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Merge pull request ziglang#17955 from ziglang/issue-17951
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macho: handle special section/segment boundary symbols
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@kubkon
kubkon authored Nov 10, 2023
2 parents ec934c6 + 1717772 commit 9ad03b6
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Showing 6 changed files with 398 additions and 114 deletions.
170 changes: 164 additions & 6 deletions src/link/MachO.zig
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Original file line number Diff line number Diff line change
Expand Up @@ -251,7 +251,7 @@ pub fn createEmpty(gpa: Allocator, options: link.Options) !*MachO {
.incremental,
};

if (options.use_llvm) {
if (options.use_llvm and options.module != null) {
self.llvm_object = try LlvmObject.create(gpa, options);
}

Expand Down Expand Up @@ -1416,6 +1416,51 @@ pub fn allocateSpecialSymbols(self: *MachO) !void {
seg.segName(),
});
}

for (self.globals.items) |global| {
const sym = self.getSymbolPtr(global);
if (sym.n_desc != N_BOUNDARY) continue;
if (self.getSectionBoundarySymbol(global)) |bsym| {
const sect_id = self.getSectionByName(bsym.segname, bsym.sectname) orelse {
try self.reportUnresolvedBoundarySymbol(self.getSymbolName(global), "section not found: {s},{s}", .{
bsym.segname, bsym.sectname,
});
continue;
};
const sect = self.sections.items(.header)[sect_id];
sym.n_sect = sect_id + 1;
sym.n_value = switch (bsym.kind) {
.start => sect.addr,
.stop => sect.addr + sect.size,
};

log.debug("allocating {s} at @0x{x} sect({d})", .{
self.getSymbolName(global),
sym.n_value,
sym.n_sect,
});

continue;
}
if (self.getSegmentBoundarySymbol(global)) |bsym| {
const seg_id = self.getSegmentByName(bsym.segname) orelse {
try self.reportUnresolvedBoundarySymbol(self.getSymbolName(global), "segment not found: {s}", .{
bsym.segname,
});

continue;
};
const seg = self.segments.items[seg_id];
sym.n_value = switch (bsym.kind) {
.start => seg.vmaddr,
.stop => seg.vmaddr + seg.vmsize,
};

log.debug("allocating {s} at @0x{x} ", .{ self.getSymbolName(global), sym.n_value });

continue;
}
}
}

const CreateAtomOpts = struct {
Expand All @@ -1442,6 +1487,7 @@ pub fn createTentativeDefAtoms(self: *MachO) !void {
const sym = self.getSymbolPtr(global);
if (!sym.tentative()) continue;
if (sym.n_desc == N_DEAD) continue;
if (sym.n_desc == N_BOUNDARY) continue;

log.debug("creating tentative definition for ATOM(%{d}, '{s}') in object({?})", .{
global.sym_index, self.getSymbolName(global), global.file,
Expand Down Expand Up @@ -1630,6 +1676,13 @@ pub fn resolveSymbols(self: *MachO) !void {
try self.createMhExecuteHeaderSymbol();
try self.createDsoHandleSymbol();
try self.resolveSymbolsAtLoading();

// Final stop, check if unresolved contain any of the special magic boundary symbols
// * section$start$
// * section$stop$
// * segment$start$
// * segment$stop$
try self.resolveBoundarySymbols();
}

fn resolveGlobalSymbol(self: *MachO, current: SymbolWithLoc) !void {
Expand Down Expand Up @@ -1845,6 +1898,34 @@ fn resolveSymbolsAtLoading(self: *MachO) !void {
}
}

fn resolveBoundarySymbols(self: *MachO) !void {
var next_sym: usize = 0;
while (next_sym < self.unresolved.count()) {
const global_index = self.unresolved.keys()[next_sym];
const global = &self.globals.items[global_index];

if (self.getSectionBoundarySymbol(global.*) != null or self.getSegmentBoundarySymbol(global.*) != null) {
const sym_index = try self.allocateSymbol();
const sym_loc = SymbolWithLoc{ .sym_index = sym_index };
const sym = self.getSymbolPtr(sym_loc);
sym.* = .{
.n_strx = try self.strtab.insert(self.base.allocator, self.getSymbolName(global.*)),
.n_type = macho.N_SECT | macho.N_EXT,
.n_sect = 0,
.n_desc = N_BOUNDARY,
.n_value = 0,
};
if (global.getFile()) |file| {
const global_object = &self.objects.items[file];
global_object.globals_lookup[global.sym_index] = global_index;
}
global.* = sym_loc;
_ = self.unresolved.swapRemove(global_index);
continue;
}
}
}

pub fn deinit(self: *MachO) void {
const gpa = self.base.allocator;

