Add GP-relative relocations

Author: luismarques

riscv-elf.adoc

@@ -452,7 +452,13 @@ Description:: Additional information about the relocation
                                             <| S + A
 .2+| 61      .2+| SUB_ULEB128   .2+| Static  | _ULEB128_         .2+| Local label subtraction <<uleb128-note,*note>>
                                             <| V - S - A
-.2+| 62-191  .2+| *Reserved*                          .2+| -       |                   .2+| Reserved for future standard use
+.2+| 62      .2+| GPREL_HI20    .2+| Static  | _U-Type_          .2+| High 20 bits of a 32-bit GP-relative address, `%gprel_hi(symbol)`
+                                            <| S + A - GP
+.2+| 63      .2+| GPREL_LO12_I  .2+| Static  | _I-type_          .2+| Low 12 bits of a 32-bit GP-relative address, `%gprel_lo(symbol)`
+                                            <| S + A - GP
+.2+| 64      .2+| GPREL_LO12_S  .2+| Static  | _S-Type_          .2+| Low 12 bits of a 32-bit GP-relative address, `%gprel_lo(symbol)`
+                                            <| S + A - GP
+.2+| 65-191  .2+| *Reserved*                          .2+| -       |                   .2+| Reserved for future standard use
                                             <|
 .2+| 192-255 .2+| *Reserved*                          .2+| -       |                   .2+| Reserved for nonstandard ABI extensions
                                             <|