[PATCH] MIPS: support PCREL GOT access

[Maciej W. Rozycki]

On Mon, 5 Feb 2024, Nick Clifton wrote:

> > Any idea how to write ld testcases?
> > Normal readelf/objdump can only be sure that it is linked.
> > I think that we need to execute the out objects to be sure that it has no
> > problems, such as segfault etc.
> 
> You can use the [isnative] test to check to see if the test
> is being run natively and then try executing the linked code.

 This will limit verification however, especially for such a target as the 
MIPS one, usually found in embedded devices only and therefore typically 
only verified in a cross-environment.  I can't remember when I last run 
verification with the MIPS target natively if ever.  It just takes too 
long for regular use, and it can obviously only cover whatever the subset 
of ISA features is that the native system provides.

 The proper way to handle such verification is to tighten the test cases.  
Relocations have well-defined semantics, so you can prepare sources such 
as to get reproducible output you can then match against.  That means 
verifying exact bit patterns in files produced, and you can arrange for 
boundary cases, such as carry/borrow or overflow, to be verified where 
applicable too.  We have such detailed cases in our testsuite already.

 Relying on run-time tests to crash if a relocation calculation goes wrong 
seems rather fragile to me.  I can imagine errors to cancel each other for 
example.

  Maciej