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macho: assign and cache section ordinals upon creation

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then, when sorting sections within segments, clear and redo the
ordinals since we re-apply them to symbols anyway. It is vital
to have the ordinals consistent with parsing and resolving relocs
however.
This commit is contained in:
Jakub Konka 2021-07-22 22:19:15 +02:00
parent 4fd0cb7618
commit a4feb97cdf
3 changed files with 88 additions and 39 deletions
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117
src/link/MachO.zig
View File

@ -167,6 +167,9 @@ strtab_needs_relocation: bool = false,
has_dices: bool = false,
has_stabs: bool = false,
section_ordinals: std.ArrayListUnmanaged(MatchingSection) = .{},
section_to_ordinal: std.AutoHashMapUnmanaged(MatchingSection, u8) = .{},
pending_updates: std.ArrayListUnmanaged(struct {
kind: enum {
got,
@ -925,6 +928,13 @@ fn linkWithZld(self: *MachO, comp: *Compilation) !void {
else => unreachable,
};
// Initialize section ordinals with null ordinal pointing at
// PAGEZERO segment.
try self.section_ordinals.append(self.base.allocator, .{
.seg = 0,
.sect = 0,
});
try self.populateMetadata();
try self.parseInputFiles(positionals.items, self.base.options.sysroot);
try self.parseLibs(libs.items, self.base.options.sysroot);
@ -1482,6 +1492,10 @@ pub fn getMatchingSection(self: *MachO, sect: macho.section_64) !?MatchingSectio
}
};
if (res) |match| {
try self.createSectionOrdinal(match);
}
return res;
}
@ -1606,6 +1620,38 @@ fn sortSections(self: *MachO) !void {
self.blocks.deinit(self.base.allocator);
self.blocks = transient;
}
{
// Create new section ordinals.
self.section_ordinals.clearRetainingCapacity();
self.section_to_ordinal.clearRetainingCapacity();
// First ordinal is always null
self.section_ordinals.appendAssumeCapacity(.{
.seg = 0,
.sect = 0,
});
const text_seg = self.load_commands.items[self.text_segment_cmd_index.?].Segment;
for (text_seg.sections.items) |_, sect_id| {
try self.createSectionOrdinal(.{
.seg = self.text_segment_cmd_index.?,
.sect = @intCast(u16, sect_id),
});
}
const data_const_seg = self.load_commands.items[self.data_const_segment_cmd_index.?].Segment;
for (data_const_seg.sections.items) |_, sect_id| {
try self.createSectionOrdinal(.{
.seg = self.data_const_segment_cmd_index.?,
.sect = @intCast(u16, sect_id),
});
}
const data_seg = self.load_commands.items[self.data_segment_cmd_index.?].Segment;
for (data_seg.sections.items) |_, sect_id| {
try self.createSectionOrdinal(.{
.seg = self.data_segment_cmd_index.?,
.sect = @intCast(u16, sect_id),
});
}
}
}
fn allocateTextSegment(self: *MachO) !void {
@ -1732,7 +1778,7 @@ fn allocateTextBlocks(self: *MachO) !void {
const sect = seg.sections.items[match.sect];
var base_addr: u64 = sect.addr;
const n_sect = self.sectionId(match);
const n_sect = self.section_to_ordinal.get(match) orelse unreachable;
log.debug(" within section {s},{s}", .{ commands.segmentName(sect), commands.sectionName(sect) });
log.debug(" {}", .{sect});
@ -2260,6 +2306,7 @@ fn resolveSymbols(self: *MachO) !void {
.sect = self.common_section_index.?,
};
};
try self.createSectionOrdinal(match);
const size = sym.n_value;
const code = try self.base.allocator.alloc(u8, size);
@ -2272,7 +2319,7 @@ fn resolveSymbols(self: *MachO) !void {
var nlist = macho.nlist_64{
.n_strx = sym.n_strx,
.n_type = macho.N_SECT,
.n_sect = self.sectionId(match),
.n_sect = self.section_to_ordinal.get(match) orelse unreachable,
.n_desc = 0,
.n_value = 0,
};
@ -2402,7 +2449,7 @@ fn resolveSymbols(self: *MachO) !void {
var nlist = macho.nlist_64{
.n_strx = undef.n_strx,
.n_type = macho.N_SECT,
.n_sect = self.sectionId(match),
.n_sect = self.section_to_ordinal.get(match) orelse unreachable,
.n_desc = 0,
.n_value = 0,
