title	date	categories	tags
RISC-V Code Model	2024-06-13 17:30:00 +0800	RISC-V	code model risc-v

RISC-V only has three addressing modes:

• PC-relative, via the auipc, jal and br* instructions.
• Register-offset, via the jalr, addi and all memory instructions.
• Absolute, via the lui instruction (though arguably this is just x0-offset).

medlow

The program and its statically defined symbols must lie within a single 2 GiB address range and must lie between absolute addresses −2 GiB and +2 GiB. Programs can be statically or dynamically linked.

lui a0, xxxx
addi a0, a0, xxxx

• 32 位

  lui：R[rd] = { imm, 12'b0 }

  范围为 0x0000 0000 - 0xffff f000。

  addi: R[rd] = R[rs1] + imm(sign-ext)

  范围为 0x0000 0000 - 0xffff ffff。

• 64 位

  lui：R[rd] = { 32b'imm<31>, imm, 12'b0 }

  imm<31> 为 0，范围为 0x0000 0000 0000 0000 - 0x0000 0000 7fff f000。

  imm<31> 为 1，范围为 0xffff ffff 8000 0000 - 0xffff ffff ffff f000。

  addi: R[rd] = R[rs1] + imm(sign-ext)

  imm 第 11 位为 0，0x0000 0000 0000 0000 - 0x0000 0000 0000 07ff。

  imm 第 11 位为 1，0xffff ffff ffff f800 - 0xffff ffff ffff ffff。

  最后范围为 0x0 - 0x000000007FFFF7FF 0xFFFFFFFF7FFFF800 - 0xFFFFFFFFFFFFFFFF。

medany

The program and its statically defined symbols must be within any single 2 GiB address range. Programs can be statically or dynamically linked.

• Function

          mutex_lock(&nf_conn_btf_access_lock);
  ffffffff80733316:  0017c097  auipc   ra,0x17c
  ffffffff8073331a:  76e080e7  jalr    1902(ra) # ffffffff808afa84 <mutex_lock>
  

• Variable

Reference

https://www.sifive.com/blog/all-aboard-part-4-risc-v-code-models

https://gcc.gnu.org/onlinedocs/gcc/RISC-V-Options.html