authorgravatar for kubkon@jakubkonka.comJakub Konka <kubkon@jakubkonka.com> 2023-11-01 10:26:38+01:00
committergravatar for kubkon@jakubkonka.comJakub Konka <kubkon@jakubkonka.com> 2023-11-04 09:08:27+01:00
logb8c8565e93d3625e5eb46a3f64a461f86b8d8eb4
tree1e40889825b691397d0aed0e7349044b26fa41dc
parent25c53f08a6add493043a407ce15bc727dc33356d

elf: implement --gc-sections for non-LLVM Zig source

3 files changed, 157 insertions(+), 22 deletions(-)

src/link/Elf/file.zig+16
......@@ -99,6 +99,21 @@ pub const File = union(enum) {
9999 };
100100 }
101101
102 pub fn cies(file: File) []const Cie {
103 return switch (file) {
104 .zig_object => &[0]Cie{},
105 .object => |x| x.cies.items,
106 inline else => unreachable,
107 };
108 }
109
110 pub fn symbol(file: File, ind: Symbol.Index) Symbol.Index {
111 return switch (file) {
112 .zig_object => |x| x.symbol(ind),
113 inline else => |x| x.symbols.items[ind],
114 };
115 }
116
102117 pub fn locals(file: File) []const Symbol.Index {
103118 return switch (file) {
104119 .linker_defined, .shared_object => &[0]Symbol.Index{},
......@@ -196,6 +211,7 @@ const elf = std.elf;
196211
197212const Allocator = std.mem.Allocator;
198213const Atom = @import("Atom.zig");
214const Cie = @import("eh_frame.zig").Cie;
199215const Elf = @import("../Elf.zig");
200216const LinkerDefined = @import("LinkerDefined.zig");
201217const Object = @import("Object.zig");
src/link/Elf/gc.zig+26-17
......@@ -1,19 +1,27 @@
11pub fn gcAtoms(elf_file: *Elf) !void {
2 var roots = std.ArrayList(*Atom).init(elf_file.base.allocator);
2 const gpa = elf_file.base.allocator;
3 const num_files = elf_file.objects.items.len + @intFromBool(elf_file.zig_object_index != null);
4 var files = try std.ArrayList(File.Index).initCapacity(gpa, num_files);
5 defer files.deinit();
6 if (elf_file.zig_object_index) |index| files.appendAssumeCapacity(index);
7 for (elf_file.objects.items) |index| files.appendAssumeCapacity(index);
8
9 var roots = std.ArrayList(*Atom).init(gpa);
310 defer roots.deinit();
4 try collectRoots(&roots, elf_file);
11 try collectRoots(&roots, files.items, elf_file);
12
513 mark(roots, elf_file);
6 prune(elf_file);
14 prune(files.items, elf_file);
715}
816
9fn collectRoots(roots: *std.ArrayList(*Atom), elf_file: *Elf) !void {
17fn collectRoots(roots: *std.ArrayList(*Atom), files: []const File.Index, elf_file: *Elf) !void {
1018 if (elf_file.entry_index) |index| {
1119 const global = elf_file.symbol(index);
1220 try markSymbol(global, roots, elf_file);
1321 }
1422
15 for (elf_file.objects.items) |index| {
16 for (elf_file.file(index).?.object.globals()) |global_index| {
23 for (files) |index| {
24 for (elf_file.file(index).?.globals()) |global_index| {
1725 const global = elf_file.symbol(global_index);
1826 if (global.file(elf_file)) |file| {
1927 if (file.index() == index and global.flags.@"export")
......@@ -22,10 +30,10 @@ fn collectRoots(roots: *std.ArrayList(*Atom), elf_file: *Elf) !void {
2230 }
2331 }
2432
25 for (elf_file.objects.items) |index| {
26 const object = elf_file.file(index).?.object;
33 for (files) |index| {
34 const file = elf_file.file(index).?;
2735
28 for (object.atoms.items) |atom_index| {
36 for (file.atoms()) |atom_index| {
2937 const atom = elf_file.atom(atom_index) orelse continue;
3038 if (!atom.flags.alive) continue;
3139
......@@ -49,9 +57,9 @@ fn collectRoots(roots: *std.ArrayList(*Atom), elf_file: *Elf) !void {
4957 }
5058
5159 // Mark every atom referenced by CIE as alive.
