Re: Questions about the LMA and VMA in a linker script

[Yubin Ruan]

On 2016年07月16日 02:42, Dave Hylands wrote:
>
> On Thu, Jul 14, 2016 at 1:45 AM, Yubin Ruan  > wrote:
>
> On Wed, Jul 13, 2016 at 7:33 PM, Yubin Ruan
> mailto:ablacktsh...@gmail.com>
> >>
> wrote:
>
>  Hi,
>  I got some question about the AT directive in linker
> script. I have
>  post this question to binutils{at}sourceware.org
> 
>   with no reply.
>
>  Hopefully someone can help me out.
>
>  After some searching and asking, I finally know that the AT
> directive
>  tell the linker about LMA of  a section.
>
>  For example there is some linker script like this:
>
>   SECTIONS
>   {
>   . = 0X8010;
>   .text : AT(0x10) {
>   *(.text .stub .text.* .gnu.linkonce.t.*)
>   }
>
> ... blah blah ...
>   }
>
>  Now 0x801 is a VMA, and 0x10 is a LMA.
>
>  My question is, is LMA the same as the physical address in
> a ELF
>  program header ? A typical ELF declaration would be
> something like
>  this:
>
>  typedef struct
>  {
> Elf32_Wordp_type; /* Segment type */
> Elf32_Off p_offset;   /* Segment file
> offset */
> Elf32_Addrp_vaddr;/* Segment virtual
> address */
> Elf32_Addrp_paddr;/* Segment
> physical address */
> Elf32_Wordp_filesz;   /* Segment size in
> file */
> Elf32_Wordp_memsz;/* Segment size in
> memory */
> Elf32_Wordp_flags;/* Segment flags */
> Elf32_Wordp_align;/* Segment
> alignment */
>  } Elf32_Phdr;
>
>  Is LMA just **p_paddr** in the program header?
>
> ...snip...
>
> Thank you for replying. I think I understand what you mean.
> But I still want the answer to my question, that is, is LMA just
> **p_paddr** in the program header?
>
>
> I'm pretty sure that's the case. There are actually 2 sets of headers.
> You can use:
>
> objdump -p foo.elf
>
> to view the "private" headers which shows you the p_vaddr and p_paddr
> fields.
>
> And you can use
>
> objdump -h foo.elf
>
> to view the section headers.
>
> Here's some example output for a typical embedded program:
>
> 2216 >objdump -p firmware.elf
>
> firmware.elf: file format elf32-little
>
> Program Header:
>  LOAD off0x8000 vaddr 0x0800 paddr 0x0800 align 2**15
>   filesz 0x288c memsz 0x288c flags r-x
>  LOAD off0x0001 vaddr 0x0802 paddr 0x0802 align 2**15
>   filesz 0x00040470 memsz 0x00040470 flags r-x
>  LOAD off0x00058000 vaddr 0x2000 paddr 0x08060470 align 2**15
>   filesz 0x0108 memsz 0x64f0 flags rw-
>  LOAD off0x0005e4f0 vaddr 0x200064f0 paddr 0x08060578 align 2**15
>   filesz 0x memsz 0x4000 flags rw-
>  LOAD off0x0005a4f0 vaddr 0x2000a4f0 paddr 0x08060578 align 2**15
>   filesz 0x memsz 0x0800 flags rw-
>
> 2217 >objdump -h firmware.elf
>
> firmware.elf: file format elf32-little
>
> Sections:
> Idx Name  Size  VMA   LMA   File off  Algn
>0 .isr_vector   288c  0800  0800  8000  2**2
>CONTENTS, ALLOC, LOAD, READONLY, CODE
>1 .text 00040470  0802  0802  0001  2**2
>CONTENTS, ALLOC, LOAD, READONLY, CODE
>2 .data 0108  2000  08060470  00058000  2**2
>CONTENTS, ALLOC, LOAD, DATA
>3 .bss  63e8  2108  08060578  00058108  2**2
>ALLOC
>4 .heap 4000  200064f0  08060578  0005e4f0  2**0
>ALLOC
>5 .stack0800  2000a4f0  08060578  0005a4f0  2**0
>ALLOC
>6 .ARM.attributes 0037      00058108  2**0
>CONTENTS, READONLY
>7 .comment  00e0      0005813f  2**0
>CONTENTS, READONLY
>
> --
> Dave Hylands
> Shuswap, BC, Canada
> http://www.davehylands.com

Thanks :-)
Your reply really eliminate my doubts.

Regards,
Ruan.


