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

[Alex Gaynor]

The fix to properly handle noreturn is present in bindgen > 0.61.0.
Per min-tool-version.sh, we currently only require bindgen 0.56.0 or
newer.

I'm not sure if there are obstacles to requiring a newer bindgen
version, at which point the loop {} would not be required.

Cheers,
Alex

On Tue, Jun 6, 2023 at 5:52 PM Josh Poimboeuf <jpoimboe@xxxxxxxxxx> wrote:
>
> 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@xxxxxxxxx/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@xxxxxxxxx>
> > | Closes: https://lore.kernel.org/oe-kbuild-all/202306070408.EFxuDoRs-lkp@xxxxxxxxx/
> >
> > 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



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