Expand Down Expand Up @@ -3565,6 +3646,7 @@ fn collectRebaseData(self: *MachO, rebase: *Rebase) !void {
const atom = self.getAtom(atom_index);
const sym = self.getSymbol(atom.getSymbolWithLoc());
if (sym.n_desc == N_DEAD) continue;
if (sym.n_desc == N_BOUNDARY) continue;

const sect_id = sym.n_sect - 1;
const section = self.sections.items(.header)[sect_id];
Expand Down Expand Up @@ -3719,6 +3801,7 @@ fn collectBindData(self: *MachO, bind: anytype, raw_bindings: anytype) !void {
const atom = self.getAtom(atom_index);
const sym = self.getSymbol(atom.getSymbolWithLoc());
if (sym.n_desc == N_DEAD) continue;
if (sym.n_desc == N_BOUNDARY) continue;

const sect_id = sym.n_sect - 1;
const section = self.sections.items(.header)[sect_id];
Expand Down Expand Up @@ -3819,6 +3902,7 @@ fn collectExportData(self: *MachO, trie: *Trie) !void {
if (sym.undf()) continue;
assert(sym.ext());
if (sym.n_desc == N_DEAD) continue;
if (sym.n_desc == N_BOUNDARY) continue;

const sym_name = self.getSymbolName(global);
log.debug(" (putting '{s}' defined at 0x{x})", .{ sym_name, sym.n_value });
Expand Down Expand Up @@ -3953,7 +4037,8 @@ const asc_u64 = std.sort.asc(u64);
fn addSymbolToFunctionStarts(self: *MachO, sym_loc: SymbolWithLoc, addresses: *std.ArrayList(u64)) !void {
const sym = self.getSymbol(sym_loc);
if (sym.n_strx == 0) return;
if (sym.n_desc == MachO.N_DEAD) return;
if (sym.n_desc == N_DEAD) return;
if (sym.n_desc == N_BOUNDARY) return;
if (self.symbolIsTemp(sym_loc)) return;
try addresses.append(sym.n_value);
}
Expand Down Expand Up @@ -4061,7 +4146,8 @@ pub fn writeDataInCode(self: *MachO) !void {
for (object.exec_atoms.items) |atom_index| {
const atom = self.getAtom(atom_index);
const sym = self.getSymbol(atom.getSymbolWithLoc());
if (sym.n_desc == MachO.N_DEAD) continue;
if (sym.n_desc == N_DEAD) continue;
if (sym.n_desc == N_BOUNDARY) return;

const source_addr = if (object.getSourceSymbol(atom.sym_index)) |source_sym|
source_sym.n_value
Expand Down Expand Up @@ -4119,7 +4205,8 @@ fn writeSymtabs(self: *MachO) !void {
fn addLocalToSymtab(self: *MachO, sym_loc: SymbolWithLoc, locals: *std.ArrayList(macho.nlist_64)) !void {
const sym = self.getSymbol(sym_loc);
if (sym.n_strx == 0) return; // no name, skip
if (sym.n_desc == MachO.N_DEAD) return; // garbage-collected, skip
if (sym.n_desc == N_DEAD) return; // garbage-collected, skip
if (sym.n_desc == N_BOUNDARY) return; // boundary symbol, skip
if (sym.ext()) return; // an export lands in its own symtab section, skip
if (self.symbolIsTemp(sym_loc)) return; // local temp symbol, skip
var out_sym = sym;
Expand Down Expand Up @@ -4157,6 +4244,7 @@ fn writeSymtab(self: *MachO) !SymtabCtx {
const sym = self.getSymbol(global);
if (sym.undf()) continue; // import, skip
if (sym.n_desc == N_DEAD) continue;
if (sym.n_desc == N_BOUNDARY) continue;
var out_sym = sym;
out_sym.n_strx = try self.strtab.insert(gpa, self.getSymbolName(global));
try exports.append(out_sym);
Expand All @@ -4172,6 +4260,7 @@ fn writeSymtab(self: *MachO) !SymtabCtx {
if (sym.n_strx == 0) continue; // no name, skip
if (!sym.undf()) continue; // not an import, skip
if (sym.n_desc == N_DEAD) continue;
if (sym.n_desc == N_BOUNDARY) continue;
const new_index = @as(u32, @intCast(imports.items.len));
var out_sym = sym;
out_sym.n_strx = try self.strtab.insert(gpa, self.getSymbolName(global));
Expand Down Expand Up @@ -4842,6 +4931,55 @@ pub fn getSymbolName(self: *const MachO, sym_with_loc: SymbolWithLoc) []const u8
}
}

const BoundarySymbolKind = enum {
start,
stop,
};

const SectionBoundarySymbol = struct {
kind: BoundarySymbolKind,
segname: []const u8,
sectname: []const u8,
};

pub fn getSectionBoundarySymbol(self: *const MachO, sym_with_loc: SymbolWithLoc) ?SectionBoundarySymbol {
const sym_name = self.getSymbolName(sym_with_loc);
if (mem.startsWith(u8, sym_name, "section$")) {
const trailing = sym_name["section$".len..];
const kind: BoundarySymbolKind = kind: {
if (mem.startsWith(u8, trailing, "start$")) break :kind .start;
if (mem.startsWith(u8, trailing, "stop$")) break :kind .stop;
return null;
};
const names = trailing[@tagName(kind).len + 1 ..];
const sep_idx = mem.indexOf(u8, names, "$") orelse return null;
const segname = names[0..sep_idx];
const sectname = names[sep_idx + 1 ..];
return .{ .kind = kind, .segname = segname, .sectname = sectname };
}
return null;
}

