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

[Nick Clifton <nickc@redhat.com>]

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.

Cheers
   Nick