BinaryElfOutput

const BinaryElfOutput = struct

File

Code

const BinaryElfOutput = struct {
    segments: std.ArrayList(*BinaryElfSegment),
    sections: std.ArrayList(*BinaryElfSection),
    allocator: Allocator,
    shstrtab: ?[]const u8,

    const Self = @This();

    pub fn deinit(self: *Self) void {
        if (self.shstrtab) |shstrtab|
            self.allocator.free(shstrtab);
        self.sections.deinit(self.allocator);
        self.segments.deinit(self.allocator);
    }

    pub fn parse(allocator: Allocator, in: *File.Reader, elf_hdr: elf.Header) !Self {
        var self: Self = .{
            .segments = .empty,
            .sections = .empty,
            .allocator = allocator,
            .shstrtab = null,
        };
        errdefer self.sections.deinit(allocator);
        errdefer self.segments.deinit(allocator);

        self.shstrtab = blk: {
            if (elf_hdr.shstrndx >= elf_hdr.shnum) break :blk null;

            var section_headers = elf_hdr.iterateSectionHeaders(in);

            var section_counter: usize = 0;
            while (section_counter < elf_hdr.shstrndx) : (section_counter += 1) {
                _ = (try section_headers.next()).?;
            }

            const shstrtab_shdr = (try section_headers.next()).?;

            try in.seekTo(shstrtab_shdr.sh_offset);
            break :blk try in.interface.readAlloc(allocator, shstrtab_shdr.sh_size);
        };

        errdefer if (self.shstrtab) |shstrtab| allocator.free(shstrtab);

        var section_headers = elf_hdr.iterateSectionHeaders(in);
        while (try section_headers.next()) |section| {
            if (sectionValidForOutput(section)) {
                const newSection = try allocator.create(BinaryElfSection);

                newSection.binaryOffset = 0;
                newSection.elfOffset = section.sh_offset;
                newSection.fileSize = @intCast(section.sh_size);
                newSection.segment = null;

                newSection.name = if (self.shstrtab) |shstrtab|
                    std.mem.span(@as([*:0]const u8, @ptrCast(&shstrtab[section.sh_name])))
                else
                    null;

                try self.sections.append(allocator, newSection);
            }
        }

        var program_headers = elf_hdr.iterateProgramHeaders(in);
        while (try program_headers.next()) |phdr| {
            if (phdr.p_type == elf.PT_LOAD) {
                const newSegment = try allocator.create(BinaryElfSegment);

                newSegment.physicalAddress = phdr.p_paddr;
                newSegment.virtualAddress = phdr.p_vaddr;
                newSegment.fileSize = @intCast(phdr.p_filesz);
                newSegment.elfOffset = phdr.p_offset;
                newSegment.binaryOffset = 0;
                newSegment.firstSection = null;

                for (self.sections.items) |section| {
                    if (sectionWithinSegment(section, phdr)) {
                        if (section.segment) |sectionSegment| {
                            if (sectionSegment.elfOffset > newSegment.elfOffset) {
                                section.segment = newSegment;
                            }
                        } else {
                            section.segment = newSegment;
                        }

                        if (newSegment.firstSection == null) {
                            newSegment.firstSection = section;
                        }
                    }
                }

                try self.segments.append(allocator, newSegment);
            }
        }

        mem.sort(*BinaryElfSegment, self.segments.items, {}, segmentSortCompare);

        for (self.segments.items, 0..) |firstSegment, i| {
            if (firstSegment.firstSection) |firstSection| {
                const diff = firstSection.elfOffset - firstSegment.elfOffset;

                firstSegment.elfOffset += diff;
                firstSegment.fileSize += diff;
                firstSegment.physicalAddress += diff;

                const basePhysicalAddress = firstSegment.physicalAddress;

                for (self.segments.items[i + 1 ..]) |segment| {
                    segment.binaryOffset = segment.physicalAddress - basePhysicalAddress;
                }
                break;
            }
        }

        for (self.sections.items) |section| {
            if (section.segment) |segment| {
                section.binaryOffset = segment.binaryOffset + (section.elfOffset - segment.elfOffset);
            }
        }

        mem.sort(*BinaryElfSection, self.sections.items, {}, sectionSortCompare);

        return self;
    }

    fn sectionWithinSegment(section: *BinaryElfSection, segment: elf.Elf64_Phdr) bool {
        return segment.p_offset <= section.elfOffset and (segment.p_offset + segment.p_filesz) >= (section.elfOffset + section.fileSize);
    }

    fn sectionValidForOutput(shdr: anytype) bool {
        return shdr.sh_type != elf.SHT_NOBITS and
            ((shdr.sh_flags & elf.SHF_ALLOC) == elf.SHF_ALLOC);
    }

    fn segmentSortCompare(context: void, left: *BinaryElfSegment, right: *BinaryElfSegment) bool {
        _ = context;
        if (left.physicalAddress < right.physicalAddress) {
            return true;
        }
        if (left.physicalAddress > right.physicalAddress) {
            return false;
        }
        return false;
    }

    fn sectionSortCompare(context: void, left: *BinaryElfSection, right: *BinaryElfSection) bool {
        _ = context;
        return left.binaryOffset < right.binaryOffset;
    }
}