[AArch64] Add support for got relocated LDR's

[dmgreen]

Summary

As a part of adding the tiny codemodel, we need to support ldr's with :got: relocations on them. This seems to be mostly already done, just needs the relocation type support.

Pulled out of D49673.

[t.p.northover]

Looks fine to me.

[dmgreen]

Thanks

lib/Target/AArch64/MCTargetDesc/AArch64ELFObjectWriter.cpp

case AArch64::fixup_aarch64_pcrel_adrp_imm21:
       return ELF::R_AARCH64_NONE;
     case AArch64::fixup_aarch64_pcrel_branch26:
       return R_CLS(JUMP26);
     case AArch64::fixup_aarch64_pcrel_call26:
       return R_CLS(CALL26);
     case AArch64::fixup_aarch64_ldr_pcrel_imm19:
       if (SymLoc == AArch64MCExpr::VK_GOTTPREL)
         return R_CLS(TLSIE_LD_GOTTPREL_PREL19);
+      if (SymLoc == AArch64MCExpr::VK_GOT)
+        return R_CLS(GOT_LD_PREL19);
       return R_CLS(LD_PREL_LO19);
     case AArch64::fixup_aarch64_pcrel_branch14:
       return R_CLS(TSTBR14);
     case AArch64::fixup_aarch64_pcrel_branch19:
       return R_CLS(CONDBR19);
     default:
       Ctx.reportError(Fixup.getLoc(), "Unsupported pc-relative fixup kind");
       return ELF::R_AARCH64_NONE;

test/MC/AArch64/arm64-elf-relocs.s

 // tests, as it isn't a TLS relocation.
 // CHECK-ENCODING: ldr q20, [x19, :lo12:sym] // encoding: [0x74,0bAAAAAA10,0b11AAAAAA,0x3d]
 // CHECK-ENCODING-NEXT:  0, value: :lo12:sym, kind: fixup_aarch64_ldst_imm12_scale16
 
 // Since relocated instructions print without a '#', that syntax should
 // certainly be accepted when assembling.
    add x3, x5, :lo12:imm
 // CHECK: add x3, x5, :lo12:imm
+
+   ldr x24, #:got:sym
+   ldr d22, :got:sym
+// CHECK: ldr x24, :got:sym
+// CHECK: ldr d22, :got:sym
+// CHECK-OBJ-LP64: R_AARCH64_GOT_LD_PREL19 sym
+// CHECK-OBJ-LP64: R_AARCH64_GOT_LD_PREL19 sym
 No newline at end of file

test/MC/AArch64/elf-reloc-pcreladdressing.s

 // RUN: llvm-mc -triple=aarch64-none-linux-gnu -filetype=obj %s -o - | \
 // RUN:   llvm-readobj -r | FileCheck -check-prefix=OBJ %s
 
         adr x2, some_label
         adrp x5, some_label
 
         adrp x5, :got:some_label
         ldr x0, [x5, #:got_lo12:some_label]
 
+        ldr x0, :got:some_label
+
 // OBJ:      Relocations [
 // OBJ-NEXT:   Section {{.*}} .rela.text {
 // OBJ-NEXT:     0x0 R_AARCH64_ADR_PREL_LO21    some_label 0x0
 // OBJ-NEXT:     0x4 R_AARCH64_ADR_PREL_PG_HI21 some_label 0x0
 // OBJ-NEXT:     0x8 R_AARCH64_ADR_GOT_PAGE     some_label 0x0
 // OBJ-NEXT:     0xC R_AARCH64_LD64_GOT_LO12_NC some_label 0x0
+// OBJ-NEXT:     0x10 R_AARCH64_GOT_LD_PREL19   some_label 0x0
 // OBJ-NEXT:   }
 // OBJ-NEXT: ]

test/MC/AArch64/inline-asm-modifiers.s

// %bb.0:
   adrp x0, :got:var_got
   //NO_APP
   //APP
   adrp x0, :tlsdesc:var_tlsgd
   //NO_APP
   //APP
   adrp x0, :gottprel:var_tlsie
   //NO_APP
+  //APP
+  ldr x0, :got:var_got
+  //NO_APP
   ret
 .Ltmp2:
   .size test_inline_modifier_A, .Ltmp2-test_inline_modifier_A
 // CHECK: R_AARCH64_ADR_PREL_PG_HI21 var_simple
 // CHECK: R_AARCH64_ADR_GOT_PAGE var_got
 // CHECK: R_AARCH64_TLSDESC_ADR_PAGE21 var_tlsgd
 // CHECK: R_AARCH64_TLSIE_ADR_GOTTPREL_PAGE21 var_tlsie
+// CHECK: R_AARCH64_GOT_LD_PREL19 var_got
 
   .globl  test_inline_modifier_wx
   .type test_inline_modifier_wx,@function
 test_inline_modifier_wx:                // @test_inline_modifier_wx
 // %bb.0:
   mov  w2, w0
   //APP
   add w2, w2, w2