Re: arch/mips/boot/compressed/decompress.c:undefined reference to `__ashldi3'

[Pedro Falcato]

On Wed, Sep 30, 2026 at 12:01:59PM -0700, Andrew Morton wrote:
> On Wed, 30 Sep 2026 18:36:50 +0200 kernel test robot <lkp@xxxxxxxxx> wrote:
> 
> > tree:   https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git master
> > head:   551c722f40809618230001baccf219193e22fc5a
> > commit: d4dba3b9c03a326cfa73833d6b166aeb442f82b5 lib: decompress_bunzip2: fix 32-bit shift undefined behavior
> > date:   6 months ago
> > config: mips-randconfig-r2300-20260930 (https://download.01.org/0day-ci/archive/20260930/202609301826.MFaFMsmd-lkp@xxxxxxxxx/config)
> > compiler: mips-linux-gcc (GCC) 15.2.0
> > sparse: v0.6.5-rc1
> > reproduce (this is a W=1 build): (https://download.01.org/0day-ci/archive/20260930/202609301826.MFaFMsmd-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
> > | Fixes: d4dba3b9c03a ("lib: decompress_bunzip2: fix 32-bit shift undefined behavior")
> > | Reported-by: kernel test robot <lkp@xxxxxxxxx>
> > | Closes: https://lore.kernel.org/oe-kbuild-all/202609301826.MFaFMsmd-lkp@xxxxxxxxx/
> > 
> > All errors (new ones prefixed by >>):
> > 
> >    mips-linux-ld: arch/mips/boot/compressed/decompress.o: in function `get_bits':
> > >> arch/mips/boot/compressed/decompress.c:(.text+0xf4): undefined reference to `__ashldi3'
> > >> mips-linux-ld: arch/mips/boot/compressed/decompress.c:(.text+0x168): undefined reference to `__ashldi3'
> 
> I dunno, I'd be suspecting a toolchain issue here?
> 
> --- a/lib/decompress_bunzip2.c
> +++ b/lib/decompress_bunzip2.c
> @@ -135,7 +135,7 @@ static unsigned int INIT get_bits(struct bunzip_data *bd, char bits_wanted)
>  		}
>  		/* Avoid 32-bit overflow (dump bit buffer to top of output) */
>  		if (bd->inbufBitCount >= 24) {
> -			bits = bd->inbufBits&((1 << bd->inbufBitCount)-1);
> +			bits = bd->inbufBits & ((1ULL << bd->inbufBitCount) - 1);
>  			bits_wanted -= bd->inbufBitCount;
>  			bits <<= bits_wanted;
>  			bd->inbufBitCount = 0;
> @@ -146,7 +146,7 @@ static unsigned int INIT get_bits(struct bunzip_data *bd, char bits_wanted)
>  	}
>  	/* Calculate result */
>  	bd->inbufBitCount -= bits_wanted;
> -	bits |= (bd->inbufBits >> bd->inbufBitCount)&((1 << bits_wanted)-1);
> +	bits |= (bd->inbufBits >> bd->inbufBitCount) & ((1ULL << bits_wanted) - 1);
>  
>  	return bits;
>  }
> 
> 32-bit MIPS should be able to do this?

FWIW the patch seems entirely bogus. I don't think you can have inbufBitCount >=
32. If you could, then the patch would still not fix anything, because
bd->inbufBits is an (32-bit) unsigned int.

As per MIPS itself, MIPS does not link ashldi3.o into the decompressor for BZ2.
It only does so for XZ and ZSTD.

Changing arch/mips/boot/compressed/Makefile would work, but since the change is
entirely wrong I would suggest perhaps reverting?


-- 
Pedro