Re: what does AT do in a linker scripts ?

[Yubin Ruan <ablacktshirt at gmail dot com>]

On 2016年07月13日 16:49, Erik Christiansen wrote:
> On 13.07.16 16:16, Yubin Ruan wrote:
> > Hi,
> > I am reading some C code and some linker scripts for `ld`.
> > I find something really hard to understand:
> >
> >      .text : AT(0x100000) {
> >          *(.text .stub .text.* .gnu.linkonce.t.*)
> >      }
> >
> > I understand what the `.text` and the wild char * do, but what does
> > the `AT` after the colon do ?
> > Need help.
>
> It specifies the LMA, i.e. the address at which the output section is to
> be loaded, e.g. into ROM. (As opposed to the VMA, the address at which
> the output section has been linked/located to run.)
>
> > And also, why is there no man page describing the syntax of linker scripts ?
>
> That is annoying, and has been for a very long time, but we need to use
> the documentation provided:
>
> # apt-get install binutils-doc
> $ info ld
>
> It's described in section: "3.6.8.2 Output Section LMA"
>
> Erik
Thanks for replying. Those infos you provided are really helpful.

May I ask another related question:

There are some linker script like this:

    SECTIONS
    {
        . = 0X80100000;
        .text : AT(0x100000) {
            *(.text .stub .text.* .gnu.linkonce.t.*)
        }

      ... blah blah ...
    }

Now 0x8010000 is a VMA, and 0x100000 is a LMA.
Can I treat the LMA the same as the physical address in a ELF program 
header ? A typical ELF declaration would be something like this:

typedef struct
{
  Elf32_Word    p_type;                 /* Segment type */
  Elf32_Off     p_offset;               /* Segment file offset */
  Elf32_Addr    p_vaddr;                /* Segment virtual address */
  Elf32_Addr    p_paddr;                /* Segment physical address */
  Elf32_Word    p_filesz;               /* Segment size in file */
  Elf32_Word    p_memsz;                /* Segment size in memory */
  Elf32_Word    p_flags;                /* Segment flags */
  Elf32_Word    p_align;                /* Segment alignment */
} Elf32_Phdr;

Is LMA just **p_paddr** in a program header?
My understanding is, when the linker link all the object files together 
and then output a executable file of ELF format, those LMA declare in 
the linker script would be the **p_paddr** in the executable file, so 
the loader can correspondingly put that program on the physical address 
as declared by **p_paddr**. Is that correct? Please correct me if you 
may. I'm reading some low level code and is not really familiar with 
those low level stuff.

Thanks in advance!
Ruan.