motiejus/zig
1
Fork 0
Code Releases Activity

macho: ensure that strtab always follows symtab

Browse Source 
In rare occassions, it may happen that string table is allocated free
space preceeding symbol table. This is an error in the eyes of the `dyld`
dynamic loader and thus has to forbidden by the linker.
This commit is contained in:
Jakub Konka
2021-01-15 17:33:36 +01:00
parent f7d7cb6268
commit b204ea0349
3 changed files with 60 additions and 19 deletions
Download Patch File Download Diff File Expand all files Collapse all files

47
src/link/MachO.zig
View File

@@ -135,6 +135,8 @@ lazy_binding_info_dirty: bool = false,
export_info_dirty: bool = false,
string_table_dirty: bool = false,
string_table_needs_relocation: bool = false,
/// A list of text blocks that have surplus capacity. This list can have false
/// positives, as functions grow and shrink over time, only sometimes being added
/// or removed from the freelist.
@@ -454,6 +456,7 @@ pub fn flushModule(self: *MachO, comp: *Compilation) !void {
assert(!self.lazy_binding_info_dirty);
assert(!self.export_info_dirty);
assert(!self.string_table_dirty);
assert(!self.string_table_needs_relocation);
if (target.cpu.arch == .aarch64) {
switch (output_mode) {
@@ -1824,22 +1827,22 @@ pub fn populateMissingMetadata(self: *MachO) !void {
// Preallocate rebase, binding, lazy binding info, and export info.
const expected_size = 48; // TODO This is totally random.
const rebase_off = self.findFreeSpaceLinkedit(expected_size, 1);
const rebase_off = self.findFreeSpaceLinkedit(expected_size, 1, null);
log.debug("found rebase info free space 0x{x} to 0x{x}", .{ rebase_off, rebase_off + expected_size });
dyld.rebase_off = @intCast(u32, rebase_off);
dyld.rebase_size = expected_size;
const bind_off = self.findFreeSpaceLinkedit(expected_size, 1);
const bind_off = self.findFreeSpaceLinkedit(expected_size, 1, null);
log.debug("found binding info free space 0x{x} to 0x{x}", .{ bind_off, bind_off + expected_size });
dyld.bind_off = @intCast(u32, bind_off);
dyld.bind_size = expected_size;
const lazy_bind_off = self.findFreeSpaceLinkedit(expected_size, 1);
const lazy_bind_off = self.findFreeSpaceLinkedit(expected_size, 1, null);
log.debug("found lazy binding info free space 0x{x} to 0x{x}", .{ lazy_bind_off, lazy_bind_off + expected_size });
dyld.lazy_bind_off = @intCast(u32, lazy_bind_off);
dyld.lazy_bind_size = expected_size;
const export_off = self.findFreeSpaceLinkedit(expected_size, 1);
const export_off = self.findFreeSpaceLinkedit(expected_size, 1, null);
log.debug("found export info free space 0x{x} to 0x{x}", .{ export_off, export_off + expected_size });
dyld.export_off = @intCast(u32, export_off);
dyld.export_size = expected_size;
@@ -1864,14 +1867,14 @@ pub fn populateMissingMetadata(self: *MachO) !void {
const symtab = &self.load_commands.items[self.symtab_cmd_index.?].Symtab;
const symtab_size = self.base.options.symbol_count_hint * @sizeOf(macho.nlist_64);
const symtab_off = self.findFreeSpaceLinkedit(symtab_size, @sizeOf(macho.nlist_64));
const symtab_off = self.findFreeSpaceLinkedit(symtab_size, @sizeOf(macho.nlist_64), null);
log.debug("found symbol table free space 0x{x} to 0x{x}", .{ symtab_off, symtab_off + symtab_size });
