elf: emit GOTTP placeholders in GOT

kubkon · Jul 12, 2023 · 12544e5 · 12544e5
1 parent 1c05728
commit 12544e5
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Showing 4 changed files with 72 additions and 7 deletions.
diff --git a/src/Elf.zig b/src/Elf.zig
@@ -1924,6 +1924,10 @@ fn scanRelocs(self: *Elf) !void {
             log.debug("'{s}' needs TLSGD", .{symbol.getName(self)});
             try self.got.addTlsGdSymbol(index, self);
         }
+        if (symbol.flags.gottp) {
+            log.debug("'{s}' needs GOTTP", .{symbol.getName(self)});
+            try self.got.addGotTpSymbol(index, self);
+        }
     }
 
     if (self.needs_tlsld) {

diff --git a/src/Elf/Atom.zig b/src/Elf/Atom.zig
@@ -244,7 +244,7 @@ pub fn scanRelocs(self: Atom, elf_file: *Elf) !void {
                     break :blk true;
                 };
                 if (!should_relax) {
-                    @panic("TODO");
+                    symbol.flags.gottp = true;
                 }
             },
 
@@ -585,9 +585,13 @@ pub fn resolveRelocsAlloc(self: Atom, elf_file: *Elf, writer: anytype) !void {
             elf.R_X86_64_DTPOFF64 => try cwriter.writeIntLittle(i64, S + A - DTP),
 
             elf.R_X86_64_GOTTPOFF => {
-                relaxGotTpOff(code[rel.r_offset - 3 ..]) catch
-                    elf_file.base.fatal("TODO could not rewrite GOTTPOFF", .{});
-                try cwriter.writeIntLittle(i32, @as(i32, @intCast(S - TP)));
+                if (target.flags.gottp) {
+                    const S_ = @as(i64, @intCast(target.getGotTpAddress(elf_file)));
+                    try cwriter.writeIntLittle(i32, @as(i32, @intCast(S_ + A - P)));
+                } else {
+                    try relaxGotTpOff(code[rel.r_offset - 3 ..]);
+                    try cwriter.writeIntLittle(i32, @as(i32, @intCast(S - TP)));
+                }
             },
 
             elf.R_X86_64_TLSGD => {

diff --git a/src/Elf/Symbol.zig b/src/Elf/Symbol.zig
@@ -105,12 +105,18 @@ pub fn getGotAddress(symbol: Symbol, elf_file: *Elf) u64 {
     return elf_file.getGotEntryAddress(extra.got);
 }
 
-pub inline fn getTlsGdAddress(symbol: Symbol, elf_file: *Elf) u64 {
+pub fn getTlsGdAddress(symbol: Symbol, elf_file: *Elf) u64 {
     if (!symbol.flags.tlsgd) return 0;
     const extra = symbol.getExtra(elf_file).?;
     return elf_file.getGotEntryAddress(extra.tlsgd);
 }
 
+pub fn getGotTpAddress(symbol: Symbol, elf_file: *Elf) u64 {
+    if (!symbol.flags.gottp) return 0;
+    const extra = symbol.getExtra(elf_file).?;
+    return elf_file.getGotEntryAddress(extra.gottp);
+}
+
 pub fn getAlignment(symbol: Symbol, elf_file: *Elf) !u64 {
     const file = symbol.getFile(elf_file) orelse return 0;
     const shared = file.shared;
@@ -286,6 +292,9 @@ pub const Flags = packed struct {
 
     /// Whether the symbol contains TLSGD indirection.
     tlsgd: bool = false,
+
+    /// Whether the symbol contains GOTTP indirection.
+    gottp: bool = false,
 };
 
 pub const Extra = struct {
@@ -295,6 +304,7 @@ pub const Extra = struct {
     dynamic: u32 = 0,
     copy_rel: u32 = 0,
     tlsgd: u32 = 0,
+    gottp: u32 = 0,
 };
 
 const std = @import("std");

diff --git a/src/Elf/synthetic.zig b/src/Elf/synthetic.zig
@@ -581,6 +581,7 @@ pub const GotSection = struct {
     const GotSymbol = union(enum) {
         got: u32,
         tlsgd: u32,
+        gottp: u32,
 
         pub inline fn getIndex(gt: GotSymbol) u32 {
             return switch (gt) {
@@ -617,10 +618,22 @@ pub const GotSection = struct {
         got.next_index += 2;
     }
 
