On Thu, Apr 05, 2018 at 11:25:23AM +0800, Hao Lee wrote:
> Hi,
>
> I'm confused about the location counter, especially when setting it to
> a new value in the output section.
>
> I write a simple program and a linker script to make my question more
> clear. The code is as follows:
>
> -----test.s---------
> section .text
> .globl _start
> _start:
> movq $1, %rax
> movq $0, %rbx
> int $0x80
>
> ------test.lds------
> SECTIONS
> {
> . = 0x10;
> label_1 = .;
> custom_section : {
> . = 0x20;
> label_2 = . ;
> label_3 = ABSOLUTE(.) ;
> *(.text) ;
> }
> }
>
> After linking, use nm command to print symbol addresses:
>
> 0000000000000010 T label_1
> 0000000000000030 T label_2
> 0000000000000030 A label_3
> 0000000000000030 T _start
>
> I can't understand why lable_2 is 0x30. As the LD documentation
> says[1], if '.' is used inside a section description, it refers to the
> byte offset from the start of that section, not an absolute address.
> In the custom_section, '.' is set to 0x20 which is a relative offset,
So it is relative, and 0x10 + 0x20 = 0x30 .
What is the problem?
Yubin
> so I think label_2 should also be 0x20. The value of label_3 is
> reasonable because it's an absolute address.
>
> Could someone please explain why label_2 is 0x30? Thanks!
>
>
> [1] https://sourceware.org/binutils/docs-2.30/ld/Location-Counter.html#Location-Counter
>
> Regards,
> Hao Lee
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