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8c1f87a869
Cast through the integer of an appropriate size. This still generates a 64-bit ELF image.
87 lines
3.2 KiB
C++
87 lines
3.2 KiB
C++
/*
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* Copyright (c) 2023, Jesús Lapastora <cyber.gsuscode@gmail.com>
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*
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* SPDX-License-Identifier: BSD-2-Clause
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*/
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#include <LibELF/ELFBuild.h>
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#include <LibJIT/GDB.h>
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namespace JIT::GDB {
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Optional<FixedArray<u8>> build_gdb_image(ReadonlyBytes code, StringView file_symbol_name, StringView code_symbol_name)
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{
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Vector<Elf64_Sym> symbols;
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ELF::StringTable section_names;
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ELF::StringTable symbol_names;
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ELF::SectionTable sections;
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auto const null_section = sections.build_null();
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// empty name so that its name in the dump isn't confused with '.text'.
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sections.header_at(null_section).sh_name = section_names.insert(""sv);
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// Build .text as a NOBITS section since the code isn't loaded inside the
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// image. The image just holds the addresses for the executable region.
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auto const text = sections.build_nobits([&](Elf64_Shdr& text) {
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text.sh_name = section_names.insert(".text"sv);
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text.sh_flags = SHF_EXECINSTR | SHF_ALLOC;
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text.sh_addr = bit_cast<uintptr_t>(code.offset(0));
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text.sh_size = code.size();
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text.sh_link = 0;
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text.sh_info = 0;
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text.sh_addralign = 1;
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text.sh_entsize = 0;
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});
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// Without this, GDB won't show the symbol names for our code.
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Elf64_Sym file;
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{
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file.st_name = symbol_names.insert(file_symbol_name);
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file.st_info = ELF64_ST_INFO(STB_GLOBAL, STT_FILE);
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file.st_other = STV_DEFAULT;
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file.st_shndx = SHN_ABS;
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file.st_value = 0;
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file.st_size = code.size();
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}
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symbols.append(file);
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// The index of the first symbol that does not have a `STB_LOCAL` binding.
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// Note that all non-local bindings must come before all local bindings.
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auto const first_non_local_symbol_index = symbols.size();
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Elf64_Sym code_sym;
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{
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code_sym.st_name = symbol_names.insert(code_symbol_name);
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code_sym.st_info = ELF64_ST_INFO(STB_GLOBAL, STT_FUNC);
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code_sym.st_other = STV_DEFAULT;
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code_sym.st_shndx = text.index,
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code_sym.st_value = 0; // 0 bytes relative to .text
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code_sym.st_size = code.size();
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}
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symbols.append(code_sym);
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auto const strtab = symbol_names.emit_into_builder(
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section_names.insert(".strtab"sv), sections);
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sections.build<Elf64_Sym>(symbols.span(),
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[§ion_names, first_non_local_symbol_index, strtab](Elf64_Shdr& symtab) {
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symtab.sh_name = section_names.insert(".symtab"sv);
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symtab.sh_type = SHT_SYMTAB;
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symtab.sh_flags = 0;
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symtab.sh_addr = 0;
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symtab.sh_info = first_non_local_symbol_index;
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symtab.sh_link = strtab.raw_index();
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symtab.sh_addralign = 0;
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});
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// Make sure we find where the name for .shstrtab resides before we insert
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// it into the image.
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auto const shstrtab_name_index = section_names.insert(".shstrtab"sv);
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auto const shstrtab = section_names.emit_into_builder(
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shstrtab_name_index, sections);
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// Set the type to an "object" file, as GDB seems to request it:
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// https://sourceware.org/gdb/current/onlinedocs/gdb.html/Registering-Code.html#Registering-Code
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return ELF::build_elf_image(shstrtab.raw_index(), ET_REL, sections.span());
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}
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}
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