52 for (object.cies.items) |cie| {
60 for (file.cies()) |cie| {
5361 for (cie.relocs(elf_file)) |rel| {
54 const sym = elf_file.symbol(object.symbols.items[rel.r_sym()]);
62 const sym = elf_file.symbol(file.symbol(rel.r_sym()));
5563 try markSymbol(sym, roots, elf_file);
5664 }
5765 }
......@@ -73,11 +81,11 @@ fn markLive(atom: *Atom, elf_file: *Elf) void {
7381 if (@import("build_options").enable_logging) track_live_level.incr();
7482
7583 assert(atom.flags.visited);
76 const object = atom.file(elf_file).?.object;
84 const file = atom.file(elf_file).?;
7785
7886 for (atom.fdes(elf_file)) |fde| {
7987 for (fde.relocs(elf_file)[1..]) |rel| {
80 const target_sym = elf_file.symbol(object.symbols.items[rel.r_sym()]);
88 const target_sym = elf_file.symbol(file.symbol(rel.r_sym()));
8189 const target_atom = target_sym.atom(elf_file) orelse continue;
8290 target_atom.flags.alive = true;
8391 gc_track_live_log.debug("{}marking live atom({d})", .{ track_live_level, target_atom.atom_index });
......@@ -86,7 +94,7 @@ fn markLive(atom: *Atom, elf_file: *Elf) void {
8694 }
8795
8896 for (atom.relocs(elf_file)) |rel| {
89 const target_sym = elf_file.symbol(object.symbols.items[rel.r_sym()]);
97 const target_sym = elf_file.symbol(file.symbol(rel.r_sym()));
9098 const target_atom = target_sym.atom(elf_file) orelse continue;
9199 target_atom.flags.alive = true;
92100 gc_track_live_log.debug("{}marking live atom({d})", .{ track_live_level, target_atom.atom_index });
......@@ -101,9 +109,9 @@ fn mark(roots: std.ArrayList(*Atom), elf_file: *Elf) void {
101109 }
102110}
103111
104fn prune(elf_file: *Elf) void {
105 for (elf_file.objects.items) |index| {
106 for (elf_file.file(index).?.object.atoms.items) |atom_index| {
112fn prune(files: []const File.Index, elf_file: *Elf) void {
113 for (files) |index| {
114 for (elf_file.file(index).?.atoms()) |atom_index| {
107115 const atom = elf_file.atom(atom_index) orelse continue;
108116 if (atom.flags.alive and !atom.flags.visited) {
109117 atom.flags.alive = false;
......@@ -158,4 +166,5 @@ const mem = std.mem;
158166const Allocator = mem.Allocator;
159167const Atom = @import("Atom.zig");
160168const Elf = @import("../Elf.zig");
169const File = @import("file.zig").File;
161170const Symbol = @import("Symbol.zig");
test/link/elf.zig+115-5
......@@ -6,9 +6,13 @@ pub fn build(b: *Build) void {
66 const elf_step = b.step("test-elf", "Run ELF tests");
77 b.default_step = elf_step;
88
9 const musl_target = CrossTarget{
9 const default_target = CrossTarget{
1010 .cpu_arch = .x86_64, // TODO relax this once ELF linker is able to handle other archs
1111 .os_tag = .linux,
12 };
13 const musl_target = CrossTarget{
14 .cpu_arch = .x86_64,
15 .os_tag = .linux,
1216 .abi = .musl,
1317 };
1418 const glibc_target = CrossTarget{
......@@ -18,7 +22,8 @@ pub fn build(b: *Build) void {
1822 };
1923
2024 // Exercise linker with self-hosted backend (no LLVM)
21 elf_step.dependOn(testLinkingZig(b, .{ .use_llvm = false }));
25 elf_step.dependOn(testGcSectionsZig(b, .{ .use_llvm = false, .target = default_target }));
26 elf_step.dependOn(testLinkingZig(b, .{ .use_llvm = false, .target = default_target }));
2227 elf_step.dependOn(testImportingDataDynamic(b, .{ .use_llvm = false, .target = glibc_target }));
2328 elf_step.dependOn(testImportingDataStatic(b, .{ .use_llvm = false, .target = musl_target }));
2429
......@@ -876,6 +881,110 @@ fn testGcSections(b: *Build, opts: Options) *Step {
876881 return test_step;
877882}
878883
884fn testGcSectionsZig(b: *Build, opts: Options) *Step {
885 const test_step = addTestStep(b, "gc-sections-zig", opts);
886
887 const obj = addObject(b, "obj", .{
888 .target = opts.target,
889 .use_llvm = true,
890 .use_lld = true,
891 });
892 addCSourceBytes(obj,
893 \\int live_var1 = 1;
894 \\int live_var2 = 2;
895 \\int dead_var1 = 3;
896 \\int dead_var2 = 4;
897 \\void live_fn1() {}
898 \\void live_fn2() { live_fn1(); }