symtab.symoff = @intCast(u32, symtab_off);
symtab.nsyms = @intCast(u32, self.base.options.symbol_count_hint);
try self.string_table.append(self.base.allocator, 0); // Need a null at position 0.
const strtab_size = self.string_table.items.len;
const strtab_off = self.findFreeSpaceLinkedit(strtab_size, 1);
const strtab_off = self.findFreeSpaceLinkedit(strtab_size, 1, symtab_off);
log.debug("found string table free space 0x{x} to 0x{x}", .{ strtab_off, strtab_off + strtab_size });
symtab.stroff = @intCast(u32, strtab_off);
symtab.strsize = @intCast(u32, strtab_size);
@@ -1885,7 +1888,7 @@ pub fn populateMissingMetadata(self: *MachO) !void {
// Preallocate space for indirect symbol table.
const indsymtab_size = self.base.options.symbol_count_hint * @sizeOf(u64); // Each entry is just a u64.
const indsymtab_off = self.findFreeSpaceLinkedit(indsymtab_size, @sizeOf(u64));
const indsymtab_off = self.findFreeSpaceLinkedit(indsymtab_size, @sizeOf(u64), null);
log.debug("found indirect symbol table free space 0x{x} to 0x{x}", .{ indsymtab_off, indsymtab_off + indsymtab_size });
@@ -2383,13 +2386,13 @@ fn detectAllocCollisionLinkedit(self: *MachO, start: u64, size: u64) ?u64 {
return null;
}
fn findFreeSpaceLinkedit(self: *MachO, object_size: u64, min_alignment: u16) u64 {
fn findFreeSpaceLinkedit(self: *MachO, object_size: u64, min_alignment: u16, start: ?u64) u64 {
const linkedit = self.load_commands.items[self.linkedit_segment_cmd_index.?].Segment;
var start: u64 = linkedit.inner.fileoff;
while (self.detectAllocCollisionLinkedit(start, object_size)) |item_end| {
start = mem.alignForwardGeneric(u64, item_end, min_alignment);
var st: u64 = start orelse linkedit.inner.fileoff;
while (self.detectAllocCollisionLinkedit(st, object_size)) |item_end| {
st = mem.alignForwardGeneric(u64, item_end, min_alignment);
}
return start;
return st;
}
/// Saturating multiplication
@@ -2535,7 +2538,7 @@ fn relocateSymbolTable(self: *MachO) !void {
const needed_size = nsyms * @sizeOf(macho.nlist_64);
if (needed_size > self.allocatedSizeLinkedit(symtab.symoff)) {
// Move the entire symbol table to a new location
const new_symoff = self.findFreeSpaceLinkedit(needed_size, @alignOf(macho.nlist_64));
const new_symoff = self.findFreeSpaceLinkedit(needed_size, @alignOf(macho.nlist_64), null);
const existing_size = symtab.nsyms * @sizeOf(macho.nlist_64);
log.debug("relocating symbol table from 0x{x}-0x{x} to 0x{x}-0x{x}", .{
@@ -2548,6 +2551,7 @@ fn relocateSymbolTable(self: *MachO) !void {
const amt = try self.base.file.?.copyRangeAll(symtab.symoff, self.base.file.?, new_symoff, existing_size);
if (amt != existing_size) return error.InputOutput;
symtab.symoff = @intCast(u32, new_symoff);
self.string_table_needs_relocation = true;
}
symtab.nsyms = @intCast(u32, nsyms);
self.load_commands_dirty = true;
@@ -2757,7 +2761,8 @@ fn writeExportTrie(self: *MachO) !void {
if (needed_size > allocated_size) {
dyld_info.export_off = 0;
dyld_info.export_off = @intCast(u32, self.findFreeSpaceLinkedit(needed_size, 1));
dyld_info.export_off = @intCast(u32, self.findFreeSpaceLinkedit(needed_size, 1, null));
// TODO this might require relocating all following LC_DYLD_INFO_ONLY sections too.
