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elf: emit TLSGD placeholders in GOT
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@kubkon
kubkon committed Jul 12, 2023
1 parent a5fd559 commit 1c05728
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Showing 4 changed files with 172 additions and 57 deletions.
20 changes: 13 additions & 7 deletions src/Elf.zig
View file
Original file line number Diff line number Diff line change
Expand Up @@ -1900,7 +1900,7 @@ fn scanRelocs(self: *Elf) !void {
}
if (symbol.flags.got) {
log.debug("'{s}' needs GOT", .{symbol.getName(self)});
try self.got.addSymbol(index, self);
try self.got.addGotSymbol(index, self);
if (symbol.flags.import or symbol.isIFunc(self)) self.got.needs_rela = true;
}
if (symbol.flags.plt) {
Expand All @@ -1921,7 +1921,8 @@ fn scanRelocs(self: *Elf) !void {
try self.copy_rel.addSymbol(index, self);
}
if (symbol.flags.tlsgd) {
log.warn("'{s}' needs TLSGD", .{symbol.getName(self)});
log.debug("'{s}' needs TLSGD", .{symbol.getName(self)});
try self.got.addTlsGdSymbol(index, self);
}
}

Expand Down Expand Up @@ -2447,9 +2448,10 @@ fn sortRelaDyn(self: *Elf) void {
fn getNumIRelativeRelocs(self: *Elf) usize {
var count: usize = self.num_ifunc_dynrelocs;

for (self.got.symbols.items) |sym_index| {
const sym = self.getSymbol(sym_index);
if (sym.isIFunc(self)) count += 1;
for (self.got.symbols.items) |sym| {
if (sym != .got) continue;
const symbol = self.getSymbol(sym.getIndex());
if (symbol.isIFunc(self)) count += 1;
}

return count;
Expand Down Expand Up @@ -2600,8 +2602,12 @@ fn fmtDumpState(
try writer.print("{}\n", .{internal.fmtSymtab(self)});
}
try writer.writeAll("GOT\n");
for (self.got.symbols.items, 0..) |sym_index, i| {
try writer.print(" {d} => {d} '{s}'\n", .{ i, sym_index, self.getSymbol(sym_index).getName(self) });
for (self.got.symbols.items) |sym| {
try writer.print(" ({s}) {d} '{s}'\n", .{
@tagName(sym),
sym.getIndex(),
self.getSymbol(sym.getIndex()).getName(self),
});
}
try writer.writeByte('\n');
try writer.writeAll("PLT\n");
Expand Down
3 changes: 2 additions & 1 deletion src/Elf/Atom.zig
View file
Original file line number Diff line number Diff line change
Expand Up @@ -592,7 +592,8 @@ pub fn resolveRelocsAlloc(self: Atom, elf_file: *Elf, writer: anytype) !void {

elf.R_X86_64_TLSGD => {
if (target.flags.tlsgd) {
elf_file.base.fatal("TODO get TLSGD address of the symbol '{s}'", .{target.getName(elf_file)});
const S_ = @as(i64, @intCast(target.getTlsGdAddress(elf_file)));
try cwriter.writeIntLittle(i32, @as(i32, @intCast(S_ + A - P)));
} else {
try relaxTlsGdToLe(
relocs[i .. i + 2],
Expand Down
7 changes: 7 additions & 0 deletions src/Elf/Symbol.zig
View file
Original file line number Diff line number Diff line change
Expand Up @@ -105,6 +105,12 @@ 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 {
if (!symbol.flags.tlsgd) return 0;
const extra = symbol.getExtra(elf_file).?;
return elf_file.getGotEntryAddress(extra.tlsgd);
}

pub fn getAlignment(symbol: Symbol, elf_file: *Elf) !u64 {
const file = symbol.getFile(elf_file) orelse return 0;
const shared = file.shared;
Expand Down Expand Up @@ -288,6 +294,7 @@ pub const Extra = struct {
plt_got: u32 = 0,
dynamic: u32 = 0,
copy_rel: u32 = 0,
tlsgd: u32 = 0,
};

const std = @import("std");
Expand Down
199 changes: 150 additions & 49 deletions src/Elf/synthetic.zig
View file
Original file line number Diff line number Diff line change
Expand Up @@ -572,37 +572,81 @@ pub const VerneedSection = struct {
};

