[lld] [ELF/AArch64] Simplify AArch64 isRelRelative

[zatrazz]

Summary

This patch simplifies the isRelRelative for AArch64 to just handle the
cases where it is not relative, instead of list all the relocations
that is. It also adds more testing for shared objects creation.

[• rafael]

bool AArch64TargetInfo::isRelRelative(uint32_t Type) const {

• return Type == R_AARCH64_PREL32 || Type == R_AARCH64_ADR_PREL_PG_HI21 ||
• Type == R_AARCH64_LDST8_ABS_LO12_NC ||
• Type == R_AARCH64_LDST32_ABS_LO12_NC ||
• Type == R_AARCH64_LDST64_ABS_LO12_NC ||
• Type == R_AARCH64_ADD_ABS_LO12_NC || Type == R_AARCH64_CALL26;

+ switch (Type) {
+ default:
+ return true;
+ case R_AARCH64_ABS64:
+ case R_AARCH64_ADR_GOT_PAGE:
+ case R_AARCH64_LD64_GOT_LO12_NC:
+ return !Config->Shared;

I don't think this makes sense. The relocations have different
definitions depending on -shared? If not, how come they become
relative or not depending on -shared?

Cheers,
Rafael

[zatrazz]

In D18031#371973, @rafael wrote:

bool AArch64TargetInfo::isRelRelative(uint32_t Type) const {

• return Type == R_AARCH64_PREL32 || Type == R_AARCH64_ADR_PREL_PG_HI21 ||
• Type == R_AARCH64_LDST8_ABS_LO12_NC ||
• Type == R_AARCH64_LDST32_ABS_LO12_NC ||
• Type == R_AARCH64_LDST64_ABS_LO12_NC ||
• Type == R_AARCH64_ADD_ABS_LO12_NC || Type == R_AARCH64_CALL26;

+ switch (Type) {
+ default:
+ return true;
+ case R_AARCH64_ABS64:
+ case R_AARCH64_ADR_GOT_PAGE:
+ case R_AARCH64_LD64_GOT_LO12_NC:
+ return !Config->Shared;

I don't think this makes sense. The relocations have different
definitions depending on -shared? If not, how come they become
relative or not depending on -shared?

Cheers,
Rafael

They do have different semantics depending if the code is position independent (which it is not only shared, but also PIE executables) and this method is used to define whether we will emit or not a dynamic relocation. If you check, gold is doing pretty much this in its local scan.

[zatrazz]

Ping.

ELF/Target.cpp

 bool AArch64TargetInfo::isTlsDescRel(unsigned Type, const SymbolBody &S) const {
   return Type == R_AARCH64_TLSDESC_ADR_PAGE21 ||
          Type == R_AARCH64_TLSDESC_LD64_LO12_NC ||
          Type == R_AARCH64_TLSDESC_ADD_LO12_NC ||
          Type == R_AARCH64_TLSDESC_CALL;
 }
 
 bool AArch64TargetInfo::isRelRelative(uint32_t Type) const {
-  return Type == R_AARCH64_PREL32 || Type == R_AARCH64_ADR_PREL_PG_HI21 ||
-         Type == R_AARCH64_LDST8_ABS_LO12_NC ||
-         Type == R_AARCH64_LDST32_ABS_LO12_NC ||
-         Type == R_AARCH64_LDST64_ABS_LO12_NC ||
-         Type == R_AARCH64_ADD_ABS_LO12_NC || Type == R_AARCH64_CALL26;
+  switch (Type) {
+  default:
+    return true;
+  case R_AARCH64_ABS64:
+  case R_AARCH64_ADR_GOT_PAGE:
+  case R_AARCH64_LD64_GOT_LO12_NC:
+    return !Config->Shared;
+  }
 }
 
 bool AArch64TargetInfo::isTlsInitialExecRel(uint32_t Type) const {
   return Type == R_AARCH64_TLSIE_ADR_GOTTPREL_PAGE21 ||
          Type == R_AARCH64_TLSIE_LD64_GOTTPREL_LO12_NC;
 }
 
 uint32_t AArch64TargetInfo::getDynRel(uint32_t Type) const {

test/ELF/aarch64-relative.s

 // REQUIRES: aarch64
 // RUN: llvm-mc -filetype=obj -triple=aarch64-unknown-freebsd %s -o %t.o
 // RUN: ld.lld %t.o -o %t.so -shared
 // RUN: llvm-readobj -r %t.so | FileCheck %s
-        adrp    x8, .Lfoo
-        strb    w9, [x8, :lo12:.Lfoo]
-        ldr     w0, [x8, :lo12:.Lfoo]
-        ldr     x0, [x8, :lo12:.Lfoo]
-        add     x0, x0, :lo12:.Lfoo
-        bl      .Lfoo
 
+        adr     x8, .Lfoo                 // R_AARCH64_ADR_PREL_LO21
+        adrp    x8, .Lfoo                 // R_AARCH64_ADR_PREL_PG_HI21
+        strb    w9, [x8, :lo12:.Lfoo]     // R_AARCH64_LDST8_ABS_LO12_NC
+        ldr     h17, [x19, :lo12:.Lfoo]   // R_AARCH64_LDST16_ABS_LO12_NC
+        ldr     w0, [x8, :lo12:.Lfoo]     // R_AARCH64_LDST32_ABS_LO12_NC
+        ldr     x0, [x8, :lo12:.Lfoo]     // R_AARCH64_LDST64_ABS_LO12_NC
+        ldr     q20, [x19, #:lo12:.Lfoo]  // R_AARCH64_LDST128_ABS_LO12_NC
+        add     x0, x0, :lo12:.Lfoo       // R_AARCH64_ADD_ABS_LO12_NC
+        bl      .Lfoo                     // R_AARCH64_CALL26
+        b       .Lfoo                     // R_AARCH64_JUMP26
+        beq     .Lfoo                     // R_AARCH64_CONDBR19
+        adr     x1, .Lfoo                 // R_AARCH64_ADR_PREL_LO21
+        tbz     x1, 7, .Lfoo              // R_AARCH64_TSTBR14
         .data
         .Lfoo:
 
         .rodata
         .long .Lfoo - .
 
 // CHECK:      Relocations [
 // CHECK-NEXT: ]