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Index > Linux > Extrn, segments and sections

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jorido



Joined: 23 Jan 2017
Posts: 53
jorido 12 Feb 2017, 04:17
Do I understand correctly this rule for Linux x86-64:

1) Either I can use this:


Code:

  format elf64 executable 3

  segment writeable
  ;.........

  segment executable

  start:
    ;..............
    



2) Or this:

Code:
  format elf64

  section '.data' writeable
  ;.........
  extrn some_external_c_function

  section '.text'  executable

  start:
    ;..............

    



That is:
a. "extrn" can't be used with "format elf64 executable 3"

b. for "format elf64 executable 3" only "segment" can be used, not "section"



If so, why is that?
Post 12 Feb 2017, 04:17
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system error



Joined: 01 Sep 2013
Posts: 670
system error 12 Feb 2017, 05:43
LOL

"elf64 executable 3" dynamic setup (import, segment etc) is to generate executable file directly. No intermediary .o file. Commonly used in these steps:

(compile) ----------------------------> RUN


"elf64" static setup (extrn, section etc) is to generate object files to be linked with anything later on. Produce .o file. Commonly used in these 3-step like:

(compile) --------> linking (gcc, ld, golink, link, alink) ---------> RUN

In general, you cannot use dynamic setup to create a static source and vice versa. You're not paying attention to your own previous threads.
Post 12 Feb 2017, 05:43
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jorido



Joined: 23 Jan 2017
Posts: 53
jorido 12 Feb 2017, 11:23
SOL

There're 2 yes-no questions. You're not paying attention.

ROL
Post 12 Feb 2017, 11:23
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system error



Joined: 01 Sep 2013
Posts: 670
system error 12 Feb 2017, 11:46
@jorido

You better just stick to your HTML 5.0 For Dummy book. Easier read.
FASM dynamic linking is just too much for some people.
Post 12 Feb 2017, 11:46
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jorido



Joined: 23 Jan 2017
Posts: 53
jorido 13 Feb 2017, 05:31
Have you read it? Would you recommend?
Post 13 Feb 2017, 05:31
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revolution
When all else fails, read the source


Joined: 24 Aug 2004
Posts: 20363
Location: In your JS exploiting you and your system
revolution 15 Feb 2017, 00:49
a. You can't link to an external symbol with extrn if you are not linking (format executable).

b. See your previous thread about section and segments.
Post 15 Feb 2017, 00:49
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