elf: handle TLS LD model for executables

kubkon · Jul 18, 2023 · bf984a0 · bf984a0
1 parent b7e6513
commit bf984a0
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Showing 4 changed files with 64 additions and 4 deletions.
diff --git a/src/Elf.zig b/src/Elf.zig
@@ -2507,7 +2507,7 @@ pub inline fn getPltGotEntryAddress(self: *Elf, index: u32) u64 {
 }
 
 pub inline fn getTlsLdAddress(self: *Elf) u64 {
-    return self.getGotEntryAddress(@as(u32, @intCast(self.got.symbols.items.len)));
+    return self.getGotEntryAddress(self.got.getTlsLdIndex());
 }
 
 pub fn getTpAddress(self: *Elf) u64 {

diff --git a/src/Elf/Atom.zig b/src/Elf/Atom.zig
@@ -619,7 +619,8 @@ pub fn resolveRelocsAlloc(self: Atom, elf_file: *Elf, writer: anytype) !void {
 
             elf.R_X86_64_TLSLD => {
                 if (elf_file.got.emit_tlsld) {
-                    try cwriter.writeIntLittle(i32, @as(i32, @intCast(@as(i64, @intCast(elf_file.getTlsLdAddress())) + A - P)));
+                    const S_ = @as(i64, @intCast(elf_file.getTlsLdAddress()));
+                    try cwriter.writeIntLittle(i32, @as(i32, @intCast(S_ + A - P)));
                 } else {
                     try relaxTlsLdToLe(
                         relocs[i .. i + 2],

diff --git a/src/Elf/synthetic.zig b/src/Elf/synthetic.zig
@@ -653,13 +653,17 @@ pub const GotSection = struct {
         got.next_index += 2;
     }
 
+    pub inline fn getTlsLdIndex(got: GotSection) u32 {
+        return got.next_index;
+    }
+
     pub fn size(got: GotSection) usize {
         var s: usize = 0;
         for (got.symbols.items) |sym| switch (sym) {
             .got, .gottp => s += 8,
             .tlsgd, .tlsdesc => s += 16,
         };
-        if (got.emit_tlsld) s += 8;
+        if (got.emit_tlsld) s += 16;
         return s;
     }
 
@@ -720,6 +724,7 @@ pub const GotSection = struct {
         if (got.emit_tlsld) {
             if (is_shared) @panic("TODO");
             try writer.writeIntLittle(u64, 1); // TODO we assume executable output here
+            try writer.writeIntLittle(u64, 0);
         }
     }
 
@@ -912,7 +917,7 @@ pub const GotSection = struct {
                 .st_other = 0,
                 .st_shndx = elf_file.got_sect_index.?,
                 .st_value = elf_file.getTlsLdAddress(),
-                .st_size = @sizeOf(u64),
+                .st_size = 16,
             };
             ilocal += 1;
         }

diff --git a/test/elf.zig b/test/elf.zig
@@ -22,6 +22,7 @@ pub fn addElfTests(b: *Build, opts: Options) *Step {
         elf_step.dependOn(testTlsDso(b, opts));
         elf_step.dependOn(testTlsGd(b, opts));
         elf_step.dependOn(testTlsIe(b, opts));
+        elf_step.dependOn(testTlsLd(b, opts));
         elf_step.dependOn(testTlsStatic(b, opts));
     }
 
@@ -860,6 +861,59 @@ fn testTlsIe(b: *Build, opts: Options) *Step {
     return test_step;
 }
 
+fn testTlsLd(b: *Build, opts: Options) *Step {
+    const test_step = b.step("test-elf-tls-ld", "");
+
+    const main_o = cc(b, null, opts);
+    main_o.addSourceBytes(
+        \\#include <stdio.h>
+        \\extern _Thread_local int foo;
+        \\static _Thread_local int bar;
+        \\int *get_foo_addr() { return &foo; }
+        \\int *get_bar_addr() { return &bar; }
+        \\int main() {
+        \\  bar = 5;
+        \\  printf("%d %d %d %d\n", *get_foo_addr(), *get_bar_addr(), foo, bar);
+        \\  return 0;
+        \\}
+    , "main.c");
+    main_o.addArgs(&.{ "-c", "-fPIC", "-ftls-model=local-dynamic" });
+    const main_o_out = main_o.saveOutputAs("main.o");
+
+    const a_o = cc(b, null, opts);
+    a_o.addSourceBytes(
+        \\_Thread_local int foo = 3;
+    , "a.c");
+    a_o.addArgs(&.{ "-c", "-fPIC", "-ftls-model=local-dynamic" });
+    const a_o_out = a_o.saveOutputAs("a.o");
+
+    const exp_stdout = "3 5 3 5\n";
+
+    {
+        const exe = cc(b, null, opts);
+        exe.addFileSource(main_o_out.file);
+        exe.addFileSource(a_o_out.file);
+        exe.addArg("-Wl,-relax");
+
+        const run = exe.run();
+        run.expectStdOutEqual(exp_stdout);
+        test_step.dependOn(run.step());
+    }
+
+    {
+        const exe = cc(b, null, opts);
+        exe.addFileSource(main_o_out.file);
+        exe.addFileSource(a_o_out.file);
+        exe.addArg("-Wl,-no-relax");
+
+        const run = exe.run();
+        run.expectStdOutEqual(exp_stdout);
+        test_step.dependOn(run.step());
+    }
+
+    return test_step;
+}
+
 fn testTlsStatic(b: *Build, opts: Options) *Step {
     const test_step = b.step("test-elf-tls-static", "");