};
@ -2498,6 +2545,10 @@ fn populateMetadata(self: *MachO) !void {
.@"align" = alignment,
.flags = macho.S_REGULAR | macho.S_ATTR_PURE_INSTRUCTIONS | macho.S_ATTR_SOME_INSTRUCTIONS,
});
try self.createSectionOrdinal(.{
.seg = self.text_segment_cmd_index.?,
.sect = self.text_section_index.?,
});
}
if (self.stubs_section_index == null) {
@ -2518,6 +2569,10 @@ fn populateMetadata(self: *MachO) !void {
.flags = macho.S_SYMBOL_STUBS | macho.S_ATTR_PURE_INSTRUCTIONS | macho.S_ATTR_SOME_INSTRUCTIONS,
.reserved2 = stub_size,
});
try self.createSectionOrdinal(.{
.seg = self.text_segment_cmd_index.?,
.sect = self.stubs_section_index.?,
});
}
if (self.stub_helper_section_index == null) {
@ -2538,6 +2593,10 @@ fn populateMetadata(self: *MachO) !void {
.@"align" = alignment,
.flags = macho.S_REGULAR | macho.S_ATTR_PURE_INSTRUCTIONS | macho.S_ATTR_SOME_INSTRUCTIONS,
});
try self.createSectionOrdinal(.{
.seg = self.text_segment_cmd_index.?,
.sect = self.stub_helper_section_index.?,
});
}
if (self.data_const_segment_cmd_index == null) {
@ -2557,6 +2616,10 @@ fn populateMetadata(self: *MachO) !void {
.@"align" = 3, // 2^3 = @sizeOf(u64)
.flags = macho.S_NON_LAZY_SYMBOL_POINTERS,
});
try self.createSectionOrdinal(.{
.seg = self.data_const_segment_cmd_index.?,
.sect = self.got_section_index.?,
});
}
if (self.data_segment_cmd_index == null) {
@ -2576,6 +2639,10 @@ fn populateMetadata(self: *MachO) !void {
.@"align" = 3, // 2^3 = @sizeOf(u64)
.flags = macho.S_LAZY_SYMBOL_POINTERS,
});
try self.createSectionOrdinal(.{
.seg = self.data_segment_cmd_index.?,
.sect = self.la_symbol_ptr_section_index.?,
});
}
if (self.data_section_index == null) {
@ -2584,6 +2651,10 @@ fn populateMetadata(self: *MachO) !void {
try data_seg.addSection(self.base.allocator, "__data", .{
.@"align" = 3, // 2^3 = @sizeOf(u64)
});
try self.createSectionOrdinal(.{
.seg = self.data_segment_cmd_index.?,
.sect = self.data_section_index.?,
});
}
if (self.linkedit_segment_cmd_index == null) {
@ -3290,6 +3361,8 @@ pub fn deinit(self: *MachO) void {
ds.deinit(self.base.allocator);
}
self.section_ordinals.deinit(self.base.allocator);
self.section_to_ordinal.deinit(self.base.allocator);
self.pending_updates.deinit(self.base.allocator);
self.got_entries.deinit(self.base.allocator);
self.got_entries_map.deinit(self.base.allocator);
@ -5816,37 +5889,6 @@ pub fn symbolIsTemp(sym: macho.nlist_64, sym_name: []const u8) bool {
return mem.startsWith(u8, sym_name, "l") or mem.startsWith(u8, sym_name, "L");
}
pub fn sectionId(self: MachO, match: MatchingSection) u8 {
// TODO there might be a more generic way of doing this.
var section: u8 = 0;
for (self.load_commands.items) |cmd, cmd_id| {
if (cmd != .Segment) break;
if (cmd_id == match.seg) {
section += @intCast(u8, match.sect) + 1;
break;
}
section += @intCast(u8, cmd.Segment.sections.items.len);
}
return section;
}
pub fn unpackSectionId(self: MachO, section_id: u8) MatchingSection {
var match: MatchingSection = undefined;
var section: u8 = 0;
outer: for (self.load_commands.items) |cmd, cmd_id| {
assert(cmd == .Segment);
for (cmd.Segment.sections.items) |_, sect_id| {
section += 1;
if (section_id == section) {
match.seg = @intCast(u16, cmd_id);
match.sect = @intCast(u16, sect_id);
break :outer;
}
}
}
return match;
}
fn packDylibOrdinal(ordinal: u16) u16 {
return ordinal * macho.N_SYMBOL_RESOLVER;
}
@ -5867,3 +5909,10 @@ pub fn findFirst(comptime T: type, haystack: []T, start: usize, predicate: anyty
}
return i;
}
fn createSectionOrdinal(self: *MachO, match: MatchingSection) !void {
if (self.section_to_ordinal.contains(match)) return;
const ordinal = @intCast(u8, self.section_ordinals.items.len);
try self.section_ordinals.append(self.base.allocator, match);
try self.section_to_ordinal.putNoClobber(self.base.allocator, match, ordinal);
}

