[LLVM][AVR] Support for R_AVR_6 fixup

[LemonBoy]

Summary

Handle the emission of R_AVR_6 ELF relocation type.

[LemonBoy]

Ping?

[dylanmckay]

Nice work @LemonBoy, thanks for the patch.

[LemonBoy]

In D78721#2028889, @dylanmckay wrote:

Nice work @LemonBoy, thanks for the patch.

If you could commit this on my behalf that'd be great. Once this is merged D78741 is unblocked.

[dylanmckay]

@LemonBoy merged in into master in 1335737ee119b59bc25ee6d1bb200cf3b975e196

llvm/lib/Target/AVR/MCTargetDesc/AVRAsmBackend.cpp

 static void fixup_13_pcrel(unsigned Size, const MCFixup &Fixup, uint64_t &Value,
                            MCContext *Ctx = nullptr) {
   adjustRelativeBranch(Size, Fixup, Value, Ctx);
 
   // Because the value may be negative, we must mask out the sign bits
   Value &= 0xfff;
 }
 
+/// 6-bit fixup for the immediate operand of the STD/LDD family of
+/// instructions.
+///
+/// Resolves to:
+/// 10q0 qq10 0000 1qqq
+static void fixup_6(const MCFixup &Fixup, uint64_t &Value,
+                    MCContext *Ctx = nullptr) {
+  unsigned_width(6, Value, std::string("immediate"), Fixup, Ctx);
+
+  Value = ((Value & 0x20) << 8) | ((Value & 0x18) << 7) | (Value & 0x07);
+}
+
 /// 6-bit fixup for the immediate operand of the ADIW family of
 /// instructions.
 ///
 /// Resolves to:
 /// 0000 0000 kk00 kkkk
 static void fixup_6_adiw(const MCFixup &Fixup, uint64_t &Value,
                          MCContext *Ctx = nullptr) {
   unsigned_width(6, Value, std::string("immediate"), Fixup, Ctx);
case AVR::fixup_16:
     break;
   case AVR::fixup_16_pm:
     Value >>= 1; // Flash addresses are always shifted.
     adjust::unsigned_width(16, Value, std::string("port number"), Fixup, Ctx);
 
     Value &= 0xffff;
     break;
 
+  case AVR::fixup_6:
+    adjust::fixup_6(Fixup, Value, Ctx);
+    break;
   case AVR::fixup_6_adiw:
     adjust::fixup_6_adiw(Fixup, Value, Ctx);
     break;
 
   case AVR::fixup_port5:
     adjust::fixup_port5(Fixup, Value, Ctx);
     break;
 

llvm/test/MC/AVR/relocations.s

 ; RUN: llvm-mc -filetype=obj -triple=avr %s -mattr=avr6 | llvm-objdump -r - | FileCheck %s
 
 ; CHECK: RELOCATION RECORDS FOR
 
 .global bar
 bar:
   jmp bar
 
 ; CHECK: R_AVR_LDI SYMBOL+0x3
 ldi r21, SYMBOL+3
 
+; CHECK: R_AVR_6 SYMBOL+0x4
+ldd r8, Y+SYMBOL+4
+
 ; CHECK-NEXT: R_AVR_6_ADIW FOO
 adiw r24, FOO
 
 ; CHECK-NEXT: R_AVR_16 BAR+0x2
 lds r8, BAR+2
 
 ; CHECK-NEXT: R_AVR_PORT5 foo
 sbic foo, 1