[Bug target/81863] [7 regression] -mword-relocations is unreliable

["arnd at linaro dot org" <gcc-bugzilla at gcc dot gnu dot org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=81863

--- Comment #7 from Arnd Bergmann <arnd at linaro dot org> ---
Created attachment 42009
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=42009&action=edit
preprocessed net/rds/recv.i

(In reply to ard.biesheuvel from comment #6)
> FWIW, the following makes the issue go away (tested on 4.9.4)
> 
> @@ -6196,7 +6210,9 @@
>    [(set (match_operand:SI 0 "nonimmediate_operand" "=r")
>  	(lo_sum:SI (match_operand:SI 1 "nonimmediate_operand" "0")
>  		   (match_operand:SI 2 "general_operand"      "i")))]
> -  "arm_arch_thumb2 && arm_valid_symbolic_address_p (operands[2])"
> +  "arm_arch_thumb2 && arm_valid_symbolic_address_p (operands[2])
> +   && (   GET_CODE (operands[2]) != SYMBOL_REF
> +       || !target_word_relocations)"
>    "movt%?\t%0, #:upper16:%c2"
>    [(set_attr "predicable" "yes")
>     (set_attr "predicable_short_it" "no")
> 
> I have no idea whether this is a suitable fix: I will leave that to the
> experts. Just providing this as a data point.

I tried this change and it apparently addressed one such problem on gcc-7.1.1
(in multiple kernel configurations):

/home/arnd/cross-gcc/bin/arm-linux-gnueabi-ld: drivers/mfd/janz-cmodio.o:
relocation R_ARM_THM_MOVW_ABS_NC against `a local symbol' can not be used when
making a shared object; recompile with -fPIC

but not another one:

/home/arnd/cross-gcc/bin/arm-linux-gnueabi-ld: net/rds/recv.o: relocation
R_ARM_MOVW_ABS_NC against `rds_stats' can not be used when making a shared
object; recompile with -fPIC

The first only showed up in configurations using -mthumb, while the second only
appeared only once so far, in a configuration using -marm. Attaching the
preprocessed source file, build with "arm-linux-gnueabi-gcc-7.1.1
-mword-relocations -march=armv7-a  -O1 -c recv.i"