_ebss == _edata if MMU

_ebss == _edata if MMU

[Geert Uytterhoeven]

On ARAnyM:

Virtual kernel memory layout:
    vector  : 0x002f4d10 - 0x002f5110   (   1 KiB)
    kmap    : 0xd0000000 - 0xf0000000   ( 512 MiB)
    vmalloc : 0x11800000 - 0xd0000000   (3048 MiB)
    lowmem  : 0x00000000 - 0x11000000   ( 272 MiB)
      .init : 0x00319000 - 0x0033c000   ( 140 KiB)
      .text : 0x00001000 - 0x002487b8   (2334 KiB)
      .data : 0x0024b540 - 0x00318a40   ( 822 KiB)
      .bss  : 0x002f4ae0 - 0x00318a40   ( 144 KiB)

End of data and end of bss are identical, as arch/m68k/kernel/vmlinux-std.lds
says bss is a subset of data:

  _sdata = .;                   /* Start of data section */

  RODATA

  RW_DATA_SECTION(16, PAGE_SIZE, THREAD_SIZE)

  _sbss = .;
  BSS_SECTION(0, 0, 0)
  _ebss = .;

  _edata = .;                   /* End of data section */

On !MMU, bss is not embedded in data.

Gr{oetje,eeting}s,

                        Geert

--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds

Re: _ebss == _edata if MMU

[Andreas Schwab]

Geert Uytterhoeven <geert@linux-m68k.org> writes:

> On ARAnyM:
>
> Virtual kernel memory layout:
>     vector  : 0x002f4d10 - 0x002f5110   (   1 KiB)
>     kmap    : 0xd0000000 - 0xf0000000   ( 512 MiB)
>     vmalloc : 0x11800000 - 0xd0000000   (3048 MiB)
>     lowmem  : 0x00000000 - 0x11000000   ( 272 MiB)
>       .init : 0x00319000 - 0x0033c000   ( 140 KiB)
>       .text : 0x00001000 - 0x002487b8   (2334 KiB)
>       .data : 0x0024b540 - 0x00318a40   ( 822 KiB)
>       .bss  : 0x002f4ae0 - 0x00318a40   ( 144 KiB)
>
> End of data and end of bss are identical, as arch/m68k/kernel/vmlinux-std.lds
> says bss is a subset of data:

It's just the _edata symbol, I don't think this is a problem.  After
all, bss is only zero-initialized data, thus still part of kernel data.

Andreas.

-- 
Andreas Schwab, schwab@linux-m68k.org
GPG Key fingerprint = 58CA 54C7 6D53 942B 1756  01D3 44D5 214B 8276 4ED5
"And now for something completely different."

Re: _ebss == _edata if MMU

[Greg Ungerer]

Hi Geert,

On 04/18/2012 05:55 PM, Geert Uytterhoeven wrote:
> On ARAnyM:
>
> Virtual kernel memory layout:
>      vector  : 0x002f4d10 - 0x002f5110   (   1 KiB)
>      kmap    : 0xd0000000 - 0xf0000000   ( 512 MiB)
>      vmalloc : 0x11800000 - 0xd0000000   (3048 MiB)
>      lowmem  : 0x00000000 - 0x11000000   ( 272 MiB)
>        .init : 0x00319000 - 0x0033c000   ( 140 KiB)
>        .text : 0x00001000 - 0x002487b8   (2334 KiB)
>        .data : 0x0024b540 - 0x00318a40   ( 822 KiB)
>        .bss  : 0x002f4ae0 - 0x00318a40   ( 144 KiB)
>
> End of data and end of bss are identical, as arch/m68k/kernel/vmlinux-std.lds
> says bss is a subset of data:
>
>    _sdata = .;                   /* Start of data section */
>
>    RODATA
>
>    RW_DATA_SECTION(16, PAGE_SIZE, THREAD_SIZE)
>
>    _sbss = .;
>    BSS_SECTION(0, 0, 0)
>    _ebss = .;
>
>    _edata = .;                   /* End of data section */
>
> On !MMU, bss is not embedded in data.

I noticed the same ending of .data and .bss when I put that memory
table print out code in :-)  I didn't want to change the linker
script just to make it seem more logical.

But now that you have bought it up... It seems a quick check of ARM
and x86 have _edata really at the end of the .data, and the .bss is
separate. Should we change it to be consistent with other arches?

Regards
Greg


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