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macho: refactor calculating LEB128 sizes
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@kubkon
kubkon committed Dec 17, 2020
1 parent 3e9e793 commit b42ef0e
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Showing 3 changed files with 60 additions and 30 deletions.
16 changes: 2 additions & 14 deletions src/link/MachO.zig
View file
Original file line number Diff line number Diff line change
Expand Up @@ -826,7 +826,7 @@ fn linkWithLLD(self: *MachO, comp: *Compilation) !void {
// Write update dyld info
const dyld_info = self.load_commands.items[self.dyld_info_cmd_index.?].DyldInfoOnly;
{
const size = self.binding_info_table.calcSize();
const size = try self.binding_info_table.calcSize();
assert(dyld_info.bind_size >= size);

var buffer = try self.base.allocator.alloc(u8, size);
Expand All @@ -838,7 +838,7 @@ fn linkWithLLD(self: *MachO, comp: *Compilation) !void {
try self.base.file.?.pwriteAll(buffer, dyld_info.bind_off);
}
{
const size = self.lazy_binding_info_table.calcSize();
const size = try self.lazy_binding_info_table.calcSize();
assert(dyld_info.lazy_bind_size >= size);

var buffer = try self.base.allocator.alloc(u8, size);
Expand Down Expand Up @@ -2204,15 +2204,3 @@ fn parseLazyBindingInfoTable(self: *MachO) !void {
var stream = std.io.fixedBufferStream(buffer);
try self.lazy_binding_info_table.read(stream.reader(), self.base.allocator);
}

/// Calculates number of bytes in LEB128 encoding of value.
pub fn sizeLEB128(value: anytype) usize {
var res: usize = 0;
var v = value;
while (true) {
v = v >> 7;
res += 1;
if (v == 0) break;
}
return res;
}
20 changes: 12 additions & 8 deletions src/link/MachO/Trie.zig
View file
Original file line number Diff line number Diff line change
Expand Up @@ -38,7 +38,6 @@ const macho = std.macho;
const testing = std.testing;
const assert = std.debug.assert;
const Allocator = mem.Allocator;
const sizeLEB128 = @import("../MachO.zig").sizeLEB128;

pub const Node = struct {
base: *Trie,
Expand Down Expand Up @@ -242,28 +241,33 @@ pub const Node = struct {
};

/// Updates offset of this node in the output byte stream.
fn finalize(self: *Node, offset_in_trie: usize) FinalizeResult {
fn finalize(self: *Node, offset_in_trie: usize) !FinalizeResult {
var stream = std.io.countingWriter(std.io.null_writer);
var writer = stream.writer();

var node_size: usize = 0;
if (self.terminal_info) |info| {
node_size += sizeLEB128(info.export_flags);
node_size += sizeLEB128(info.vmaddr_offset);
node_size += sizeLEB128(node_size);
try leb.writeULEB128(writer, info.export_flags);
try leb.writeULEB128(writer, info.vmaddr_offset);
try leb.writeULEB128(writer, stream.bytes_written);
} else {
node_size += 1; // 0x0 for non-terminal nodes
}
node_size += 1; // 1 byte for edge count

for (self.edges.items) |edge| {
const next_node_offset = edge.to.trie_offset orelse 0;
node_size += edge.label.len + 1 + sizeLEB128(next_node_offset);
node_size += edge.label.len + 1;
try leb.writeULEB128(writer, next_node_offset);
}

const trie_offset = self.trie_offset orelse 0;
const updated = offset_in_trie != trie_offset;
self.trie_offset = offset_in_trie;
self.node_dirty = false;
node_size += stream.bytes_written;

return .{ .node_size = node_size, .updated = updated };
return FinalizeResult{ .node_size = node_size, .updated = updated };
}
};

Expand Down Expand Up @@ -347,7 +351,7 @@ pub fn finalize(self: *Trie) !void {
self.size = 0;
more = false;
for (self.ordered_nodes.items) |node| {
const res = node.finalize(self.size);
const res = try node.finalize(self.size);
self.size += res.node_size;
if (res.updated) more = true;
}
Expand Down
54 changes: 46 additions & 8 deletions src/link/MachO/imports.zig
View file
Original file line number Diff line number Diff line change
Expand Up @@ -5,7 +5,6 @@ const mem = std.mem;

const assert = std.debug.assert;
const Allocator = mem.Allocator;
const sizeLEB128 = @import("../MachO.zig").sizeLEB128;

/// Table of binding info entries used to tell the dyld which
/// symbols to bind at loading time.
Expand All @@ -27,6 +26,9 @@ pub const BindingInfoTable = struct {

/// Offset of this symbol wrt to the segment id encoded in `segment`.
offset: i64,

