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Need -un-initialized memory allocation

Chris Demetriou cgd@google.com
Fri Jul 4 07:36:00 GMT 2008 
[Sorry for the dup, Anton.  Meant to reply to the list, but failed the
first time.]

On Thu, Jul 3, 2008 at 13:48, Anton Tichawa <anton.tichawa@chello.at> wrote:
> I looked for a directive that allocates uninitialized memory, but didn't
> find any. What I want is something like
>
> Symbol1:    <reserve 0x10000 longwords>
> Symbol2:    <reserve 200 bytes>
> ...
>
> So the only effect would be the definition of the symbols.
>

If definition of the symbols is truly the only effect that you want (i.e.,
you don't care about changing the value of '.' -- not clear from your
description where you that you want to "reserve" space), then your solution
may simply be ".set".

For instance:

$ cat x.s
    .set symbol1, .
    .set symbol2, symbol1 + 0x1234567
    .set symbol3, symbol2 + 0x1234567
$ as x.s
$ objdump -xd a.out

a.out:     file format elf32-i386
a.out
architecture: i386, flags 0x00000010:
HAS_SYMS
start address 0x00000000

Sections:
Idx Name          Size      VMA       LMA       File off  Algn
  0 .text         00000000  00000000  00000000  00000034  2**2
                  CONTENTS, ALLOC, LOAD, READONLY, CODE
  1 .data         00000000  00000000  00000000  00000034  2**2
                  CONTENTS, ALLOC, LOAD, DATA
  2 .bss          00000000  00000000  00000000  00000034  2**2
                  ALLOC
SYMBOL TABLE:
00000000 l    d  .text  00000000 .text
00000000 l    d  .data  00000000 .data
00000000 l    d  .bss   00000000 .bss
00000000 l       .text  00000000 symbol1
01234567 l       .text  00000000 symbol2
02468ace l       .text  00000000 symbol3

("=" works similarly, e.g. code like "symbol2 = symbol1 + 0x1234567".)
That's just an example to show expressions, you can also use absolute
addresses, etc.

http://sourceware.org/binutils/docs-2.18/as/Set.html#Set

There are several similar directives that might be useful to you as well,
e.g. .equiv and .eqv.


chris
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