elna/backend/target.cpp

#include "elna/backend/target.hpp"
#include "elna/backend/riscv.hpp"
#include <elfio/elfio.hpp>

namespace elna::riscv
{
    void riscv32_elf(source::block *ast, const std::filesystem::path& out_file)
    {
        auto _visitor = std::make_unique<visitor>();
        _visitor->visit(ast);

        ELFIO::elfio writer;
        const ELFIO::Elf_Word instructions_size = _visitor->instructions.size() * sizeof(instruction);

        writer.create(ELFIO::ELFCLASS32, ELFIO::ELFDATA2LSB);

        writer.set_os_abi(ELFIO::ELFOSABI_NONE);
        writer.set_type(ELFIO::ET_REL);
        writer.set_machine(ELFIO::EM_RISCV);

        // Create code section
        ELFIO::section* text_sec = writer.sections.add(".text");
        text_sec->set_type(ELFIO::SHT_PROGBITS);
        text_sec->set_flags(ELFIO::SHF_ALLOC | ELFIO::SHF_EXECINSTR);
        text_sec->set_addr_align(0x1);
        text_sec->set_data(reinterpret_cast<const char *>(_visitor->instructions.data()),
                instructions_size);

        // Create string table section
        ELFIO::section* str_sec = writer.sections.add(".strtab");
        str_sec->set_type(ELFIO::SHT_STRTAB);

        // Create string table writer
        ELFIO::string_section_accessor stra(str_sec);

        // Create read only data section
        ELFIO::section* ro_sec = writer.sections.add(".rodata");
        ro_sec->set_type(ELFIO::SHT_PROGBITS);
        ro_sec->set_flags(ELFIO::SHF_ALLOC);
        ro_sec->set_addr_align(0x4);
        ro_sec->set_data("%d\n");

        // Create symbol table section
        ELFIO::section* sym_sec = writer.sections.add(".symtab");
        sym_sec->set_type(ELFIO::SHT_SYMTAB);
        sym_sec->set_info(2);
        sym_sec->set_addr_align(0x4);
        sym_sec->set_entry_size(writer.get_default_entry_size(ELFIO::SHT_SYMTAB));
        sym_sec->set_link(str_sec->get_index());

        // Create relocation table section
        ELFIO::section* rel_sec = writer.sections.add(".rel.text");
        rel_sec->set_type(ELFIO::SHT_REL);
        rel_sec->set_info(text_sec->get_index());
        rel_sec->set_addr_align(0x4);
        rel_sec->set_entry_size(writer.get_default_entry_size(ELFIO::SHT_REL));
        rel_sec->set_link(sym_sec->get_index());
        rel_sec->set_flags(ELFIO::SHF_ALLOC);

        // Create symbol relocation table writers
        ELFIO::symbol_section_accessor syma(writer, sym_sec);
        ELFIO::relocation_section_accessor rela(writer, rel_sec);
        ELFIO::Elf_Word digit_symbol = syma.add_symbol(stra, ".CL0", 0x00000000, strlen("%d\n") + 1,
                ELFIO::STB_LOCAL, ELFIO::STT_NOTYPE, 0, ro_sec->get_index());
        ELFIO::Elf_Word printf_symbol = syma.add_symbol(stra, "printf", 0x00000000, 0,
                ELFIO::STB_GLOBAL, ELFIO::STT_NOTYPE, 0, ELFIO::SHN_UNDEF);

        for (auto& reference : _visitor->references)
        {
            // The loop assumes that address_t::lower12i always follows address_t::high20.
            switch (reference.target)
            {
                case address_t::high20:
                    rela.add_entry(reference.offset, digit_symbol, 26 /* ELFIO::R_RISCV_HI20 */);
                    rela.add_entry(reference.offset, digit_symbol, 51 /* ELFIO::R_RISCV_RELAX */);
                    break;
                case address_t::lower12i:
                    rela.add_entry(reference.offset, digit_symbol, 27 /* ELFIO::R_RISCV_LO12_I */);
                    rela.add_entry(reference.offset, digit_symbol, 51 /* ELFIO::R_RISCV_RELAX */);
                    break;
                case address_t::text:
                    rela.add_entry(reference.offset, printf_symbol, 18 /* ELFIO::R_RISCV_CALL */);
                    rela.add_entry(reference.offset, printf_symbol, 51 /* ELFIO::R_RISCV_RELAX */);
                    break;
            }
        }
        syma.add_symbol(stra, "main", 0x00000000, instructions_size,
                ELFIO::STB_GLOBAL, ELFIO::STT_FUNC, 0, text_sec->get_index());

        // Create ELF object file
        writer.save(out_file);
    }
}