Linux Kernel Module blog-post example broken due to `_Generic`

[SheldonHH]

by following the guide from https://immunant.com/blog/2020/06/kernel_modules/ from @Immunant

Using hypervisor 2.1: https://github.com/Bareflank/hypervisor/tree/v2.1/bfdriver/src/platform/linux

C2Rust with errors

 c2rust transpile ./compile_commands.json --emit-no-std --emit-modules -o bareflank-rs "$@" >output.txt 2>error.txt

complete error.txt

....
789 warnings generated.
....

warning: Missing child 94376710043688 of node AstNode { tag: TagIfStmt, children: [Some(94376710043688), Some(94376710044128), Some(94376710044280)], loc: SrcSpan { fileid: 303, begin_line: 208, begin_column: 9, end_line: 208, end_column: 9 }, type_id: None, rvalue: LValue, macro_expansions: [], macro_expansion_text: None, extras: [] }
Exported Clang AST was invalid. Check warnings above for unimplemented features.
--> /usr/src/linux-hwe-5.19-headers-5.19.0-46/include/linux/page-flags.h:208:9
 [-Wclang-ast]
warning: Missing type 94376706267776 for node: AstNode { tag: TagVarDecl, children: [Some(94376718175144)], loc: SrcSpan { fileid: 54, begin_line: 320, begin_column: 2, end_line: 320, end_column: 2 }, type_id: Some(94376706267776), rvalue: LValue, macro_expansions: [], macro_expansion_text: None, extras: [Text("__flags"), Bool(false), Bool(false), Bool(false), Bool(true), Array([])] }
Exported Clang AST was invalid. Check warnings above for unimplemented features.
--> /usr/src/linux-hwe-5.19-headers-5.19.0-46/include/linux/kernfs.h:320:2
 [-Wclang-ast]
warning: Missing child 94376725014288 of node AstNode { tag: TagParenExpr, children: [Some(94376725014288)], loc: SrcSpan { fileid: 111, begin_line: 386, begin_column: 9, end_line: 386, end_column: 9 }, type_id: Some(94376712495840), rvalue: LValue, macro_expansions: [], macro_expansion_text: None, extras: [] }
Exported Clang AST was invalid. Check warnings above for unimplemented features.
--> /usr/src/linux-hwe-5.19-headers-5.19.0-46/include/linux/memcontrol.h:386:9
 [-Wclang-ast]
warning: Missing child 94376723681448 of node AstNode { tag: TagParenExpr, children: [Some(94376723681448)], loc: SrcSpan { fileid: 53, begin_line: 784, begin_column: 9, end_line: 784, end_column: 9 }, type_id: Some(94376695008912), rvalue: RValue, macro_expansions: [], macro_expansion_text: None, extras: [] }
Exported Clang AST was invalid. Check warnings above for unimplemented features.
--> /usr/src/linux-hwe-5.19-headers-5.19.0-46/include/linux/cgroup-defs.h:784:9
 [-Wclang-ast]
warning: Missing child 94376703345864 of node AstNode { tag: TagIfStmt, children: [Some(94376703345864), Some(94376703346344), Some(94376703346592)], loc: SrcSpan { fileid: 233, begin_line: 382, begin_column: 6, end_line: 382, end_column: 6 }, type_id: None, rvalue: LValue, macro_expansions: [], macro_expansion_text: None, extras: [] }
Exported Clang AST was invalid. Check warnings above for unimplemented features.
--> /usr/src/linux-hwe-5.19-headers-5.19.0-46/arch/x86/include/asm/nospec-branch.h:382:6
 [-Wclang-ast]
thread 'main' panicked at 'Could not find CTypeId(47553) in TypedAstContext', /root/.cargo/registry/src/github.com-1ecc6299db9ec823/c2rust-transpile-0.18.0/src/c_ast/mod.rs:260:30
note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace

total 57 headers files in the warning message

 grep -- "-->" error.txt | awk -F ':' '{print $1}' | sort -u | wc -l

result:

