_ace62@126.com>
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Date: Sun, 20 Feb 2022 14:57:34 +0800
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Subject: [PATCH 01/10] Implement a safe offset_of macro function
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MIME-Version: 1.0
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Content-Type: text/plain; charset=UTF-8
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Content-Transfer-Encoding: 8bit
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Original offset_of macro implementation reference to packed field is unaligned，
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and creating a misaligned reference is undefined behavior。
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In the higher version of the rustc compiler,
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there will be a compilation warning prompt: this was previously accepted by the compiler
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but is being phased out; it will become a hard error in a future release!
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Signed-off-by: Yan Wen <yan_ace62@126.com>
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---
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util/src/offsetof.rs | 14 +++++++++++---
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1 file changed, 11 insertions(+), 3 deletions(-)
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diff --git a/util/src/offsetof.rs b/util/src/offsetof.rs
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index c2696c8..a6b55d8 100644
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--- a/util/src/offsetof.rs
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+++ b/util/src/offsetof.rs
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@@ -13,9 +13,17 @@
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/// Macro: Calculate offset of specified field in a type.
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#[macro_export]
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macro_rules! __offset_of {
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- ($type_name:ty, $field:ident) => {
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- unsafe { &(*(std::ptr::null::<$type_name>())).$field as *const _ as usize }
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- };
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+ ($type_name:ty, $field:ident) => {{
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+ let tmp = core::mem::MaybeUninit::<$type_name>::uninit();
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+ let outer = tmp.as_ptr();
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+ // Safe because the pointer is valid and aligned, just not initialised; `addr_of` ensures that
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+ // we don't actually read from `outer` (which would be UB) nor create an intermediate reference.
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+ let inner = unsafe { core::ptr::addr_of!((*outer).$field) } as *const u8;
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+ // Safe because the two pointers are within the same allocation block.
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+ unsafe {
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+ inner.offset_from(outer as *const u8) as usize
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+ }
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+ }};
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}
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/// Macro: Calculate offset of a field in a recursive type.
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--
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2.25.1
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