感谢:)

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👇
苦瓜小仔: The Most Annoying Bug I've Had To Track Down

I recently had this https://github.com/Morganamilo/paru/issues/392 bug reported to me.

The user came at me with a full backtrace so I thought it would be an easy fix. The bug appeared to be in the c bindings I was using, so clearly there's some subtle UB/error not being handled somewhere.

Yet I couldn't find anything wrong. No matter how many null checks and assertions I put around the place.

Then I figured out what wrong: https://github.com/archlinux/alpm.rs/commit/5253d6

Perviously, when getting a pointer to a union the code did

let inner = &mut unsafe { (*self.inner).replace } 

Due to the &mut being outside the unsafe block this actually takes a reference to a temporary variables instead of the union filed.

It effectively looks like:

let tmp = unsafe { (*self.inner).replace };
let inner = &mut tmp //reference to stack data 

The fix is to just move the &mut into the unsafe block, making rust not create a temporary variable and actually reference the union.

This is the first time rust has let me footgun myself.

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👇
Neutron3529:

https://www.reddit.com/r/rust/comments/nqjyb7/the_most_annoying_bug_ive_had_to_track_down/

能体谅一下墙内的读者，给个简介吗

实在不想找梯子……

The Most Annoying Bug I've Had To Track Down

I recently had this https://github.com/Morganamilo/paru/issues/392 bug reported to me.

The user came at me with a full backtrace so I thought it would be an easy fix. The bug appeared to be in the c bindings I was using, so clearly there's some subtle UB/error not being handled somewhere.

Yet I couldn't find anything wrong. No matter how many null checks and assertions I put around the place.

Then I figured out what wrong: https://github.com/archlinux/alpm.rs/commit/5253d6

Perviously, when getting a pointer to a union the code did

let inner = &mut unsafe { (*self.inner).replace } 

Due to the &mut being outside the unsafe block this actually takes a reference to a temporary variables instead of the union filed.

It effectively looks like:

let tmp = unsafe { (*self.inner).replace };
let inner = &mut tmp //reference to stack data 

The fix is to just move the &mut into the unsafe block, making rust not create a temporary variable and actually reference the union.

This is the first time rust has let me footgun myself.

--
👇
Neutron3529:

https://www.reddit.com/r/rust/comments/nqjyb7/the_most_annoying_bug_ive_had_to_track_down/

能体谅一下墙内的读者，给个简介吗

实在不想找梯子……

https://www.reddit.com/r/rust/comments/nqjyb7/the_most_annoying_bug_ive_had_to_track_down/

能体谅一下墙内的读者，给个简介吗

实在不想找梯子……

这个编辑器有意思 哈哈