elf.sc and shared library for binutils

elf.sc and shared library for binutils

[H.J. Lu]

Here are some comments from elf.sc:

  /* Adjust the address for the data segment.  We want to adjust up to
     the same address within the page on the next page up.  It would
     be more correct to do this:
       ${RELOCATING+. = ${DATA_ADDR-ALIGN(${MAXPAGESIZE})
		+ ((ALIGN(8) + ${MAXPAGESIZE} - ALIGN(${MAXPAGESIZE}))
		   & (${MAXPAGESIZE} - 1)};}

I think the correct one should be

       ${RELOCATING+. = ALIGN(${MAXPAGESIZE})
		+ ((ALIGN(8) + ${MAXPAGESIZE} - ALIGN(${MAXPAGESIZE}))
		   & (${MAXPAGESIZE} - 1)};}

It should be independent of DATA_ADDR.

I have been adding the ELF shared library support for binutils under
Linux for a while. Any chance to support it in the official source?

H.J.

Re: elf.sc and shared library for binutils

[Eric Youngdale]

On Feb 25,  5:06pm, H.J. Lu wrote:
> Subject: elf.sc and shared library for binutils
> Here are some comments from elf.sc:
>
>   /* Adjust the address for the data segment.  We want to adjust up
to
>      the same address within the page on the next page up.  It
would
>      be more correct to do this:

	Maybe I am missing something, but why is this so important.
 All we
end up doing is wasting one page of VM (not physical memory, just
virtual memory).
Is there something else here?

-Eric


-- 
"The woods are lovely, dark and deep.  But I have promises to keep,
And lines to code before I sleep, And lines to code before I sleep."

Re: elf.sc and shared library for binutils

[Mike Meissner]

| On Feb 25,  5:06pm, H.J. Lu wrote:
| > Subject: elf.sc and shared library for binutils
| > Here are some comments from elf.sc:
| >
| >   /* Adjust the address for the data segment.  We want to adjust up
| to
| >      the same address within the page on the next page up.  It
| would
| >      be more correct to do this:
| 
| 	Maybe I am missing something, but why is this so important.
|  All we
| end up doing is wasting one page of VM (not physical memory, just
| virtual memory).
| Is there something else here?

If you don't do this, each program will be one physical page larger,
since the pages in the data area would start on a new page, leaving a
hole in the program file as it exists on disk between the text and
data.

This is why V.4 specifies this behavior.

-- 
Michael Meissner, Cygnus Support (East Coast)
Suite 105, 48 Grove Street, Somerville, MA 02144, USA
meissner@cygnus.com,	617-629-3016 (office),	617-629-3010 (fax)

Re: elf.sc and shared library for binutils

[Ian Lance Taylor]

   From: Mike Meissner <meissner@cygnus.com>
   Date: Mon, 27 Feb 1995 09:54:13 -0500

   If you don't do this, each program will be one physical page larger,
   since the pages in the data area would start on a new page, leaving a
   hole in the program file as it exists on disk between the text and
   data.

The linker already does this.  The issue at hand is more subtle.  It
is how to handle a program whose text segment ends precisely on a page
boundary.  Ideally the data segment should start on the next page,
immediately following the text segment.  Currently the linker will
skip a page, wasting a page of virtual memory address space.  Fixing
this is complex; see the comment in ld/scripttempl/elf.sc.

Ian

Re: elf.sc and shared library for binutils

[Ian Lance Taylor]

   From: hjl@nynexst.com (H.J. Lu)
   Date: Sat, 25 Feb 95 17:06:41 EST

   Here are some comments from elf.sc:

     /* Adjust the address for the data segment.  We want to adjust up to
	the same address within the page on the next page up.  It would
	be more correct to do this:
	  ${RELOCATING+. = ${DATA_ADDR-ALIGN(${MAXPAGESIZE})
		   + ((ALIGN(8) + ${MAXPAGESIZE} - ALIGN(${MAXPAGESIZE}))
		      & (${MAXPAGESIZE} - 1)};}

   I think the correct one should be

	  ${RELOCATING+. = ALIGN(${MAXPAGESIZE})
		   + ((ALIGN(8) + ${MAXPAGESIZE} - ALIGN(${MAXPAGESIZE}))
		      & (${MAXPAGESIZE} - 1)};}

   It should be independent of DATA_ADDR.

I believe that it should depend upon DATA_ADDR if it is set.  Note
that most targets do not set DATA_ADDR.  However, Irix 5 does set
DATA_ADDR.  On Irix 5, unlike most ELF targets, the .data section
always starts at 0x10000000.  I think the GNU linker may as well be
compatible.

In any case, since DATA_ADDR is not normally set, why bother to make
this change?

   I have been adding the ELF shared library support for binutils under
   Linux for a while. Any chance to support it in the official source?

Yes, I would think so.  I was not aware that there was any shared
library support that was not in the FSF sources.  What sort of stuff
is it?

Ian