Re: MIPS textrel fix

[Thiemo Seufer <ths at networkno dot de>]

David Daney wrote:
> Daniel Jacobowitz wrote:
> >While stuck offline earlier today, I revisited the textrel-1 MIPS
> >failure.  Eric originally tried setting DF_TEXTREL during section
> >relocation, but it's too late: we add the entry in size_dynamic_sections.
> >But I couldn't see any other way to get it right, since there's no
> >hook to predict whether elf-eh-frame.c will eliminate a relocation.
> >
> >The easiest approach I found was to annul the DT_TEXTREL and DT_FLAGS
> >changes in finish_dynamic_sections if no text relocations were
> >actually generated.  This is not immensely pretty, but does work.
> >OK?
> >
> >For background, the problem arises from the use of absolute addresses
> >in .eh_frame.  In this case, they're being produced by gas CFI
> >directives.  Is there a reason we can't mix and match encodings?
> >i.e. why not have gas use a PC-relative format?  I'm sure there's
> >a reason, but I can't think of it...
> >
> 
> Could it be related to the reason that GCC no longer generates a 
> PC-relative .eh_frame?
> 
> I never fully understood the reason, but I think it has to do with 
> MIPS-ELF specifications not allowing the needed relocation types (even 
> though they work well in binutils/glibc/linux).

The needed relocation types were originally defined for embedded PIC
MIPS and are not available in the ABI spec, their use for eh_frame
was an accident. When the removal of embedded PIC support broke the
toolchain, the fix chosen was to become ABI compatible again.


Thiemo