pub const GotSection = struct {
symbols: std.ArrayListUnmanaged(u32) = .{},
symbols: std.ArrayListUnmanaged(GotSymbol) = .{},
needs_rela: bool = false,
emit_tlsld: bool = false,
output_symtab_size: Elf.SymtabSize = .{},
next_index: u32 = 0,

const GotSymbol = union(enum) {
got: u32,
tlsgd: u32,

pub inline fn getIndex(gt: GotSymbol) u32 {
return switch (gt) {
inline else => |x| x,
};
}
};

pub fn deinit(got: *GotSection, allocator: Allocator) void {
got.symbols.deinit(allocator);
}

pub fn addSymbol(got: *GotSection, sym_index: u32, elf_file: *Elf) !void {
const index = @as(u32, @intCast(got.symbols.items.len));
pub fn addGotSymbol(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.got = index;
symbol.setExtra(new_extra, elf_file);
} else try symbol.addExtra(.{ .got = index }, elf_file);
try got.symbols.append(elf_file.base.allocator, sym_index);
try got.symbols.append(elf_file.base.allocator, .{ .got = sym_index });
got.next_index += 1;
}

pub fn addTlsGdSymbol(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.tlsgd = index;
symbol.setExtra(new_extra, elf_file);
} else try symbol.addExtra(.{ .tlsgd = index }, elf_file);
try got.symbols.append(elf_file.base.allocator, .{ .tlsgd = sym_index });
got.next_index += 2;
}

pub fn size(got: GotSection) usize {
var s = got.symbols.items.len * 8;
var s: usize = 0;
for (got.symbols.items) |sym| switch (sym) {
.got => s += 8,
.tlsgd => s += 16,
};
if (got.emit_tlsld) s += 8;
return s;
}

pub fn write(got: GotSection, elf_file: *Elf, writer: anytype) !void {
for (got.symbols.items) |sym_index| {
const sym = elf_file.getSymbol(sym_index);
const value = if (sym.flags.import) 0 else sym.value;
try writer.writeIntLittle(u64, value);
const is_shared = elf_file.options.output_mode == .lib;

for (got.symbols.items) |sym| {
const symbol = elf_file.getSymbol(sym.getIndex());
switch (sym) {
.got => {
const value = if (symbol.flags.import) 0 else symbol.value;
try writer.writeIntLittle(u64, value);
},
.tlsgd => {
if (symbol.flags.import) {
try writer.writeIntLittle(u64, 0);
try writer.writeIntLittle(u64, 0);
} else {
try writer.writeIntLittle(u64, if (is_shared) @as(u64, 0) else 1);
try writer.writeIntLittle(u64, symbol.getAddress(.{}, elf_file) - elf_file.getDtpAddress());
}
},
}
}

if (got.emit_tlsld) {
Expand All @@ -611,46 +655,86 @@ pub const GotSection = struct {
}

pub fn addRela(got: GotSection, elf_file: *Elf) !void {
const is_shared = elf_file.options.output_mode == .lib;
try elf_file.rela_dyn.ensureUnusedCapacity(elf_file.base.allocator, got.numRela(elf_file));
for (got.symbols.items, 0..) |sym_index, i| {
const sym = elf_file.getSymbol(sym_index);
const offset = elf_file.getGotEntryAddress(@as(u32, @intCast(i)));
const extra = sym.getExtra(elf_file).?;

if (sym.flags.import) {
elf_file.addRelaDynAssumeCapacity(.{
.offset = offset,
.sym = extra.dynamic,
.type = elf.R_X86_64_GLOB_DAT,
});
continue;
}

if (sym.isIFunc(elf_file)) {
elf_file.addRelaDynAssumeCapacity(.{
.offset = offset,
.type = elf.R_X86_64_IRELATIVE,
.addend = @intCast(sym.getAddress(.{ .plt = false }, elf_file)),
});
continue;
}

if (elf_file.options.pic and !sym.isAbs(elf_file)) {
elf_file.addRelaDynAssumeCapacity(.{
.offset = offset,
.type = elf.R_X86_64_RELATIVE,
.addend = @intCast(sym.getAddress(.{ .plt = false }, elf_file)),
});
for (got.symbols.items) |sym| {
const symbol = elf_file.getSymbol(sym.getIndex());
const extra = symbol.getExtra(elf_file).?;

switch (sym) {
.got => {
const offset = symbol.getGotAddress(elf_file);

if (symbol.flags.import) {
elf_file.addRelaDynAssumeCapacity(.{
.offset = offset,
.sym = extra.dynamic,
.type = elf.R_X86_64_GLOB_DAT,
});
continue;
}