/// Addend value (if any).
addend: ?i64 = null,
};

pub fn deinit(self: *BindingInfoTable, allocator: *Allocator) void {
Expand Down Expand Up @@ -91,6 +93,9 @@ pub const BindingInfoTable = struct {
macho.BIND_OPCODE_SET_TYPE_IMM => {
self.binding_type = imm;
},
macho.BIND_OPCODE_SET_ADDEND_SLEB => {
symbol.addend = try leb.readILEB128(i64, reader);
},
else => {
std.log.warn("unhandled BIND_OPCODE_: 0x{x}", .{opcode});
},
Expand Down Expand Up @@ -121,17 +126,25 @@ pub const BindingInfoTable = struct {
try writer.writeByte(macho.BIND_OPCODE_SET_SEGMENT_AND_OFFSET_ULEB | @truncate(u4, symbol.segment));
try leb.writeILEB128(writer, symbol.offset);

if (symbol.addend) |addend| {
try writer.writeByte(macho.BIND_OPCODE_SET_ADDEND_SLEB);
try leb.writeILEB128(writer, addend);
}

try writer.writeByte(macho.BIND_OPCODE_DO_BIND);
}

try writer.writeByte(macho.BIND_OPCODE_DONE);
}

/// Calculate size in bytes of this binding info table.
pub fn calcSize(self: *BindingInfoTable) usize {
pub fn calcSize(self: *BindingInfoTable) !usize {
var stream = std.io.countingWriter(std.io.null_writer);
var writer = stream.writer();
var size: usize = 1;

if (self.dylib_ordinal > 15) {
size += sizeLEB128(self.dylib_ordinal);
try leb.writeULEB128(writer, @bitCast(u64, self.dylib_ordinal));
}

size += 1;
Expand All @@ -144,12 +157,17 @@ pub const BindingInfoTable = struct {
}

size += 1;
size += sizeLEB128(symbol.offset);
try leb.writeILEB128(writer, symbol.offset);

if (symbol.addend) |addend| {
size += 1;
try leb.writeILEB128(writer, addend);
}

size += 1;
}

size += 1;
size += 1 + stream.bytes_written;
return size;
}
};
Expand All @@ -173,6 +191,9 @@ pub const LazyBindingInfoTable = struct {

/// Id of the segment where to bind this symbol to.
segment: u8,

/// Addend value (if any).
addend: ?i64 = null,
};

pub fn deinit(self: *LazyBindingInfoTable, allocator: *Allocator) void {
Expand Down Expand Up @@ -232,6 +253,9 @@ pub const LazyBindingInfoTable = struct {
macho.BIND_OPCODE_SET_DYLIB_ORDINAL_ULEB => {
symbol.dylib_ordinal = try leb.readILEB128(i64, reader);
},
macho.BIND_OPCODE_SET_ADDEND_SLEB => {
symbol.addend = try leb.readILEB128(i64, reader);
},
else => {
std.log.warn("unhandled BIND_OPCODE_: 0x{x}", .{opcode});
},
Expand All @@ -246,6 +270,11 @@ pub const LazyBindingInfoTable = struct {
try writer.writeByte(macho.BIND_OPCODE_SET_SEGMENT_AND_OFFSET_ULEB | @truncate(u4, symbol.segment));
try leb.writeILEB128(writer, symbol.offset);

if (symbol.addend) |addend| {
try writer.writeByte(macho.BIND_OPCODE_SET_ADDEND_SLEB);
try leb.writeILEB128(writer, addend);
}

if (symbol.dylib_ordinal > 15) {
try writer.writeByte(macho.BIND_OPCODE_SET_DYLIB_ORDINAL_ULEB);
try leb.writeULEB128(writer, @bitCast(u64, symbol.dylib_ordinal));
Expand All @@ -267,15 +296,23 @@ pub const LazyBindingInfoTable = struct {
}

/// Calculate size in bytes of this binding info table.
pub fn calcSize(self: *LazyBindingInfoTable) usize {
pub fn calcSize(self: *LazyBindingInfoTable) !usize {
var stream = std.io.countingWriter(std.io.null_writer);
var writer = stream.writer();
var size: usize = 0;

for (self.symbols.items) |symbol| {
size += 1;
size += sizeLEB128(symbol.offset);
try leb.writeILEB128(writer, symbol.offset);

if (symbol.addend) |addend| {
size += 1;
try leb.writeILEB128(writer, addend);
}

size += 1;
if (symbol.dylib_ordinal > 15) {
size += sizeLEB128(symbol.dylib_ordinal);
try leb.writeULEB128(writer, @bitCast(u64, symbol.dylib_ordinal));
}
if (symbol.name) |name| {
size += 1;
Expand All @@ -285,6 +322,7 @@ pub const LazyBindingInfoTable = struct {
size += 2;
}

size += stream.bytes_written;
return size;
}
};

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