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-...

Regards, Hao Lee