if (symbol.isIFunc(elf_file)) {
elf_file.addRelaDynAssumeCapacity(.{
.offset = offset,
.type = elf.R_X86_64_IRELATIVE,
.addend = @intCast(symbol.getAddress(.{ .plt = false }, elf_file)),
});
continue;
}

if (elf_file.options.pic and !symbol.isAbs(elf_file)) {
elf_file.addRelaDynAssumeCapacity(.{
.offset = offset,
.type = elf.R_X86_64_RELATIVE,
.addend = @intCast(symbol.getAddress(.{ .plt = false }, elf_file)),
});
}
},
.tlsgd => {
const offset = symbol.getTlsGdAddress(elf_file);

if (symbol.flags.import) {
elf_file.addRelaDynAssumeCapacity(.{
.offset = offset,
.sym = extra.dynamic,
.type = elf.R_X86_64_DTPMOD64,
});
elf_file.addRelaDynAssumeCapacity(.{
.offset = offset + 8,
.sym = extra.dynamic,
.type = elf.R_X86_64_DTPOFF64,
});
} else if (is_shared) {
elf_file.addRelaDynAssumeCapacity(.{
.offset = offset,
.sym = extra.dynamic,
.type = elf.R_X86_64_DTPMOD64,
});
}
},
}
}
}

pub fn numRela(got: GotSection, elf_file: *Elf) usize {
const is_shared = elf_file.options.output_mode == .lib;
var num: usize = 0;
for (got.symbols.items) |sym_index| {
const sym = elf_file.getSymbol(sym_index);
if (sym.flags.import or sym.isIFunc(elf_file) or (elf_file.options.pic and !sym.isAbs(elf_file)))
num += 1;
for (got.symbols.items) |sym| {
const symbol = elf_file.getSymbol(sym.getIndex());
switch (sym) {
.got => if (symbol.flags.import or
symbol.isIFunc(elf_file) or (elf_file.options.pic and !symbol.isAbs(elf_file)))
{
num += 1;
},
.tlsgd => if (symbol.flags.import) {
num += 2;
} else if (is_shared) {
num += 1;
},
}
}
return num;
}
Expand All @@ -659,9 +743,14 @@ pub const GotSection = struct {
if (elf_file.options.strip_all) return;

got.output_symtab_size.nlocals = @as(u32, @intCast(got.symbols.items.len));
for (got.symbols.items) |sym_index| {
const sym = elf_file.getSymbol(sym_index);
got.output_symtab_size.strsize += @as(u32, @intCast(sym.getName(elf_file).len + "$got".len + 1));
for (got.symbols.items) |sym| {
const suffix_len = switch (sym) {
.tlsgd => "$tlsgd".len,
.got => "$got".len,
};
const symbol = elf_file.getSymbol(sym.getIndex());
const name_len = symbol.getName(elf_file).len;
got.output_symtab_size.strsize += @as(u32, @intCast(name_len + suffix_len + 1));
}

if (got.emit_tlsld) {
Expand All @@ -676,18 +765,30 @@ pub const GotSection = struct {
const gpa = elf_file.base.allocator;

var ilocal = ctx.ilocal;
for (got.symbols.items) |sym_index| {
const sym = elf_file.getSymbol(sym_index);
const name = try std.fmt.allocPrint(gpa, "{s}$got", .{sym.getName(elf_file)});
for (got.symbols.items) |sym| {
const suffix = switch (sym) {
.tlsgd => "$tlsgd",
.got => "$got",
};
const symbol = elf_file.getSymbol(sym.getIndex());
const name = try std.fmt.allocPrint(gpa, "{s}{s}", .{ symbol.getName(elf_file), suffix });
defer gpa.free(name);
const st_name = try ctx.strtab.insert(gpa, name);
const st_value = switch (sym) {
.tlsgd => symbol.getTlsGdAddress(elf_file),
.got => symbol.getGotAddress(elf_file),
};
const st_size: u64 = switch (sym) {
.tlsgd => 16,
.got => 8,
};
ctx.symtab[ilocal] = .{
.st_name = st_name,
.st_info = elf.STT_OBJECT,
.st_other = 0,
.st_shndx = elf_file.got_sect_index.?,
.st_value = elf_file.getGotEntryAddress(ilocal),
.st_size = @sizeOf(u64),
.st_value = st_value,
.st_size = st_size,
};
ilocal += 1;
}
Expand Down

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