Add R_HEX_GOT_16_X support

[sidneym]

Summary

Wow! Just 280 lines of target-specific code and lld will link both the linux kernel and musl libc.so for hexagon.

[ruiu]

LGTM

Congratulations! I'm happy to see this concrete example that lld is *very* hackable and extremely easy to extend. :) We've been emphasizing simplicity, and it surely pays off.

[ruiu]

Sid,

Is this your final patch to support Hexagon, or do you have any other plans? I'm just wondering.

[sidneym]

No this isn't, I'd like to add TLS support. I'm also sure some additional relocations will be required (beyond the TLS ones).

ELF/Arch/Hexagon.cpp

   case R_HEX_B32_PCREL_X:
     return R_PLT_PC;
   case R_HEX_GOT_11_X:
+  case R_HEX_GOT_16_X:
   case R_HEX_GOT_32_6_X:
     return R_HEXAGON_GOT;
   default:

   case R_HEX_12_X:
     or32le(Loc, applyMask(0x000007e0, Val));
     break;
-  case R_HEX_16_X: // This reloc only has 6 effective bits.
+  case R_HEX_16_X: // These relocs only have 6 effective bits.
+  case R_HEX_GOT_16_X:
     or32le(Loc, applyMask(findMaskR16(read32le(Loc)), Val & 0x3f));
     break;
   case R_HEX_32:

test/ELF/hexagon-shared.s

 r0 = memw (r2+##bar@GOT)
 jumpr r0
 
+# R_HEX_GOT_16_X
+r0 = add(r1,##bar@GOT)
+
 # PLT: { immext(#65472
 # PLT: r28 = add(pc,##65488) }
 # PLT: { r14 -= add(r28,#16)

 
 # TEXT:  10000: 00 00 02 00 00020000
 # TEXT: {   call 0x10050 }
+# TEXT: r0 = add(r1,##65664) }
 
 # GOT: .got:
 # GOT: 30080: 00 00 00 00 00000000 <unknown>