Re: Error: attempt to get value of unresolved symbol `L0'

[Richard Biener <richard.guenther@gmail.com>]

On Tue, Oct 11, 2022 at 12:37 PM Nick Clifton <nickc@redhat.com> wrote:
>
> Hi Pali, Hi Richard,
>
> > Interesting... Another test case which is working fine:
> >
> >    kernoffs:
> >    .word 0x40000 - (. - 0x0)
>
> This works because this expression can be converted into an instruction
> and a relocation in the object file:
>
>    % as t.s -o t.o
>    % objdump -dr t.o
>    Disassembly of section .text:
>
>    00000000 <kernoffs>:
>     0:  0003fffc        .word   0x0003fffc
>                         0: R_ARM_REL32  *ABS*
>
> Which shows that when this object file is linked the word at offset 0
> inside the .text section should be converted into an absolute value of
> (pc - 0x4000), where pc is the address of the word.
>
> This instruction however:
>
>         .word - (. - 0x80008000)
>
> Cannot be converted since the linker would need to compute ((pc - 0x800800) * -1)
> which cannot be expressed by a single relocation.  Similarly:
>
>         .word KERNEL_OFFSET - (. - CONFIG_SYS_TEXT_BASE)
>
> Cannot be expressed by a single value, modified by a single relocation, even
> when the KERNEL_OFFSET and CONFIG_SYS_TEXT_BASE values are known at assembly
> time.
>
> A clever assembler might be able to rearrange the expression, assuming that
> overflow is unimportant, but gas does not do that.  But just for reference
> the following would work:
>
>         .word KERNEL_OFFSET + CONFIG_SYS_TEXT_BASE - .
>
>
> I agree however that this message:
>
>          t.s: Error: attempt to get value of unresolved symbol `L0'
>
> is unhelpful.  So I am going to check in a patch to change it to:
>
>         t.s: Error: expression is too complex to be resolved
>
> I looked into providing a file name and line number with the error
> message, but this would involve reworking a lot of the assembler's
> internal expression parser.

GCC has a global input_location conveniently available when all other
bets are off.  Maybe mention "relocation" in the error message somehow?
So "expression is too complex to be resolved by a single relocation"?

Richard.

>
> Cheers
>    Nick
>