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Re: Questions about the LMA and VMA in a linker script

[Dave Hylands]

On Thu, Jul 14, 2016 at 1:45 AM, Yubin Ruan  wrote:

> On Wed, Jul 13, 2016 at 7:33 PM, Yubin Ruan > > wrote:
>>
>> Hi,
>> I got some question about the AT directive in linker script. I have
>> post this question to binutils{at}sourceware.org
>>  with no reply.
>>
>> Hopefully someone can help me out.
>>
>> After some searching and asking, I finally know that the AT directive
>> tell the linker about LMA of  a section.
>>
>> For example there is some linker script like this:
>>
>>  SECTIONS
>>  {
>>  . = 0X8010;
>>  .text : AT(0x10) {
>>  *(.text .stub .text.* .gnu.linkonce.t.*)
>>  }
>>
>>... blah blah ...
>>  }
>>
>> Now 0x801 is a VMA, and 0x10 is a LMA.
>>
>> My question is, is LMA the same as the physical address in a ELF
>> program header ? A typical ELF declaration would be something like
>> this:
>>
>> typedef struct
>> {
>>Elf32_Wordp_type; /* Segment type */
>>Elf32_Off p_offset;   /* Segment file offset */
>>Elf32_Addrp_vaddr;/* Segment virtual address */
>>Elf32_Addrp_paddr;/* Segment physical address
>> */
>>Elf32_Wordp_filesz;   /* Segment size in file */
>>Elf32_Wordp_memsz;/* Segment size in memory */
>>Elf32_Wordp_flags;/* Segment flags */
>>Elf32_Wordp_align;/* Segment alignment */
>> } Elf32_Phdr;
>>
>> Is LMA just **p_paddr** in the program header?
>>
>> ...snip...

> Thank you for replying. I think I understand what you mean.
> But I still want the answer to my question, that is, is LMA just
> **p_paddr** in the program header?
>

I'm pretty sure that's the case. There are actually 2 sets of headers. You
can use:

objdump -p foo.elf

to view the "private" headers which shows you the p_vaddr and p_paddr
fields.

And you can use

objdump -h foo.elf

to view the section headers.

Here's some example output for a typical embedded program:

2216 >objdump -p firmware.elf

firmware.elf: file format elf32-little

Program Header:
LOAD off0x8000 vaddr 0x0800 paddr 0x0800 align 2**15
 filesz 0x288c memsz 0x288c flags r-x
LOAD off0x0001 vaddr 0x0802 paddr 0x0802 align 2**15
 filesz 0x00040470 memsz 0x00040470 flags r-x
LOAD off0x00058000 vaddr 0x2000 paddr 0x08060470 align 2**15
 filesz 0x0108 memsz 0x64f0 flags rw-
LOAD off0x0005e4f0 vaddr 0x200064f0 paddr 0x08060578 align 2**15
 filesz 0x memsz 0x4000 flags rw-
LOAD off0x0005a4f0 vaddr 0x2000a4f0 paddr 0x08060578 align 2**15
 filesz 0x memsz 0x0800 flags rw-

2217 >objdump -h firmware.elf

firmware.elf: file format elf32-little

Sections:
Idx Name  Size  VMA   LMA   File off  Algn
  0 .isr_vector   288c  0800  0800  8000  2**2
  CONTENTS, ALLOC, LOAD, READONLY, CODE
  1 .text 00040470  0802  0802  0001  2**2
  CONTENTS, ALLOC, LOAD, READONLY, CODE
  2 .data 0108  2000  08060470  00058000  2**2
  CONTENTS, ALLOC, LOAD, DATA
  3 .bss  63e8  2108  08060578  00058108  2**2
  ALLOC
  4 .heap 4000  200064f0  08060578  0005e4f0  2**0
  ALLOC
  5 .stack0800  2000a4f0  08060578  0005a4f0  2**0
  ALLOC
  6 .ARM.attributes 0037      00058108  2**0
  CONTENTS, READONLY
  7 .comment  00e0      0005813f  2**0
  CONTENTS, READONLY

-- 
Dave Hylands
Shuswap, BC, Canada
http://www.davehylands.com
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Re: Questions about the LMA and VMA in a linker script

[Yubin Ruan]

> On Wed, Jul 13, 2016 at 7:33 PM, Yubin Ruan  > wrote:
>
> Hi,
> I got some question about the AT directive in linker script. I have
> post this question to binutils{at}sourceware.org
>  with no reply.
> Hopefully someone can help me out.
>
> After some searching and asking, I finally know that the AT directive
> tell the linker about LMA of  a section.
>
> For example there is some linker script like this:
>
>  SECTIONS
>  {
>  . = 0X8010;
>  .text : AT(0x10) {
>  *(.text .stub .text.* .gnu.linkonce.t.*)
>  }
>
>... blah blah ...
>  }
>
> Now 0x801 is a VMA, and 0x10 is a LMA.
>
> My question is, is LMA the same as the physical address in a ELF
> program header ? A typical ELF declaration would be something like
> this:
>
> typedef struct
> {
>Elf32_Wordp_type; /* Segment type */
>Elf32_Off p_offset;   /* Segment file offset */
>Elf32_Addrp_vaddr;/* Segment virtual address */
>Elf32_Addrp_paddr;/* Segment physical address */
>Elf32_Wordp_filesz;   /* Segment size in file */
>Elf32_Wordp_memsz;/* Segment size in memory */
>Elf32_Wordp_flags;/* Segment flags */
>Elf32_Wordp_align;/* Segment alignment */
> } Elf32_Phdr;
>
> Is LMA just **p_paddr** in the 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.
>
> On 2016, July 14, at 14:07, Dave Hylands wrote:
> Replying to all this time.
>
> Currently, I'm most recently familiar with small non-MMU processors (not
> running linux), and in that case, the VMA is the final address
> (typically in RAM) that the section will be loaded to.
> The LMA is the address (typically in ROM) that the section will be at
> when the program starts execution.
>
> A typical example of this is initialized data. In the image, this
> "initialized data" section will be stored in ROM and copied to RAM by
> the C runtime library before calling main.
>
> In the linux kernel, the kernel image will be linked against its final
> virtual address (the VMA) and the LMA would correspond to the physical
> address that the kernel will be loaded at (since the MMU is typically
> off when the kernel image is loaded).
>
> There are lots of variations and reasons why things might not be exactly
> like I described (different architectures have different conventions),
> but that's the jist of things.
>
>
>
>
> --
> Dave Hylands
> Shuswap, BC, Canada
> http://www.davehylands.com

