[PATCH] D35544: [COFF, ARM64] Force ADRP relocations

[Martin Storsjö via Phabricator via llvm-commits]

mstorsjo added a comment.

In https://reviews.llvm.org/D35544#812979, @t.p.northover wrote:

> > I'd be interested in knowing why this isn't done by default (i.e. why this doesn't need to be done at all for MachO) btw, if someone has got time to explain.
>
> I'm pretty sure that's a bug, I get the wrong answer when I actually try out this function on iOS:
>
>           .text
>           .global _foo
>           .p2align 12
>   _foo:
>           .fill 1023, 4, 0xd503201f
>           adrp x0, Lthere
>   Lthere:
>           ret
>   
>
> I suspect it hasn't come up on MachO because CodeGen never used ADRP to address objects in the __text section so you need assembly to trigger it.


I did a quick test like this:

  static int the_func(int a);
                  
  void *get_func(void) {
          return the_func;
  }
  
  static int the_func(int a) {
          return 2*a;
  }

and got this:

  $ clang test.c -c -o test.o -O3 -target arm64-apple-darwin
  $ llvm-objdump -d -r test.o
  
  test.o:  file format Mach-O arm64
  
  Disassembly of section __TEXT,__text:
  ltmp0:
         0:       00 00 00 90     adrp    x0, #0
                  0000000000000000:  ARM64_RELOC_PAGE21   _the_func
         4:       00 00 00 91     add     x0, x0, #0
                  0000000000000004:  ARM64_RELOC_PAGEOFF12        _the_func
         8:       c0 03 5f d6     ret
  
  _the_func:
         c:       00 78 1f 53     lsl     w0, w0, #1
        10:       c0 03 5f d6     ret

So it seems to me like it actually does use ADRP, but probably via some other codepath, since it does generate a relocation. But fixing it for handwritten assembly obviously also is worthwhile.

> So would you mind putting that function into the base AArch64AsmBackend?

Sure, will do.


https://reviews.llvm.org/D35544