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qsr opened this issue Jan 6, 2025 · 1 comment · Fixed by #3173
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bindgen with explicit padding generates an array of size 18446744073709551608 #3068

qsr opened this issue Jan 6, 2025 · 1 comment · Fixed by #3173

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@qsr
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qsr commented Jan 6, 2025 •
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When running bindgen with the --explicit-padding option on the following file:

struct Foo {
  union {
    char d0[2];
    char d1[1];
    char d2[0];
  };
};

it ends up generating the following struct:

#[repr(C)]
pub struct Foo__bindgen_ty_1 {
    pub d0: __BindgenUnionField<[::std::os::raw::c_char; 2usize]>,
    pub d1: __BindgenUnionField<[::std::os::raw::c_char; 1usize]>,
    pub d2: __BindgenUnionField<[::std::os::raw::c_char; 0usize]>,
    pub __bindgen_padding_0: [u8; 18446744073709551615usize],
    pub bindgen_union_field: [u8; 2usize],
}

The __bindgen_padding_0 field is a little bit extreme.
qsr pushed a commit to qsr/rust-bindgen that referenced this issue Mar 20, 2025
Fix union layout when it contains 0 sized array.
07b8323 
Fix rust-lang#3068
@qsr qsr mentioned this issue Mar 20, 2025
Merged
qsr pushed a commit to qsr/rust-bindgen that referenced this issue Mar 20, 2025
Fix union layout when it contains 0 sized array.
854359d 
Fix rust-lang#3068
qsr pushed a commit to qsr/rust-bindgen that referenced this issue Mar 20, 2025
Fix union layout when it contains 0 sized array.
b0652e6 
Fix rust-lang#3068
@qsr
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qsr commented Mar 24, 2025

I proposed a fix for this, but I am not sure how I can have it reviewed. The documentation seems to not be up to date because the review bot is not setup.

@emilio ? @pvdrz ?

bherrera pushed a commit to misttech/fuchsia that referenced this issue Apr 1, 2025
@maryx
[starnix] Update generate.py and remove __bindgen_padding_0
3b13071 
This CL 1) updates the outputs of generate.py so that they match what the script does at ToT (outputs such as arm.rs at ToT haven't been updated/synced), and 2) makes sure fx build works after the update.

Steps:
1. Run `./src/starnix/lib/linux_uapi/generate.py` (no edits)
This results in some changes, notably, io_uring_sqe__bindgen_ty_6 updating to a struct and having 5 params.

2. Run `fx build`. This fails due to:
```
error[E0080]: evaluation of `std::mem::size_of::<io_uring_sqe>` failed
 --> /b/s/w/ir/x/w/fuchsia-third_party-rust/library/core/src/mem/mod.rs:1229:26
  |
  = note: values of the type `[u8; 18446744073709551608]` are too big for the target architecture
```
This is rust-lang/rust-bindgen#3068.

3. Patch in the generate.py edit. Run `./src/starnix/lib/linux_uapi/generate.py` (with edit). Note that generated files now do not have the `pub __bindgen_padding_0` line.

4. `fx build` completes.

Once's qsr's fix at rust-lang/rust-bindgen#3173 is merged and rolled in, we shouldn't need to do the regex replace.

Bug: 398914504
Change-Id: Ic6be5a14f4f00477795588a5ed52e5770c64955e
Reviewed-on: https://fuchsia-review.googlesource.com/c/fuchsia/+/1235157
Reviewed-by: Benjamin Lerman <[email protected]>
Commit-Queue: Mary Xia <[email protected]>
bherrera pushed a commit to misttech/integration that referenced this issue Apr 3, 2025
@copybara-github
[roll] Roll fuchsia [starnix] Update generate.py and remove __bindgen…
aaccdee 
…_padding_0

This CL 1) updates the outputs of generate.py so that they match what the script does at ToT (outputs such as arm.rs at ToT haven't been updated/synced), and 2) makes sure fx build works after the update.

Steps:
1. Run `./src/starnix/lib/linux_uapi/generate.py` (no edits)
This results in some changes, notably, io_uring_sqe__bindgen_ty_6 updating to a struct and having 5 params.

2. Run `fx build`. This fails due to:
```
error[E0080]: evaluation of `std::mem::size_of::<io_uring_sqe>` failed
 --> /b/s/w/ir/x/w/fuchsia-third_party-rust/library/core/src/mem/mod.rs:1229:26
  |
  = note: values of the type `[u8; 18446744073709551608]` are too big for the target architecture
```
This is rust-lang/rust-bindgen#3068.

3. Patch in the generate.py edit. Run `./src/starnix/lib/linux_uapi/generate.py` (with edit). Note that generated files now do not have the `pub __bindgen_padding_0` line.

4. `fx build` completes.

Once's qsr's fix at rust-lang/rust-bindgen#3173 is merged and rolled in, we shouldn't need to do the regex replace.

Original-Bug: 398914504
Original-Reviewed-on: https://fuchsia-review.googlesource.com/c/fuchsia/+/1235157
Original-Revision: 3b130710ba6aac0d9130bc718184bfaf34abbfa8
GitOrigin-RevId: c1e0371e35ebae79d27ecaaac3fc16ae30461a38
Change-Id: I4169f94aa0c01a8be2ddcddb6b094e46b6c7108d
github-merge-queue bot pushed a commit that referenced this issue Apr 4, 2025
@emilio
Fix union layout when it contains 0 sized array.
71e7c2b 
Fix #3068
github-merge-queue bot pushed a commit that referenced this issue Apr 4, 2025
@emilio
Fix union layout when it contains 0 sized array.
a50a2cf 
Fix #3068
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Fix union layout when it contains 0 sized array. qsr/rust-bindgen
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@qsr