Implement RISC-V dynamic linking

[DrXiao]

The proposed changes primarily improve the ELF generation and the RISC-V backend, enabling the build system to generate a dynamically linked shecc targeting the RISC-V architecture.

Although the current changes allow both bootstrapping and test suite to complete successfully, this is still a work in progress. The TODO items are listed as follows:

• Enhance code quality, comments and commit messages.
• Confirm the RISC-V ABI compliance.
• Add a new script (riscv-abi.sh) to validate the RISC-V ABI.
• Improve the documentation and README.
• Consolidate arm.mk and riscv.mk into a common build logic (e.g.: configure RUNNER_LD_PREFIX).
• (Any new requirements ...)

---

Summary by cubic

Adds dynamic linking support for RISC-V (rv32). The compiler now emits RELA-based PLT/GOT, calls external functions via PLT, and starts via __libc_start_main; CI and build updates validate dynamic RV32 builds.

• New Features

  • Enable RISC-V dynamic linking with .rela.plt, RELA entries, and RV32 GOT/PLT sizes; reserve 2 GOT slots for the resolver/link_map.
  • Generate RV32 PLT stubs and call externs via PLT; entry uses __libc_start_main; align stacks and preserve ra; keep syscall trampoline for static builds.
  • Refactor ELF to support REL or RELA via a use_relaplt flag, add arch constants, and emit correct dynamic tags/headers; initialize .got using RESERVED_GOT_NUM.
  • Build/test: allow DYNLINK=1 for RISC-V, add RV32 dynamic snapshots, and run static/dynamic matrices for ARM and RISC-V.

• Dependencies

  • CI installs a RISC-V glibc toolchain and adds it to PATH; mk/riscv.mk locates ld-linux and sets RUNNER_LD_PREFIX under QEMU for dynamic runs.

^{Written for commit 446b538. Summary will update on new commits.}

[DrXiao]

As the apt package manager only provides a 64-bit RISC-V GNU cross-compilation toolchain, I utilize riscv-gnu-toolchain , which is a 32-bit variant, and leverage its artifacts for RISC-V dynamic linking development and validation.

The updated GitHub Actions also downloads the 32-bit variant to validate RISC-V dynamic linking.

[jserv]

As the apt package manager only provides a 64-bit RISC-V GNU cross-compilation toolchain, I utilize riscv-gnu-toolchain , which is a 32-bit variant, and leverage its artifacts for RISC-V dynamic linking development and validation.
The updated GitHub Actions also downloads the 32-bit variant to validate RISC-V dynamic linking.

Evaluate Run 32-bit applications on 64-bit Linux kernel, which is exactly RV32-on-RV64 userspace compatibility, not emulation.

[DrXiao]

Evaluate Run 32-bit applications on 64-bit Linux kernel, which is exactly RV32-on-RV64 userspace compatibility, not emulation.

I'm not sure whether I understand correctly. Do you mean that the proposed changes should be verified on a RISC-V machine?

[jserv]

Do you mean that the proposed changes should be verified on a RISC-V machine?

See sysprog21/kbox#18
The RISE RISC-V Runners is a managed GitHub Actions runner service that executes CI/CD workflows on real RISC-V hardware.