Thank you for replying. I think I understand what you mean.
But I still want the answer to my question, that is, is LMA just 
**p_paddr** in the program header?

Regards,
Ruan

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Re: Questions about the LMA and VMA in a linker script

[Dave Hylands]

Replying to all this time.

Currently, I'm most recently familiar with small non-MMU processors (not
running linux), and in that case, the VMA is the final address (typically
in RAM) that the section will be loaded to.
The LMA is the address (typically in ROM) that the section will be at when
the program starts execution.

A typical example of this is initialized data. In the image, this
"initialized data" section will be stored in ROM and copied to RAM by the C
runtime library before calling main.

In the linux kernel, the kernel image will be linked against its final
virtual address (the VMA) and the LMA would correspond to the physical
address that the kernel will be loaded at (since the MMU is typically off
when the kernel image is loaded).

There are lots of variations and reasons why things might not be exactly
like I described (different architectures have different conventions), but
that's the jist of things.

On Wed, Jul 13, 2016 at 7:33 PM, walker lala  wrote:

> Hi,
> I got some question about the AT directive in linker script. I have
> post this question to binutils{at}sourceware.org with no reply.
> Hopefully someone can help me out.
>
> After some searching and asking, I finally know that the AT directive
> tell the linker about LMA of  a section.
>
> For example there is some linker script like this:
>
> SECTIONS
> {
> . = 0X8010;
> .text : AT(0x10) {
> *(.text .stub .text.* .gnu.linkonce.t.*)
> }
>
>   ... blah blah ...
> }
>
> Now 0x801 is a VMA, and 0x10 is a LMA.
>
> My question is, is LMA the same as the physical address in a ELF
> program header ? A typical ELF declaration would be something like
> this:
>
> typedef struct
> {
>   Elf32_Wordp_type; /* Segment type */
>   Elf32_Off p_offset;   /* Segment file offset */
>   Elf32_Addrp_vaddr;/* Segment virtual address */
>   Elf32_Addrp_paddr;/* Segment physical address */
>   Elf32_Wordp_filesz;   /* Segment size in file */
>   Elf32_Wordp_memsz;/* Segment size in memory */
>   Elf32_Wordp_flags;/* Segment flags */
>   Elf32_Wordp_align;/* Segment alignment */
> } Elf32_Phdr;
>
> Is LMA just **p_paddr** in the 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.
>
> ___
> Kernelnewbies mailing list
> Kernelnewbies@kernelnewbies.org
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>



-- 
Dave Hylands
Shuswap, BC, Canada
http://www.davehylands.com
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Questions about the LMA and VMA in a linker script

[walker lala]

Hi,
I got some question about the AT directive in linker script. I have
post this question to binutils{at}sourceware.org with no reply.
Hopefully someone can help me out.

After some searching and asking, I finally know that the AT directive
tell the linker about LMA of  a section.

For example there is some linker script like this:

SECTIONS
{
. = 0X8010;
.text : AT(0x10) {
*(.text .stub .text.* .gnu.linkonce.t.*)
}

  ... blah blah ...
}

Now 0x801 is a VMA, and 0x10 is a LMA.

My question is, is LMA the same as the physical address in a ELF
program header ? A typical ELF declaration would be something like
this:

typedef struct
{
  Elf32_Wordp_type; /* Segment type */
  Elf32_Off p_offset;   /* Segment file offset */
  Elf32_Addrp_vaddr;/* Segment virtual address */
  Elf32_Addrp_paddr;/* Segment physical address */
  Elf32_Wordp_filesz;   /* Segment size in file */
  Elf32_Wordp_memsz;/* Segment size in memory */
  Elf32_Wordp_flags;/* Segment flags */
  Elf32_Wordp_align;/* Segment alignment */
} Elf32_Phdr;

Is LMA just **p_paddr** in the 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.

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