[ia64] objcopy and constant-gp

[ia64] objcopy and constant-gp

[Jakub Jermar]

Hi,

the following stopped working for me in ia64 binutils 2.18:

1. I have a binary file and want to objcopy it from the binary format to 
elf64-ia64-little, creating one ELF section in it, the result is called 
empty.o
2. I want to link empty.o with other .o files that were compiled with 
-mconstant-gp
3. ld returns an error complaining about linking constant-gp and 
non-constant-gp object files

So I would like to know if you consider this a regression or if it is 
actually a feature or a fix introduced in the newest version.

Anyway, what I am now most concerned about is if there is a 
straightforward way to specify that empty.o should be constructed with 
the constant-gp flag. (There is an easy workaround for this: after 
objcopy, patch the ELF file manually and set the constant-gp bit using 
some hex editor).

Please respond directly to my email address as I am not subscribed in 
this list.

Thanks,
Jakub

Re: [ia64] objcopy and constant-gp

[Nick Clifton]

Hi Jakub,

> 1. I have a binary file and want to objcopy it from the binary format to 
> elf64-ia64-little, creating one ELF section in it, the result is called 
> empty.o
> 2. I want to link empty.o with other .o files that were compiled with 
> -mconstant-gp
> 3. ld returns an error complaining about linking constant-gp and 
> non-constant-gp object files

> So I would like to know if you consider this a regression or if it is 
> actually a feature or a fix introduced in the newest version.

I think I would count this as a feature rather than a bug, purely because there 
is a better way of achieving what you want to do:

   1. Create a small assembler file that includes the binary file you are
      interested in:

       .section foo, "a", @progbits
       .incbin "the_binary_file"

   2. Assemble this file, and make sure that you include the -mconstant-gp
      option on the command line:

        ia64-linux-as -mconstant-gp foo.s -o foo.o

   3. Link in this new object file with the rest of your application.

Cheers
   Nick

Re: [ia64] objcopy and constant-gp

[Tristan Gingold]

On Nov 12, 2007, at 9:36 AM, Jakub Jermar wrote:
> the following stopped working for me in ia64 binutils 2.18:
>
> 1. I have a binary file and want to objcopy it from the binary  
> format to elf64-ia64-little, creating one ELF section in it, the  
> result is called empty.o
> 2. I want to link empty.o with other .o files that were compiled  
> with -mconstant-gp
> 3. ld returns an error complaining about linking constant-gp and  
> non-constant-gp object files
>
> So I would like to know if you consider this a regression or if it  
> is actually a feature or a fix introduced in the newest version.
>
> Anyway, what I am now most concerned about is if there is a  
> straightforward way to specify that empty.o should be constructed  
> with the constant-gp flag. (There is an easy workaround for this:  
> after objcopy, patch the ELF file manually and set the constant-gp  
> bit using some hex editor).

This behaviour sounds reasonable.

You'd better to create empty.s which .incbin (see gas manual) the  
binary file.  Then you assemble empty.s
using the right options (--mconstant-gp).
The link should be successful.

Tristan.

Re: [ia64] objcopy and constant-gp

[Jakub Jermar]

Hi Nick and Tristan,

Nick Clifton wrote:
>       .section foo, "a", @progbits
>       .incbin "the_binary_file"

this works. But it is rather an acceptable workaround.
Moreover, I need to use the same trick for different platforms and some 
platforms' assemblers use '%' instead of '@' (but that's managable).

I think that adding a flag to objcopy that would allow one to set file 
header flags will be a little bit better.

Anyway, thanks a lot!

Jakub

Re: [ia64] objcopy and constant-gp

[Nick Clifton]

Hi Jakub,

>>       .section foo, "a", @progbits
>>       .incbin "the_binary_file"
> 
> this works. But it is rather an acceptable workaround.

I think that you might mean "unacceptable" here... :-)

> Moreover, I need to use the same trick for different platforms and some 
> platforms' assemblers use '%' instead of '@' (but that's managable).

True.

> I think that adding a flag to objcopy that would allow one to set file 
> header flags will be a little bit better.

But very target specific if you want to use printable names for the flag bits. 
  Still it is a feature that might prove useful to other people, so if you want 
to implement it then please go ahead.

Cheers
   Nick

Re: [ia64] objcopy and constant-gp

[Jakub Jermar]

Nick Clifton wrote:
> Hi Jakub,
> 
>>>       .section foo, "a", @progbits
>>>       .incbin "the_binary_file"
>>
>> this works. But it is rather an acceptable workaround.
> 
> I think that you might mean "unacceptable" here... :-)

Acceptable was just right.
It did the job for me, but I'd do it differently if the tool supported it.

>> I think that adding a flag to objcopy that would allow one to set file 
>> header flags will be a little bit better.
> 
> But very target specific if you want to use printable names for the flag 
> bits.  Still it is a feature that might prove useful to other people, so 
> if you want to implement it then please go ahead.

Hm, then maybe hex values would do... Anyway, objdump and readelf can 
print those hex values in human-readable ways (eg. constant-gp). Sorry, 
I don't see myself implementing this anytime soon :-)

Regards,
Jakub

RE: [ia64] objcopy and constant-gp

[Dave Korn]

On 12 November 2007 16:19, Jakub Jermar wrote:

> Moreover, I need to use the same trick for different platforms 

  Are you sure?  Surely other platforms don't have "-mconstant-gp"?

    cheers,
      DaveK
-- 
Can't think of a witty .sigline today....

Re: [ia64] objcopy and constant-gp

[Jakub Jermar]

Hi,

Dave Korn wrote:
>> Moreover, I need to use the same trick for different platforms 
> 
>   Are you sure?  Surely other platforms don't have "-mconstant-gp"?

This is a misunderstanding. Other platforms don't have -mconstant-gp, 
but I need to link empty.o with HelenOS kernel on all other supported 
platforms. So I need a mechanism that is preferably universal and can be 
part of the main Makefile. (And I have found that mechanism thanks to 
the help I received here.)

Jakub