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pub fn gcAtoms(elf_file: *Elf) !void {
const comp = elf_file.base.comp;
const gpa = comp.gpa;
var roots = std.array_list.Managed(*Atom).init(gpa);
defer roots.deinit();
try collectRoots(&roots, elf_file);
mark(roots, elf_file);
prune(elf_file);
}
fn collectRoots(roots: *std.array_list.Managed(*Atom), elf_file: *Elf) !void {
if (elf_file.linkerDefinedPtr()) |obj| {
if (obj.entrySymbol(elf_file)) |sym| {
try markSymbol(sym, roots, elf_file);
}
}
if (elf_file.zigObjectPtr()) |zo| {
for (0..zo.global_symbols.items.len) |i| {
const ref = zo.resolveSymbol(@intCast(i | ZigObject.global_symbol_bit), elf_file);
const sym = elf_file.symbol(ref) orelse continue;
if (sym.file(elf_file).?.index() != zo.index) continue;
if (sym.flags.@"export") {
try markSymbol(sym, roots, elf_file);
}
}
}
for (elf_file.objects.items) |index| {
const object = elf_file.file(index).?.object;
for (0..object.globals().len) |i| {
const ref = object.resolveSymbol(@intCast(i), elf_file);
const sym = elf_file.symbol(ref) orelse continue;
if (sym.file(elf_file).?.index() != object.index) continue;
if (sym.flags.@"export") {
try markSymbol(sym, roots, elf_file);
}
}
}
const atomRoots = struct {
fn atomRoots(file: File, rs: anytype, ef: *Elf) !void {
for (file.atoms()) |atom_index| {
const atom = file.atom(atom_index) orelse continue;
if (!atom.alive) continue;
const shdr = atom.inputShdr(ef);
const name = atom.name(ef);
const is_gc_root = blk: {
if (shdr.sh_flags & elf.SHF_GNU_RETAIN != 0) break :blk true;
if (shdr.sh_type == elf.SHT_NOTE) break :blk true;
if (shdr.sh_type == elf.SHT_PREINIT_ARRAY) break :blk true;
if (shdr.sh_type == elf.SHT_INIT_ARRAY) break :blk true;
if (shdr.sh_type == elf.SHT_FINI_ARRAY) break :blk true;
if (mem.startsWith(u8, name, ".ctors")) break :blk true;
if (mem.startsWith(u8, name, ".dtors")) break :blk true;
if (mem.startsWith(u8, name, ".init")) break :blk true;
if (mem.startsWith(u8, name, ".fini")) break :blk true;
if (Elf.isCIdentifier(name)) break :blk true;
break :blk false;
};
if (is_gc_root and markAtom(atom)) try rs.append(atom);
if (shdr.sh_flags & elf.SHF_ALLOC == 0) atom.visited = true;
}
// Mark every atom referenced by CIE as alive.
for (file.cies()) |cie| {
for (cie.relocs(ef)) |rel| {
const ref = file.resolveSymbol(rel.r_sym(), ef);
const sym = ef.symbol(ref) orelse continue;
try markSymbol(sym, rs, ef);
}
}
}
}.atomRoots;
if (elf_file.zigObjectPtr()) |zo| {
try atomRoots(zo.asFile(), roots, elf_file);
}
for (elf_file.objects.items) |index| {
try atomRoots(elf_file.file(index).?, roots, elf_file);
}
}
fn markSymbol(sym: *Symbol, roots: *std.array_list.Managed(*Atom), elf_file: *Elf) !void {
if (sym.mergeSubsection(elf_file)) |msub| {
msub.alive = true;
return;
}
const atom = sym.atom(elf_file) orelse return;
if (markAtom(atom)) try roots.append(atom);
}
fn markAtom(atom: *Atom) bool {
const already_visited = atom.visited;
atom.visited = true;
return atom.alive and !already_visited;
}
fn markLive(atom: *Atom, elf_file: *Elf) void {
if (@import("build_options").enable_logging) track_live_level.incr();
assert(atom.visited);
const file = atom.file(elf_file).?;
switch (file) {
.object => |object| {
for (atom.fdes(object)) |fde| {
for (fde.relocs(object)[1..]) |rel| {
const ref = file.resolveSymbol(rel.r_sym(), elf_file);
const target_sym = elf_file.symbol(ref) orelse continue;
const target_atom = target_sym.atom(elf_file) orelse continue;
target_atom.alive = true;
gc_track_live_log.debug("{f}marking live atom({d})", .{ track_live_level, target_atom.atom_index });
if (markAtom(target_atom)) markLive(target_atom, elf_file);
}
}
},
else => {},
}
for (atom.relocs(elf_file)) |rel| {
const ref = file.resolveSymbol(rel.r_sym(), elf_file);
const target_sym = elf_file.symbol(ref) orelse continue;
if (target_sym.mergeSubsection(elf_file)) |msub| {
msub.alive = true;
continue;
}
const target_atom = target_sym.atom(elf_file) orelse continue;
target_atom.alive = true;
gc_track_live_log.debug("{f}marking live atom({d})", .{ track_live_level, target_atom.atom_index });
if (markAtom(target_atom)) markLive(target_atom, elf_file);
}
}
fn mark(roots: std.array_list.Managed(*Atom), elf_file: *Elf) void {
for (roots.items) |root| {
gc_track_live_log.debug("root atom({d})", .{root.atom_index});
markLive(root, elf_file);
}
}
fn pruneInFile(file: File) void {
for (file.atoms()) |atom_index| {
const atom = file.atom(atom_index) orelse continue;
if (atom.alive and !atom.visited) {
atom.alive = false;
switch (file) {
.object => |object| atom.markFdesDead(object),
else => {},
}
}
}
}
fn prune(elf_file: *Elf) void {
if (elf_file.zigObjectPtr()) |zo| {
pruneInFile(zo.asFile());
}
for (elf_file.objects.items) |index| {
pruneInFile(elf_file.file(index).?);
}
}
const Level = struct {
value: usize = 0,
fn incr(self: *@This()) void {
self.value += 1;
}
pub fn format(self: *const @This(), w: *std.Io.Writer) std.Io.Writer.Error!void {
try w.splatByteAll(' ', self.value);
}
};
var track_live_level: Level = .{};
const std = @import("std");
const assert = std.debug.assert;
const elf = std.elf;
const gc_track_live_log = std.log.scoped(.gc_track_live);
const mem = std.mem;
const Allocator = mem.Allocator;
const Atom = @import("Atom.zig");
const Elf = @import("../Elf.zig");
const File = @import("file.zig").File;
const Symbol = @import("Symbol.zig");
const ZigObject = @import("ZigObject.zig");
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