tiny.tldr.formats.elf.ehframe.record

1const std = @import("std");2const root = @import("../../../root.zig");3const elf = @import("../root.zig");45const model = root.model;6const Rela = elf.format.Rela;7const readU32 = elf.format.readU32;89pub const Cursor = struct {10    relocations: []const Rela,11    index: usize = 0,12    sorted: bool,1314    pub fn init(relocations: []const Rela) Cursor {15        return .{16            .relocations = relocations,17            .sorted = sortedByOffset(relocations),18        };19    }2021    pub fn at(self: *Cursor, offset: u64) ?Rela {22        if (!self.sorted) return scanAt(self.relocations, offset);23        while (self.index < self.relocations.len and self.relocations[self.index].offset < offset) self.index += 1;24        var run = self.index;25        while (run < self.relocations.len and self.relocations[run].offset == offset) : (run += 1) {26            if (!elf.relocation.isNone(self.relocations[run])) return self.relocations[run];27        }28        return null;29    }3031    pub fn window(self: *Cursor, start_offset: u64, end_offset: u64) ?[]const Rela {32        if (!self.sorted) return null;33        while (self.index < self.relocations.len and self.relocations[self.index].offset < start_offset) self.index += 1;34        const window_start = self.index;35        while (self.index < self.relocations.len and self.relocations[self.index].offset < end_offset) self.index += 1;36        return self.relocations[window_start..self.index];37    }38};3940pub fn hasHeaderEntry(41    bytes: []const u8,42    input_offset: u64,43    size: u64,44    output_offset: u64,45    cursor: *Cursor,46) model.Error!bool {47    if (size < 4) return error.InvalidObject;48    const start: usize = @intCast(input_offset);49    if (bytes.len - start < 4) return error.InvalidObject;50    const record_length = readU32(bytes, start);51    if (record_length == 0) return false;52    if (record_length == 0xffffffff) return error.UnsupportedFormat;53    if (size < @as(u64, record_length) + 4) return error.InvalidObject;54    if (record_length < 4) return error.InvalidObject;55    const record_id = readU32(bytes, start + 4);56    if (record_id == 0) return false;57    return cursor.at(output_offset + 8) != null;58}5960fn sortedByOffset(relocations: []const Rela) bool {61    if (relocations.len < 2) return true;62    for (relocations[0 .. relocations.len - 1], relocations[1..]) |previous, next| {63        if (next.offset < previous.offset) return false;64    }65    return true;66}6768fn scanAt(relocations: []const Rela, offset: u64) ?Rela {69    for (relocations) |relocation| {70        if (relocation.offset == offset and !elf.relocation.isNone(relocation)) return relocation;71    }72    return null;73}7475test "eh frame relocation cursor answers monotone queries" {76    const none_type: u32 = @backingInt(std.elf.R_X86_64.NONE);77    const pc32_type: u32 = @backingInt(std.elf.R_X86_64.PC32);78    const relocations = [_]Rela{79        .{ .offset = 8, .info = (@as(u64, 1) << 32) | pc32_type, .addend = 0 },80        .{ .offset = 16, .info = (@as(u64, 2) << 32) | none_type, .addend = 0 },81        .{ .offset = 16, .info = (@as(u64, 3) << 32) | pc32_type, .addend = 4 },82        .{ .offset = 40, .info = (@as(u64, 4) << 32) | pc32_type, .addend = 0 },83    };8485    var cursor = Cursor.init(&relocations);86    try std.testing.expect(cursor.sorted);87    try std.testing.expectEqual(@as(i64, 0), cursor.at(8).?.addend);88    try std.testing.expectEqual(@as(u32, 3), cursor.at(16).?.symbolIndex());89    try std.testing.expectEqual(@as(u32, 3), cursor.at(16).?.symbolIndex());90    try std.testing.expect(cursor.at(24) == null);91    try std.testing.expectEqual(@as(u32, 4), cursor.at(40).?.symbolIndex());92}9394test "eh frame relocation cursor extracts consuming windows" {95    const pc32_type: u32 = @backingInt(std.elf.R_X86_64.PC32);96    const relocations = [_]Rela{97        .{ .offset = 8, .info = (@as(u64, 1) << 32) | pc32_type, .addend = 0 },98        .{ .offset = 24, .info = (@as(u64, 2) << 32) | pc32_type, .addend = 0 },99        .{ .offset = 40, .info = (@as(u64, 3) << 32) | pc32_type, .addend = 0 },100    };101102    var cursor = Cursor.init(&relocations);103    const first = cursor.window(0, 32).?;104    try std.testing.expectEqual(@as(usize, 2), first.len);105    const second = cursor.window(32, 64).?;106    try std.testing.expectEqual(@as(usize, 1), second.len);107    try std.testing.expectEqual(@as(u32, 3), second[0].symbolIndex());108}109110test "eh frame relocation cursor falls back on unsorted input" {111    const pc32_type: u32 = @backingInt(std.elf.R_X86_64.PC32);112    const relocations = [_]Rela{113        .{ .offset = 40, .info = (@as(u64, 1) << 32) | pc32_type, .addend = 0 },114        .{ .offset = 8, .info = (@as(u64, 2) << 32) | pc32_type, .addend = 0 },115    };116117    var cursor = Cursor.init(&relocations);118    try std.testing.expect(!cursor.sorted);119    try std.testing.expect(cursor.window(0, 64) == null);120    try std.testing.expectEqual(@as(u32, 2), cursor.at(8).?.symbolIndex());121    try std.testing.expectEqual(@as(u32, 1), cursor.at(40).?.symbolIndex());122}

1pub const record = @import("record.zig");