--> /usr/src/linux-hwe-5.19-headers-5.19.0-46/arch/x86/include/asm/atomic64_64.h
--> /usr/src/linux-hwe-5.19-headers-5.19.0-46/arch/x86/include/asm/atomic.h
--> /usr/src/linux-hwe-5.19-headers-5.19.0-46/arch/x86/include/asm/nospec-branch.h
--> /usr/src/linux-hwe-5.19-headers-5.19.0-46/arch/x86/include/asm/pkru.h
--> /usr/src/linux-hwe-5.19-headers-5.19.0-46/arch/x86/include/asm/qspinlock.h
--> /usr/src/linux-hwe-5.19-headers-5.19.0-46/include/asm-generic/rwonce.h
--> /usr/src/linux-hwe-5.19-headers-5.19.0-46/include/linux/atomic/atomic-arch-fallback.h
--> /usr/src/linux-hwe-5.19-headers-5.19.0-46/include/linux/backing-dev-defs.h
--> /usr/src/linux-hwe-5.19-headers-5.19.0-46/include/linux/bio.h
--> /usr/src/linux-hwe-5.19-headers-5.19.0-46/include/linux/bottom_half.h
--> /usr/src/linux-hwe-5.19-headers-5.19.0-46/include/linux/bvec.h
--> /usr/src/linux-hwe-5.19-headers-5.19.0-46/include/linux/cgroup-defs.h
--> /usr/src/linux-hwe-5.19-headers-5.19.0-46/include/linux/cgroup.h
--> /usr/src/linux-hwe-5.19-headers-5.19.0-46/include/linux/dcache.h
--> /usr/src/linux-hwe-5.19-headers-5.19.0-46/include/linux/device.h
--> /usr/src/linux-hwe-5.19-headers-5.19.0-46/include/linux/fs.h
--> /usr/src/linux-hwe-5.19-headers-5.19.0-46/include/linux/highmem.h
--> /usr/src/linux-hwe-5.19-headers-5.19.0-46/include/linux/hrtimer.h
--> /usr/src/linux-hwe-5.19-headers-5.19.0-46/include/linux/huge_mm.h
--> /usr/src/linux-hwe-5.19-headers-5.19.0-46/include/linux/idr.h
--> /usr/src/linux-hwe-5.19-headers-5.19.0-46/include/linux/kernfs.h
--> /usr/src/linux-hwe-5.19-headers-5.19.0-46/include/linux/key.h
--> /usr/src/linux-hwe-5.19-headers-5.19.0-46/include/linux/kobject.h
--> /usr/src/linux-hwe-5.19-headers-5.19.0-46/include/linux/ktime.h
--> /usr/src/linux-hwe-5.19-headers-5.19.0-46/include/linux/list_bl.h
--> /usr/src/linux-hwe-5.19-headers-5.19.0-46/include/linux/list.h
--> /usr/src/linux-hwe-5.19-headers-5.19.0-46/include/linux/llist.h
--> /usr/src/linux-hwe-5.19-headers-5.19.0-46/include/linux/math64.h
--> /usr/src/linux-hwe-5.19-headers-5.19.0-46/include/linux/memcontrol.h
--> /usr/src/linux-hwe-5.19-headers-5.19.0-46/include/linux/mm.h
--> /usr/src/linux-hwe-5.19-headers-5.19.0-46/include/linux/mmzone.h
--> /usr/src/linux-hwe-5.19-headers-5.19.0-46/include/linux/mount.h
--> /usr/src/linux-hwe-5.19-headers-5.19.0-46/include/linux/page-flags.h
--> /usr/src/linux-hwe-5.19-headers-5.19.0-46/include/linux/pagemap.h
--> /usr/src/linux-hwe-5.19-headers-5.19.0-46/include/linux/page_ref.h
--> /usr/src/linux-hwe-5.19-headers-5.19.0-46/include/linux/percpu_counter.h
--> /usr/src/linux-hwe-5.19-headers-5.19.0-46/include/linux/percpu-refcount.h
--> /usr/src/linux-hwe-5.19-headers-5.19.0-46/include/linux/pgtable.h
--> /usr/src/linux-hwe-5.19-headers-5.19.0-46/include/linux/plist.h
--> /usr/src/linux-hwe-5.19-headers-5.19.0-46/include/linux/radix-tree.h
--> /usr/src/linux-hwe-5.19-headers-5.19.0-46/include/linux/rbtree_latch.h
--> /usr/src/linux-hwe-5.19-headers-5.19.0-46/include/linux/rculist_bl.h
--> /usr/src/linux-hwe-5.19-headers-5.19.0-46/include/linux/rcupdate.h
--> /usr/src/linux-hwe-5.19-headers-5.19.0-46/include/linux/rcu_sync.h
--> /usr/src/linux-hwe-5.19-headers-5.19.0-46/include/linux/rcuwait.h
--> /usr/src/linux-hwe-5.19-headers-5.19.0-46/include/linux/sched.h
--> /usr/src/linux-hwe-5.19-headers-5.19.0-46/include/linux/sched/signal.h
--> /usr/src/linux-hwe-5.19-headers-5.19.0-46/include/linux/seqlock.h
--> /usr/src/linux-hwe-5.19-headers-5.19.0-46/include/linux/srcu.h
--> /usr/src/linux-hwe-5.19-headers-5.19.0-46/include/linux/swap.h
--> /usr/src/linux-hwe-5.19-headers-5.19.0-46/include/linux/thread_info.h
--> /usr/src/linux-hwe-5.19-headers-5.19.0-46/include/linux/timerqueue.h
--> /usr/src/linux-hwe-5.19-headers-5.19.0-46/include/linux/uaccess.h
--> /usr/src/linux-hwe-5.19-headers-5.19.0-46/include/linux/wait.h
--> /usr/src/linux-hwe-5.19-headers-5.19.0-46/include/linux/workqueue.h
--> /usr/src/linux-hwe-5.19-headers-5.19.0-46/include/linux/writeback.h
--> /usr/src/linux-hwe-5.19-headers-5.19.0-46/include/linux/xarray.h