899 \\void dead_fn1() {}
900 \\void dead_fn2() { dead_fn1(); }
901 , &.{});
902 obj.link_function_sections = true;
903 obj.link_data_sections = true;
904
905 {
906 const exe = addExecutable(b, "test1", opts);
907 addZigSourceBytes(exe,
908 \\const std = @import("std");
909 \\extern var live_var1: i32;
910 \\extern var live_var2: i32;
911 \\extern fn live_fn2() void;
912 \\pub fn main() void {
913 \\ const stdout = std.io.getStdOut();
914 \\ stdout.writer().print("{d} {d}\n", .{ live_var1, live_var2 }) catch unreachable;
915 \\ live_fn2();
916 \\}
917 );
918 exe.addObject(obj);
919 exe.link_gc_sections = false;
920
921 const run = addRunArtifact(exe);
922 run.expectStdOutEqual("1 2\n");
923 test_step.dependOn(&run.step);
924
925 const check = exe.checkObject();
926 check.checkInSymtab();
927 check.checkContains("live_var1");
928 check.checkInSymtab();
929 check.checkContains("live_var2");
930 check.checkInSymtab();
931 check.checkContains("dead_var1");
932 check.checkInSymtab();
933 check.checkContains("dead_var2");
934 check.checkInSymtab();
935 check.checkContains("live_fn1");
936 check.checkInSymtab();
937 check.checkContains("live_fn2");
938 check.checkInSymtab();
939 check.checkContains("dead_fn1");
940 check.checkInSymtab();
941 check.checkContains("dead_fn2");
942 test_step.dependOn(&check.step);
943 }
944
945 {
946 const exe = addExecutable(b, "test2", opts);
947 addZigSourceBytes(exe,
948 \\const std = @import("std");
949 \\extern var live_var1: i32;
950 \\extern var live_var2: i32;
951 \\extern fn live_fn2() void;
952 \\pub fn main() void {
953 \\ const stdout = std.io.getStdOut();
954 \\ stdout.writer().print("{d} {d}\n", .{ live_var1, live_var2 }) catch unreachable;
955 \\ live_fn2();
956 \\}
957 );
958 exe.addObject(obj);
959 exe.link_gc_sections = true;
960
961 const run = addRunArtifact(exe);
962 run.expectStdOutEqual("1 2\n");
963 test_step.dependOn(&run.step);
964
965 const check = exe.checkObject();
966 check.checkInSymtab();
967 check.checkContains("live_var1");
968 check.checkInSymtab();
969 check.checkContains("live_var2");
970 check.checkInSymtab();
971 check.checkNotPresent("dead_var1");
972 check.checkInSymtab();
973 check.checkNotPresent("dead_var2");
974 check.checkInSymtab();
975 check.checkContains("live_fn1");
976 check.checkInSymtab();
977 check.checkContains("live_fn2");
978 check.checkInSymtab();
979 check.checkNotPresent("dead_fn1");
980 check.checkInSymtab();
981 check.checkNotPresent("dead_fn2");
982 test_step.dependOn(&check.step);
983 }
984
985 return test_step;
986}
987
879988fn testHiddenWeakUndef(b: *Build, opts: Options) *Step {
880989 const test_step = addTestStep(b, "hidden-weak-undef", opts);
881990
......@@ -3114,6 +3223,7 @@ const Options = struct {
31143223 target: CrossTarget = .{ .cpu_arch = .x86_64, .os_tag = .linux },
31153224 optimize: std.builtin.OptimizeMode = .Debug,
31163225 use_llvm: bool = true,
3226 use_lld: bool = false,
31173227};
31183228
31193229fn addTestStep(b: *Build, comptime prefix: []const u8, opts: Options) *Step {
......@@ -3134,7 +3244,7 @@ fn addExecutable(b: *Build, name: []const u8, opts: Options) *Compile {
31343244 .target = opts.target,
31353245 .optimize = opts.optimize,
31363246 .use_llvm = opts.use_llvm,
3137 .use_lld = false,
3247 .use_lld = opts.use_lld,
31383248 });
31393249}
31403250
......@@ -3144,7 +3254,7 @@ fn addObject(b: *Build, name: []const u8, opts: Options) *Compile {
31443254 .target = opts.target,
31453255 .optimize = opts.optimize,
31463256 .use_llvm = opts.use_llvm,
3147 .use_lld = false,
3257 .use_lld = opts.use_lld,
31483258 });
31493259}
31503260
......@@ -3164,7 +3274,7 @@ fn addSharedLibrary(b: *Build, name: []const u8, opts: Options) *Compile {
31643274 .target = opts.target,
31653275 .optimize = opts.optimize,
31663276 .use_llvm = opts.use_llvm,
3167 .use_lld = false,
3277 .use_lld = opts.use_lld,
31683278 });
31693279}
31703280