Re: relocation of shared libs not based at 0

[Kevin Buettner <kevinb at redhat dot com>]

On Jan 8,  4:52pm, Kris Warkentin wrote:

> This works fine on QNX and (I assume) NetBSD so it looks rather like we just
> have a difference of opinion on how the shared object loader should fill
> things in.  We wanted to keep our linker's behaviour for some future
> enhancements (pre-relocating shared objects on flash memory, etc.) so I was
> hoping the fix below (Paul's code with some extra comments) might be
> acceptable.  That way Paul and I could just define LM_ADDR_IS_NOT_LOAD_BASE
> in our tm-<host>.h and we'd be off to the races.
> 
> static void
> svr4_relocate_section_addresses (struct so_list *so,
>                                  struct section_table *sec)
> {
> #if LM_ADDR_IS_NOT_LOAD_BASE
>   /* On some platforms, (ie. QNX, NetBSD) LM_ADDR is the assigned
>      address, not the offset.
>      The addresses are formed as follows:
>      LM_ADDR is the target address where the shared library file
>      is mapped, so the actual section start address is LM_ADDR plus
>      the section offset within the shared library file.  The end
>      address is that plus the section length.  Note that we pay no
>      attention to the section start address as recorded in the
>      library header.
>   */
>    sec->endaddr = svr4_truncate_ptr (sec->endaddr - sec->addr +
>       sec->the_bfd_section->filepos +
>       LM_ADDR (so));
>    sec->addr    = svr4_truncate_ptr (sec->the_bfd_section->filepos +
>       LM_ADDR (so));
> #else
>   sec->addr    = svr4_truncate_ptr (sec->addr    + LM_ADDR (so));
>   sec->endaddr = svr4_truncate_ptr (sec->endaddr + LM_ADDR (so));
> #endif
> }

The problem that I have with the above is that it's not possible to
build a cross debugger that'll have shared library support for both
Linux and NetBSD.

If we could somehow detect (perhaps via the osabi mechanism) that we
have one of the lm-addr-is-not-load-base platforms and enable that
code at runtime, I wouldn't mind...

Kevin