}
dyld_info.export_size = @intCast(u32, needed_size);
log.debug("writing export info from 0x{x} to 0x{x}", .{ dyld_info.export_off, dyld_info.export_off + dyld_info.export_size });
@@ -2794,7 +2799,8 @@ fn writeRebaseInfoTable(self: *MachO) !void {
if (needed_size > allocated_size) {
dyld_info.rebase_off = 0;
dyld_info.rebase_off = @intCast(u32, self.findFreeSpaceLinkedit(needed_size, 1));
dyld_info.rebase_off = @intCast(u32, self.findFreeSpaceLinkedit(needed_size, 1, null));
// TODO this might require relocating all following LC_DYLD_INFO_ONLY sections too.
}
dyld_info.rebase_size = @intCast(u32, needed_size);
@@ -2832,7 +2838,8 @@ fn writeBindingInfoTable(self: *MachO) !void {
if (needed_size > allocated_size) {
dyld_info.bind_off = 0;
dyld_info.bind_off = @intCast(u32, self.findFreeSpaceLinkedit(needed_size, 1));
dyld_info.bind_off = @intCast(u32, self.findFreeSpaceLinkedit(needed_size, 1, null));
// TODO this might require relocating all following LC_DYLD_INFO_ONLY sections too.
}
dyld_info.bind_size = @intCast(u32, needed_size);
@@ -2867,7 +2874,8 @@ fn writeLazyBindingInfoTable(self: *MachO) !void {
if (needed_size > allocated_size) {
dyld_info.lazy_bind_off = 0;
dyld_info.lazy_bind_off = @intCast(u32, self.findFreeSpaceLinkedit(needed_size, 1));
dyld_info.lazy_bind_off = @intCast(u32, self.findFreeSpaceLinkedit(needed_size, 1, null));
// TODO this might require relocating all following LC_DYLD_INFO_ONLY sections too.
}
dyld_info.lazy_bind_size = @intCast(u32, needed_size);
@@ -2956,9 +2964,10 @@ fn writeStringTable(self: *MachO) !void {
const allocated_size = self.allocatedSizeLinkedit(symtab.stroff);
const needed_size = mem.alignForwardGeneric(u64, self.string_table.items.len, @alignOf(u64));
if (needed_size > allocated_size) {
if (needed_size > allocated_size or self.string_table_needs_relocation) {
symtab.strsize = 0;
symtab.stroff = @intCast(u32, self.findFreeSpaceLinkedit(needed_size, 1));
symtab.stroff = @intCast(u32, self.findFreeSpaceLinkedit(needed_size, 1, symtab.symoff));
self.string_table_needs_relocation = false;
}
symtab.strsize = @intCast(u32, needed_size);
log.debug("writing string table from 0x{x} to 0x{x}", .{ symtab.stroff, symtab.stroff + symtab.strsize });

16
test/stage2/aarch64.zig
View File

@@ -217,4 +217,20 @@ pub fn addCases(ctx: *TestContext) !void {
"Hello, World!\n",
);
}
{
var case = ctx.exe("only libc exit", macos_aarch64);
// This test case covers an infrequent scenarion where the string table *may* be relocated
// into the position preceeding the symbol table which results in a dyld error.
case.addCompareOutput(
\\extern "c" fn exit(usize) noreturn;
\\
\\export fn _start() noreturn {
\\ exit(0);
\\}
,
"",
);
}
}

16
test/stage2/test.zig
View File

@@ -1513,4 +1513,20 @@ pub fn addCases(ctx: *TestContext) !void {
"Hello, World!\n",
);
}
{
var case = ctx.exe("only libc exit", macosx_x64);
// This test case covers an infrequent scenarion where the string table *may* be relocated
// into the position preceeding the symbol table which results in a dyld error.
case.addCompareOutput(
\\extern "c" fn exit(usize) noreturn;
\\
\\export fn _start() noreturn {
\\ exit(0);
\\}
,
"",
);
}
}