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23 Load and Store Global

The following pseudoinstructions are available to load from and store to global objects:

  • l\{b|h|w|d\} \<rd\>, \<symbol expression\>: load byte, half word, word or double word from global

  • l\{bu|hu|wu\} \<rd\>, \<symbol expression\>: load unsigned byte, half word, or word from global

  • s\{b|h|w|d\} \<rd\>, \<symbol expression\>, \<rt\>: store byte, half word, word or double word to global

  • fl\{h|w|d|q\} \<rd\>, \<symbol expression\>, \<rt\>: load half, float, double or quad precision from global

  • fs\{h|w|d|q\} \<rd\>, \<symbol expression\>, \<rt\>: store half, float, double or quad precision to global

The following example shows how these pseudoinstructions are used:

  lw  a0, var1
  fld fa0, var2, t0
  sw  a0, var3, t0
  fsd fa0, var4, t0

Which generates the following assembler output and relocations as seen by objdump:

0000000000000000 \<.text>:
   0: 00000517            auipc a0,0x0
      0: R_RISCV_PCREL_HI20 var1
   4: 00052503            lw  a0,0(a0) # 0 \<.text>
      4: R_RISCV_PCREL_LO12_I .L0
   8: 00000297            auipc t0,0x0
      8: R_RISCV_PCREL_HI20 var2
   c: 0002b507            fld fa0,0(t0) # 8 \<.text+0x8>
      c: R_RISCV_PCREL_LO12_I .L0
  10: 00000297            auipc t0,0x0
      10: R_RISCV_PCREL_HI20  var3
  14: 00a2a023            sw  a0,0(t0) # 10 \<.text+0x10>
      14: R_RISCV_PCREL_LO12_S  .L0
  18: 00000297            auipc t0,0x0
      18: R_RISCV_PCREL_HI20  var4
  1c: 00a2b027            fsd fa0,0(t0) # 18 \<.text+0x18>
      1c: R_RISCV_PCREL_LO12_S  .L0

On RV32, ld \<rd>, \<symbol expression> and sd \<rd>, \<symbol expression>, \<rt> can be used to generate a sequence including the ld and sd instructions in Zilsd — in these cases, \<rd> denotes the even GPR in an even-odd GPR pair.