Re: fs/btrfs/lzo.o: warning: objtool: lzo_compress_folios+0xb0: unreachable instruction

[Philip Li]

On Wed, Jul 24, 2024 at 11:45:42AM +0930, Qu Wenruo wrote:
> 
> 
> 在 2024/7/24 11:32, Philip Li 写道:
> > On Tue, Jul 23, 2024 at 08:18:41PM +0800, kernel test robot wrote:
> > > Hi Qu,
> > > 
> > > FYI, the error/warning was bisected to this commit, please ignore it if it's irrelevant.
> > > 
> > > tree:   https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git master
> > > head:   66ebbdfdeb093e097399b1883390079cd4c3022b
> > > commit: 400b172b8cdcff87038697169fe9e4222120dd9a btrfs: compression: migrate compression/decompression paths to folios
> > > date:   3 months ago
> > > config: loongarch-randconfig-001-20240722 (https://download.01.org/0day-ci/archive/20240723/202407232006.7Gelsbv4-lkp@xxxxxxxxx/config)
> > > compiler: loongarch64-linux-gcc (GCC) 14.1.0
> > > reproduce (this is a W=1 build): (https://download.01.org/0day-ci/archive/20240723/202407232006.7Gelsbv4-lkp@xxxxxxxxx/reproduce)
> > > 
> > > If you fix the issue in a separate patch/commit (i.e. not just a new version of
> > > the same patch/commit), kindly add following tags
> > > | Reported-by: kernel test robot <lkp@xxxxxxxxx>
> > > | Closes: https://lore.kernel.org/oe-kbuild-all/202407232006.7Gelsbv4-lkp@xxxxxxxxx/
> > > 
> > > All warnings (new ones prefixed by >>):
> > 
> > Sorry, kindly ignore this report which could be related to tool chain upgrade to
> > loongarch64-linux-gcc (GCC) 14.1.0.
> > 
> > We will further check whether the issue can be reproduced on gcc-13.
> 
> Gcc 14.1 is totally fine, as that's the version I'm using already (although
> a little newer, 14.1.1)
> 
> It would be even better to focus on more common architectures first (x86_64,
> aarch64), and put a lower priority on less common architectures.

thanks for the suggestion, the bot covers all archs, for the case here,
the commit works fine on x86 or aarch64, and only triggers a bisected report
on loongarch. We will block such false positve report and do a comparison
check whether this specific issue can be reproduced on other compilers, though
we can not quickly tell whether this is toolchain issue or real issue.

> 
> As most developers are not really able to access those platforms easily.
> 
> Thanks,
> Qu
> 
> > 
> > > 
> > > > > fs/btrfs/lzo.o: warning: objtool: lzo_compress_folios+0xb0: unreachable instruction
> > >     fs/btrfs/lzo.o: warning: objtool: lzo_decompress_bio+0x140: unreachable instruction
> > > 
> > > 
> > > objdump-func vmlinux.o lzo_compress_folios:
> > > 
> > > -- 
> > > 0-DAY CI Kernel Test Service
> > > https://github.com/intel/lkp-tests/wiki
> > >