[Linux-ia64] IA64 ELF header question...

[Linux-ia64] IA64 ELF header question...

[Peter Bergner]

Does anyone know whether the e_entry field in the IA64 ELF header
is equal to the address of the function descriptor of the _start
routine or whether it's equal to the address of the _start code?
(ie, ._start)  Looking at the IA64 kernel and GLIBC sources
(the IA64 ABI was a little vague), I'm guessing e_entry is actually
the address of the _start code (ie, e_entry = address of ._start).

The reason I ask, is that I'm working on the PPC64 GLIBC port
and our ABI states that our e_entry field is equal to the
address of the function descriptor for _start.  This was fine
for statically linked apps.  All we needed to change in the
kernel was an extra dereference in start_thread to load the
actual code address of _start and away we went.

My problem is with dynamically linked apps.  The kernel is smart
enough to know when it loads ld.so to reloc the e_entry field.
The problem is that the function descriptor entries for _start
need to be reloc'd too before we can use them.  I'd prefer not
to touch arch independent code to fix this, but it doesn't look
like I have enough info in start_thread to determine whether
I need to reloc the function descriptor entries or not before
using them.  Since PPC64 and IA64 share the use of function
descriptors, I thought I'd check with people here on how this
was solved for IA64.  Anyone have any ideas I can use?

...I guess another option I could try is to change the PowerPC64-ELF
ABI to say that the e_entry field holds the address of ._start
rather than _start.  Although, I'm not sure whether that's possible
or not.


Peter

--
Peter Bergner
SLIC Optimizing Translator Development / Linux PPC64 Kernel Development
IBM Rochester, MN
bergner@vnet.ibm.com

Re: [Linux-ia64] IA64 ELF header question...

[Cary Coutant]

>Since PPC64 and IA64 share the use of function
>descriptors, I thought I'd check with people here on how this
>was solved for IA64.  Anyone have any ideas I can use?

PA-RISC also uses function descriptors. On HP-UX, for both PA-RISC and 
IA-64, the e_entry field is the address of the code entry point itself, 
rather than the address of a function descriptor. Our dynamic loader 
initializes its own gp value, and when it's time for the dynamic loader 
to call the application's entry point, it knows what the gp value should 
be, so we don't need a function descriptor.


Cary Coutant
HP-UX Runtime Architect

Re: [Linux-ia64] IA64 ELF header question...

[Peter Bergner]

Cary Coutant wrote:
> PA-RISC also uses function descriptors. On HP-UX, for both PA-RISC and
> IA-64, the e_entry field is the address of the code entry point itself,
> rather than the address of a function descriptor. Our dynamic loader
> initializes its own gp value, and when it's time for the dynamic loader
> to call the application's entry point, it knows what the gp value should
> be, so we don't need a function descriptor.

This looks also to be the case for Linux/IA64 (from what I gathered from
looking at the IA64 kernel and GLIBC source).  Changing our ABI to match
this doesn't look promising, as we're not the only OS using this ABI.
This means I'll need to modify the kernel to reloc our function
descriptor (FD)
entries.  The only problem is, I don't have enough information in
start_thread
to know whether I need to reloc the FD entries or not.  Seems like I'll
need
to place some code in fs/binfmt_elf.c to gather up the information
needed
to perform the reloc's in start_thread.

Note I don't really want to reloc the function descriptor entries, just
the values I copy out of the entries as I stuff them into my pt_regs
struct.

Peter