Re: [tip:objtool/core 8/12] vmlinux.o: warning: objtool: rust_begin_unwind+0x5c: rust_helper_BUG() is missing a __noreturn annotation

[Josh Poimboeuf <jpoimboe@kernel.org>]

Hi Miguel, Wedson,

Objtool detected that rust_helper_BUG() doesn't return, and seems to be
missing a __noreturn.  But it actually *does* have __noreturn.  The
problem is actually that its rust callees don't seem to know that, i.e.
they assume it returns.

After a little digging I found this comment in rust panic():

    unsafe { bindings::BUG() };
    // Bindgen currently does not recognize `__noreturn` so `BUG` returns `()`
    // instead of `!`. See <https://github.com/rust-lang/rust-bindgen/issues/2094>.
    loop {}

So it seems to be an issue with bindgen, though that github issue has
been resolved.  Any idea when this will show up in a toolchain?

In the meantime we may have to get objtool to manually silence the
warning, unless you have any better ideas.

On Wed, Jun 07, 2023 at 04:57:42AM +0800, kernel test robot wrote:
> tree:   https://git.kernel.org/pub/scm/linux/kernel/git/tip/tip.git objtool/core
> head:   ff9a6459bbec06df7da2545020d7383aba13b3fb
> commit: fedb724c3db5490234ddde0103811c28c2fedae0 [8/12] objtool: Detect missing __noreturn annotations
> config: x86_64-randconfig-a012-20230606 (https://download.01.org/0day-ci/archive/20230607/202306070408.EFxuDoRs-lkp@intel.com/config)
> compiler: clang version 15.0.7 (https://github.com/llvm/llvm-project.git 8dfdcc7b7bf66834a761bd8de445840ef68e4d1a)
> reproduce (this is a W=1 build):
>         mkdir -p ~/bin
>         wget https://raw.githubusercontent.com/intel/lkp-tests/master/sbin/make.cross -O ~/bin/make.cross
>         chmod +x ~/bin/make.cross
>         # https://git.kernel.org/pub/scm/linux/kernel/git/tip/tip.git/commit/?id=fedb724c3db5490234ddde0103811c28c2fedae0
>         git remote add tip https://git.kernel.org/pub/scm/linux/kernel/git/tip/tip.git
>         git fetch --no-tags tip objtool/core
>         git checkout fedb724c3db5490234ddde0103811c28c2fedae0
>         # save the config file
>         mkdir build_dir && cp config build_dir/.config
>         COMPILER_INSTALL_PATH=$HOME/0day COMPILER=clang ~/bin/make.cross W=1 O=build_dir ARCH=x86_64 olddefconfig
>         COMPILER_INSTALL_PATH=$HOME/0day COMPILER=clang ~/bin/make.cross W=1 O=build_dir ARCH=x86_64 SHELL=/bin/bash
> 
> If you fix the issue, kindly add following tag where applicable
> | Reported-by: kernel test robot <lkp@intel.com>
> | Closes: https://lore.kernel.org/oe-kbuild-all/202306070408.EFxuDoRs-lkp@intel.com/
> 
> All warnings (new ones prefixed by >>):
> 
> >> vmlinux.o: warning: objtool: rust_begin_unwind+0x5c: rust_helper_BUG() is missing a __noreturn annotation
> 
> 
> objdump-func vmlinux.o rust_begin_unwind:
> 0000 00000000000b9e69 <rust_begin_unwind>:
> 0000    b9e69:	48 83 ec 48          	sub    $0x48,%rsp
> 0004    b9e6d:	48 89 e0             	mov    %rsp,%rax
> 0007    b9e70:	48 89 38             	mov    %rdi,(%rax)
> 000a    b9e73:	48 8d 4c 24 08       	lea    0x8(%rsp),%rcx
> 000f    b9e78:	48 89 01             	mov    %rax,(%rcx)
> 0012    b9e7b:	48 c7 41 08 00 00 00 00 	movq   $0x0,0x8(%rcx)	b9e7f: R_X86_64_32S	_RNvXsR_NtCs3yuwAp0waWO_4core3fmtRNtNtNtB7_5panic10panic_info9PanicInfoNtB5_7Display3fmtCsfATHBUcknU9_6kernel
> 001a    b9e83:	48 8d 54 24 18       	lea    0x18(%rsp),%rdx
> 001f    b9e88:	48 c7 02 00 00 00 00 	movq   $0x0,(%rdx)	b9e8b: R_X86_64_32S	.rodata+0x137d8
> 0026    b9e8f:	48 c7 42 08 02 00 00 00 	movq   $0x2,0x8(%rdx)
> 002e    b9e97:	48 c7 42 10 00 00 00 00 	movq   $0x0,0x10(%rdx)
> 0036    b9e9f:	48 89 4a 20          	mov    %rcx,0x20(%rdx)
> 003a    b9ea3:	48 c7 42 28 01 00 00 00 	movq   $0x1,0x28(%rdx)
> 0042    b9eab:	48 c7 c7 00 00 00 00 	mov    $0x0,%rdi	b9eae: R_X86_64_32S	_RNvNtNtCsfATHBUcknU9_6kernel5print14format_strings5EMERG
> 0049    b9eb2:	48 c7 c6 00 00 00 00 	mov    $0x0,%rsi	b9eb5: R_X86_64_32S	.rodata+0x13568
> 0050    b9eb9:	31 c0                	xor    %eax,%eax
> 0052    b9ebb:	e8 00 00 00 00       	call   b9ec0 <rust_begin_unwind+0x57>	b9ebc: R_X86_64_PLT32	_printk-0x4
> 0057    b9ec0:	e8 00 00 00 00       	call   b9ec5 <rust_begin_unwind+0x5c>	b9ec1: R_X86_64_PLT32	rust_helper_BUG-0x4
> 005c    b9ec5:	eb fe                	jmp    b9ec5 <rust_begin_unwind+0x5c>
> 
> -- 
> 0-DAY CI Kernel Test Service
> https://github.com/intel/lkp-tests/wiki

-- 
Josh