4
src/link/MachO/Object.zig
View File

@ -733,7 +733,7 @@ pub fn parseTextBlocks(self: *Object, macho_file: *MachO) !void {
try macho_file.locals.append(macho_file.base.allocator, .{
.n_strx = try macho_file.makeString(sym_name),
.n_type = macho.N_SECT,
.n_sect = macho_file.sectionId(match),
.n_sect = macho_file.section_to_ordinal.get(match) orelse unreachable,
.n_desc = 0,
.n_value = sect.addr,
});
@ -779,7 +779,7 @@ pub fn parseTextBlocks(self: *Object, macho_file: *MachO) !void {
const nlist = nlist_with_index.nlist;
const local_sym_index = self.symbol_mapping.get(nlist_with_index.index) orelse unreachable;
const local = &macho_file.locals.items[local_sym_index];
local.n_sect = macho_file.sectionId(match);
local.n_sect = macho_file.section_to_ordinal.get(match) orelse unreachable;
const stab: ?TextBlock.Stab = if (self.debug_info) |di| blk: {
// TODO there has to be a better to handle this.

6
src/link/MachO/TextBlock.zig
View File

@ -620,7 +620,7 @@ fn initRelocFromObject(rel: macho.relocation_info, object: *Object, ctx: RelocCo
try ctx.macho_file.locals.append(ctx.macho_file.base.allocator, .{
.n_strx = try ctx.macho_file.makeString(sym_name),
.n_type = macho.N_SECT,
.n_sect = ctx.macho_file.sectionId(match),
.n_sect = ctx.macho_file.section_to_ordinal.get(match) orelse unreachable,
.n_desc = 0,
.n_value = sect.addr,
});
@ -832,7 +832,7 @@ pub fn parseRelocsFromObject(
},
.local => {
const source_sym = ctx.macho_file.locals.items[self.local_sym_index];
const match = ctx.macho_file.unpackSectionId(source_sym.n_sect);
const match = ctx.macho_file.section_ordinals.items[source_sym.n_sect];
const seg = ctx.macho_file.load_commands.items[match.seg].Segment;
const sect = seg.sections.items[match.sect];
const sect_type = commands.sectionType(sect);
@ -1096,7 +1096,7 @@ pub fn resolveRelocs(self: *TextBlock, macho_file: *MachO) !void {
const sym = macho_file.locals.items[rel.where_index];
const is_tlv = is_tlv: {
const source_sym = macho_file.locals.items[self.local_sym_index];
const match = macho_file.unpackSectionId(source_sym.n_sect);
const match = macho_file.section_ordinals.items[source_sym.n_sect];
const seg = macho_file.load_commands.items[match.seg].Segment;
const sect = seg.sections.items[match.sect];
break :is_tlv commands.sectionType(sect) == macho.S_THREAD_LOCAL_VARIABLES;