const SegmentBoundarySymbol = struct {
kind: BoundarySymbolKind,
segname: []const u8,
};

pub fn getSegmentBoundarySymbol(self: *const MachO, sym_with_loc: SymbolWithLoc) ?SegmentBoundarySymbol {
const sym_name = self.getSymbolName(sym_with_loc);
if (mem.startsWith(u8, sym_name, "segment$")) {
const trailing = sym_name["segment$".len..];
const kind: BoundarySymbolKind = kind: {
if (mem.startsWith(u8, trailing, "start$")) break :kind .start;
if (mem.startsWith(u8, trailing, "stop$")) break :kind .stop;
return null;
};
const segname = trailing[@tagName(kind).len + 1 ..];
return .{ .kind = kind, .segname = segname };
}
return null;
}

/// Returns pointer to the global entry for `name` if one exists.
pub fn getGlobalPtr(self: *MachO, name: []const u8) ?*SymbolWithLoc {
const global_index = self.resolver.get(name) orelse return null;
Expand Down Expand Up @@ -5137,6 +5275,23 @@ pub fn reportParseError(
});
}

pub fn reportUnresolvedBoundarySymbol(
self: *MachO,
sym_name: []const u8,
comptime format: []const u8,
args: anytype,
) error{OutOfMemory}!void {
const gpa = self.base.allocator;
try self.misc_errors.ensureUnusedCapacity(gpa, 1);
var notes = try gpa.alloc(File.ErrorMsg, 1);
errdefer gpa.free(notes);
notes[0] = .{ .msg = try std.fmt.allocPrint(gpa, "while resolving {s}", .{sym_name}) };
self.misc_errors.appendAssumeCapacity(.{
.msg = try std.fmt.allocPrint(gpa, format, args),
.notes = notes,
});
}

pub fn reportUndefined(self: *MachO) error{OutOfMemory}!void {
const gpa = self.base.allocator;
const count = self.unresolved.count();
Expand Down Expand Up @@ -5340,7 +5495,8 @@ pub fn logSymtab(self: *MachO) void {
for (self.globals.items, 0..) |global, i| {
const sym = self.getSymbol(global);
if (sym.undf()) continue;
if (sym.n_desc == MachO.N_DEAD) continue;
if (sym.n_desc == N_DEAD) continue;
if (sym.n_desc == N_BOUNDARY) continue;
scoped_log.debug(" %{d}: {s} @{x} in sect({d}), {s} (def in object({?}))", .{
i,
self.getSymbolName(global),
Expand All @@ -5355,7 +5511,8 @@ pub fn logSymtab(self: *MachO) void {
for (self.globals.items, 0..) |global, i| {
const sym = self.getSymbol(global);
if (!sym.undf()) continue;
if (sym.n_desc == MachO.N_DEAD) continue;
if (sym.n_desc == N_DEAD) continue;
if (sym.n_desc == N_BOUNDARY) continue;
const ord = @divTrunc(sym.n_desc, macho.N_SYMBOL_RESOLVER);
scoped_log.debug(" %{d}: {s} @{x} in ord({d}), {s}", .{
i,
Expand Down Expand Up @@ -5466,6 +5623,7 @@ pub fn logAtom(self: *MachO, atom_index: Atom.Index, logger: anytype) void {

pub const base_tag: File.Tag = File.Tag.macho;
pub const N_DEAD: u16 = @as(u16, @bitCast(@as(i16, -1)));
pub const N_BOUNDARY: u16 = @as(u16, @bitCast(@as(i16, -2)));

/// Mode of operation of the linker.
pub const Mode = enum {
Expand Down
1 change: 1 addition & 0 deletions src/link/MachO/dead_strip.zig
View file
Original file line number Diff line number Diff line change
Expand Up @@ -50,6 +50,7 @@ fn collectRoots(macho_file: *MachO, roots: *AtomTable) !void {
for (macho_file.globals.items) |global| {
const sym = macho_file.getSymbol(global);
if (sym.undf()) continue;
if (sym.n_desc == MachO.N_BOUNDARY) continue;

if (global.getFile()) |file| {
try addRoot(macho_file, roots, file, global);
Expand Down
11 changes: 5 additions & 6 deletions test/link.zig
View file
Original file line number Diff line number Diff line change
Expand Up @@ -4,6 +4,11 @@ pub const Case = struct {
};

pub const cases = [_]Case{
.{
.build_root = "test/link",
.import = @import("link/link.zig"),
},

.{
.build_root = "test/link/bss",
.import = @import("link/bss/build.zig"),
Expand All @@ -29,12 +34,6 @@ pub const cases = [_]Case{
.import = @import("link/glibc_compat/build.zig"),
},

// Elf Cases
.{
.build_root = "test/link",
.import = @import("link/elf.zig"),
},

// WASM Cases
// https://github.com/ziglang/zig/issues/16938
//.{
Expand Down
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