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Re: [PATCH] MIPS: Use R_MICROMIPS_JALR rather than R_MIPS_JALR in microMIPS code

On Wed, 23 Nov 2016, Joseph Myers wrote:

> >  OK to apply?
> OK.

 Applied, thanks.

> It would probably make sense to add at least one mips16 and one microMIPS 
> configuration to so build failures for such 
> configurations are more readily detected (though I suppose a wrong 
> relocation like this might not result in a build failure?).

 In the R_MIPS_JALR case BFD linker code checks the opcode of the 
instruction at the relocation location so that JALR and JR (for tail 
calls) are substituted with BAL and J respectively, and the microMIPS 
encodings are different, so no match happens and an invalid relocation is 
silently ignored.  So no build failure will ever happen indeed.

 The R_MICROMIPS_JALR case is more complicated and currently not handled 
by the BFD linker at all, with the relocation always silently ignored, 
though I plan to get to it sometime.  Most transformations are limited by 
the assymetry of the 16-bit instruction set, however some can still be 
made, e.g. JR16 can be changed into B16, and all can still be made in the 
`-minsn32' mode (which is however hardly ever used).  This is probably the 
reason why it hasn't been implemented with the original microMIPS effort.

 I have no idea what GOLD does with these relocations, although I suppose 
any handling will have been semantically copied from the BFD linker.


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