+    pub fn addGotTpSymbol(got: *GotSection, sym_index: u32, elf_file: *Elf) !void {
+        const index = got.next_index;
+        const symbol = elf_file.getSymbol(sym_index);
+        if (symbol.getExtra(elf_file)) |extra| {
+            var new_extra = extra;
+            new_extra.gottp = index;
+            symbol.setExtra(new_extra, elf_file);
+        } else try symbol.addExtra(.{ .gottp = index }, elf_file);
+        try got.symbols.append(elf_file.base.allocator, .{ .gottp = sym_index });
+        got.next_index += 1;
+    }
+
     pub fn size(got: GotSection) usize {
         var s: usize = 0;
         for (got.symbols.items) |sym| switch (sym) {
-            .got => s += 8,
+            .got, .gottp => s += 8,
             .tlsgd => s += 16,
         };
         if (got.emit_tlsld) s += 8;
@@ -646,6 +659,15 @@ pub const GotSection = struct {
                         try writer.writeIntLittle(u64, symbol.getAddress(.{}, elf_file) - elf_file.getDtpAddress());
                     }
                 },
+                .gottp => {
+                    if (symbol.flags.import) {
+                        try writer.writeIntLittle(u64, 0);
+                    } else if (is_shared) {
+                        try writer.writeIntLittle(u64, symbol.getAddress(.{}, elf_file) - elf_file.getTlsAddress());
+                    } else {
+                        try writer.writeIntLittle(u64, symbol.getAddress(.{}, elf_file) - elf_file.getTpAddress());
+                    }
+                },
             }
         }
 
@@ -692,6 +714,7 @@ pub const GotSection = struct {
                         });
                     }
                 },
+
                 .tlsgd => {
                     const offset = symbol.getTlsGdAddress(elf_file);
 
@@ -714,6 +737,24 @@ pub const GotSection = struct {
                         });
                     }
                 },
+
+                .gottp => {
+                    const offset = symbol.getGotTpAddress(elf_file);
+
+                    if (symbol.flags.import) {
+                        elf_file.addRelaDynAssumeCapacity(.{
+                            .offset = offset,
+                            .sym = extra.dynamic,
+                            .type = elf.R_X86_64_TPOFF64,
+                        });
+                    } else if (is_shared) {
+                        elf_file.addRelaDynAssumeCapacity(.{
+                            .offset = offset,
+                            .type = elf.R_X86_64_TPOFF64,
+                            .addend = @intCast(symbol.getGotTpAddress(elf_file) - elf_file.getTlsAddress()),
+                        });
+                    }
+                },
             }
         }
     }
@@ -729,11 +770,14 @@ pub const GotSection = struct {
                 {
                     num += 1;
                 },
+
                 .tlsgd => if (symbol.flags.import) {
                     num += 2;
                 } else if (is_shared) {
                     num += 1;
                 },
+
+                .gottp => num += 1,
             }
         }
         return num;
@@ -747,6 +791,7 @@ pub const GotSection = struct {
             const suffix_len = switch (sym) {
                 .tlsgd => "$tlsgd".len,
                 .got => "$got".len,
+                .gottp => "$gottp".len,
             };
             const symbol = elf_file.getSymbol(sym.getIndex());
             const name_len = symbol.getName(elf_file).len;
@@ -769,6 +814,7 @@ pub const GotSection = struct {
             const suffix = switch (sym) {
                 .tlsgd => "$tlsgd",
                 .got => "$got",
+                .gottp => "$gottp",
             };
             const symbol = elf_file.getSymbol(sym.getIndex());
             const name = try std.fmt.allocPrint(gpa, "{s}{s}", .{ symbol.getName(elf_file), suffix });
@@ -777,10 +823,11 @@ pub const GotSection = struct {
             const st_value = switch (sym) {
                 .tlsgd => symbol.getTlsGdAddress(elf_file),
                 .got => symbol.getGotAddress(elf_file),
+                .gottp => symbol.getGotTpAddress(elf_file),
             };
             const st_size: u64 = switch (sym) {
                 .tlsgd => 16,
-                .got => 8,
+                .got, .gottp => 8,
             };
             ctx.symtab[ilocal] = .{
                 .st_name = st_name,