Re: Live Patching Microconference at Linux Plumbers

[Josh Poimboeuf <jpoimboe@kernel.org>]

On Fri, Apr 14, 2023 at 09:04:36PM +0200, Miguel Ojeda wrote:
> On Fri, Apr 14, 2023 at 7:12 PM Josh Poimboeuf <jpoimboe@kernel.org> wrote:
> >
> > Not to mention how objtool will react to compiled rust code (has it
> > already been tried?)
> 
> Rust uses LLVM, so it should be generally fine -- at least some of the
> checks appear to work. For instance, I can trigger:
> 
>       RUSTC L rust/kernel.o
>     rust/kernel.o: warning: objtool: .text+0x0: unreachable instruction
> 
>       RUSTC [M] samples/rust/rust_minimal.o
>     samples/rust/rust_minimal.o: warning: objtool:
> _R..._6kernel6Module4init+0x172: unreachable instruction
> 
> via a random instruction in the middle of nowhere in the former (with
> `global_asm!`) and a jumped-over instruction in the latter (with
> `asm!`).
> 
> Moreover, we were already getting warnings when rethunk / x86 IBT is
> enabled (since we got `objtool` called for `vmlinux.o`), e.g.
> 
>     vmlinux.o: warning: objtool: .rodata+0x18c58: data relocation to
> !ENDBR: _R...IsWhitespaceEEB4_+0x0
> 
>     vmlinux.o: warning: objtool: _R...into_foreign+0x5: 'naked' return
> found in RETHUNK build
> 
> I can send the patch to run it for all Rust object files via
> `$(cmd_objtool)`, unless you think it is a bad idea.

That's good to hear that it seems to just work.  Feel free to send a
patch to enable it for Rust objects, though I may need your help if we
see any odd warnings ;-)

-- 
Josh