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Re: Executable memory: some apps that work on RH9 don't on FC1



> OK, so this is the piece that I'm missing.  Where can I learn more
> about these header entries?  I don't see anything in the libc
> reference about this, even though PT_LOAD is defined by libc.

libc provides elf.h, yes.  The details are part of the ELF spec, available
online from e.g. http://www.sco.com/developers/gabi/.  Looking at the phdr
entries in programs with readelf -l or objdump -p, their meaning is
probably obvious.  What you are probably interested in is how to control
their generation by the linker.  You will need to provide your own variant
of the normal built-in link script used to link an executable, that uses
the PHDRS directive explicitly lay out sections.  Here is the usual script
from `ld --verbose' for i386-*-linux-gnu hacked to add a leading load
segment at 0 for the ".reserved" section.  You'll have to give the linker
an input section of that name, e.g. with:

	.section ".reserved","a",@nobits
	.space 0x4000000
	.previous

to set the size of the output segment.


OUTPUT_FORMAT("elf32-i386", "elf32-i386",
	      "elf32-i386")
OUTPUT_ARCH(i386)
ENTRY(_start)
SEARCH_DIR("/usr/local/i686-pc-linux-gnu/lib"); SEARCH_DIR("/usr/local/lib"); SEARCH_DIR("/lib"); SEARCH_DIR("/usr/lib");
/* Do we need any of these for elf?
   __DYNAMIC = 0;    */

PHDRS
{
  headers PT_PHDR PHDRS ;
  interp PT_INTERP ;
  reserved PT_LOAD FLAGS(0) ;
  text PT_LOAD FILEHDR PHDRS ;
  data PT_LOAD ;
  dynamic PT_DYNAMIC ;
}

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