Re: [BUG mips llvm] MIPS: malformed R_MIPS_{HI16,LO16} with LLVM

From: Nick Desaulniers <ndesaulniers@google.com>
Date: Tue, 12 Jan 2021 14:14:58 -0800

On Mon, Jan 11, 2021 at 12:50 PM Alexander Lobakin [off-list ref] wrote:

quoted

quoted

The disassembly for me produces:
    399c: 3c 03 00 00   lui     $3, 0 <phy_device_free>
                        0000399c:  R_MIPS_HI16  .text
...
    39a8: 24 63 3a 5c   addiu   $3, $3, 14940 <phy_probe>
                        000039a8:  R_MIPS_LO16  .text

So, in your case the values of the instructions that relocs refer are:

0x3c030000 R_MIPS_HI16
0x24633a5c R_MIPS_LO16

Mine were:

0x3c010000
0x24339444

Your second one doesn't have bit 15 set, so I think this pair won't
break the code.
Try to hunt for R_MIPS_LO16 that have this bit set, i.e. they have
'8', '9', 'a', 'b', 'c', 'd' or 'e' as their [15:12].

I don't think any of my R_MIPS_LO16 in that file have that bit set.
See attached.

Well, seems like you got lucky here.
You can try to check for other modules if any of them have
R_MIPS_LO16 with bit 15 set.

Also, you can try to enable:
CONFIG_LD_DEAD_CODE_DATA_ELIMINATION=y
CONFIG_TRIM_UNUSED_KSYMS=y

to alter the build process. These options didn't change anything
in terms of relocs for me though.

--
Thanks,
~Nick Desaulniers

Thanks,
Al