ELF instruction for section and branch.

Gagneet Singh gagneet@acmet.com
Fri Dec 19 15:49:00 GMT 2003


Hi!

Thanx for the answer. 

In your example,
"
>         .section .text1
> foo:    b        bar
> 
>         .section .text2
> bar:
"

If we take "b  bar" as a 32-bit instruction, then to get the relocation
information, of the label "bar", we can calculate the 'bar' value using
a 16-bit offset. 

If so, then it would be a 16-bit relocation.

Am I correct in assuming this?



> -----Original Message-----
> From: Richard Sandiford [mailto:rsandifo@redhat.com] 
> Sent: Friday, 19 December, 2003 20:34 PM
> To: gagneet@acmet.com
> Cc: gcc-help@gcc.gnu.org; gcc@gcc.gnu.org
> Subject: Re: ELF instruction for section and branch.
> 
> 
> "Gagneet Singh" <gagneet@acmet.com> writes:
> > I wish to enquire what is the equivalent for a assembly language 
> > section in the GCC ELF format?
> 
> I'm not quite sure what you mean here, but...
> 
> > Also, we have a problem of getting the output in ELF format where a 
> > branch instruction is accessing a label in the second section.
> >
> > Is this possible?
> 
> It sounds like you're asking about code such as:
> 
>         .section .text1
> foo:    b        bar
> 
>         .section .text2
> bar:
> 
> Is that right?  If so, then no, this isn't supported.  The 
> assembler can't calculate the branch offset because the 
> distance between foo and bar isn't known until link time.  
> And unfortunately, due to an infamous problem with the MIPS 
> ELF spec, there's no relocation that the assembler can use either.
> 
> (The R_MIPS_PC16 relocation was probably designed for 
> branches, but the ELF spec says it gives a byte offset, 
> whereas branch instructions need a word offset.)
> 
> Richard
> 



More information about the Gcc-help mailing list