Fix new -Werror compiler warnings in binutils

[arichardson]

Summary

Latest clang git has a warning -Wnull-pointer-arithmetic which will trigger
a -Werror failure. Addition and subtraction from a null pointer is
undefined behaviour and could be optimized into anything. Furthermore,
using the difference between two pointers and casting the result back to a
pointer is not portable since the size of ptrdiff_t does not necessary
have to be the same as size of void* (this happens e.g. on CHERI). Using
intptr_t instead fixes this portability issue and the compiler warning.

Obtained from: CheriBSD

Test Plan

I can now compile binutils with latest clang HEAD.

[theraven]

I don't have strong opinions about this - hopefully this code can be fixed by some judicious application of svn rm in the near future...

contrib/binutils/include/obstack.h

116 ↗

(On Diff #34712)

C doesn't require that int* and void* have the same representation. On some (very) old machines, loads and stores worked only at the granularity of a machine word (typically 16 bits, though sometimes larger). An int* on such a machine was represented as a (word) address, but a char* might be a pair of an address and a byte offset. Accessing a char required a load an a shift or mask.

I think binutils still supports at least one such architecture (though FreeBSD doesn't).

Generally, I think we lower WARNS on contrib code, especially poor-quality GNU code, though when the fix is this simple it might be worth retaining - especially as binutils is due a de-orbit burn soon and is unlikely to ever receive an update..

[jhb]

I would probably be inclined to just add -Wno-foo to WARNFLAGS.clang with a suitable compiler version check instead if this generates equivalent code for non-CHERI. (For CHERI I think we can just always build ld.bfd as a plain MIPS binary while we still need ld.bfd).

[arichardson]

removed unnecessary comment

[emaste]

No objection from me.

[dim]

I'm going to commit this now, since we need it in the clang600-import branch.