[fw-immunant]

The relevant warning from your log appears to be:

warning: c2rust: Encountered unsupported generic selection expression

Which is caused by the definition of the page_folio macro in the kernel, which uses _Generic. This is tracked by issue #760.

[SheldonHH]

Thank you. I am curious as to how the conversion of the Linux Kernel Module to C2Rust was successful back in 2020. https://immunant.com/blog/2020/06/kernel_modules/

What versions of C2Rust, Clang, GCC, and the Linux kernel were used in this process? the article is a bit vague about the specific versions of tools.

I'd like to replicate the same successful transpilation, and use C2Rust to translate more simple Linux Kernel Modules to improve on C2Rust.

[brechtvandesijpe]

Thank you. I am curious as to how the conversion of the Linux Kernel Module to C2Rust was successful back in 2020. https://immunant.com/blog/2020/06/kernel_modules/

What versions of C2Rust, Clang, GCC, and the Linux kernel were used in this process? the article is a bit vague about the specific versions of tools.

I'd like to replicate the same successful transpilation, and use C2Rust to translate more simple Linux Kernel Modules to improve on C2Rust.

I am currently having the same issue, following the same tutorial. I wonder what these steps were:

"After making some fixes and additions to C2Rust and fix the subsequent compilation errors, we compiled the resulting Rust code with:"

It seems that in the tutorial the author was able to fix these. Did you find any solution to the problem?

[thedataking]

Hi @brechtvandesijpe, the issue is missing support for _Generic types as mentioned here https://github.com/immunant/c2rust/issues/982#issuecomment-1630869003

@ahomescu do you remember how/whether we worked around this issue?

[ahomescu]

I don't remember anything about _Generic. Keep in mind this was 4 years ago, so it's very likely that the kernel code has also changed significantly. I didn't document the exact versions of Linux or clang that we used, but the blog post mentions 5.0.

[ahomescu]

The relevant warning from your log appears to be:

warning: c2rust: Encountered unsupported generic selection expression

Which is caused by the definition of the page_folio macro in the kernel, which uses _Generic. This is tracked by issue #760.

It looks like page_folio was introduced in Linux 5.16, so any kernel before that should be good (unless there are other uses of _Generic).