[lld/mac] Add support for -flat_namespace
-flat_namespace makes lld emit binaries that use name lookup that's more in
line with other POSIX systems: Instead of looking up symbols as (dylib,name)
pairs by dyld, they're instead looked up just by name.
-flat_namespace has three effects:
1. MH_TWOLEVEL and MH_NNOUNDEFS are no longer set in the Mach-O header
2. All symbols use BIND_SPECIAL_DYLIB_FLAT_LOOKUP as ordinal
3. When a dylib is added to the link, its dependent dylibs are also added,
so that lld can verify that no undefined symbols remain at the end of
a link with -flat_namespace. These transitive dylibs are added for symbol
resolution, but they are not emitted in LC_LOAD_COMMANDs.
-undefined with -flat_namespace still isn't implemented. Before this change,
it was impossible to hit that combination because -flat_namespace caused a
diagnostic. Now that it no longer does, emit a dedicated temporary diagnostic
when both flags are used.
Differential Revision: https://reviews.llvm.org/D97641
GitOrigin-RevId: 8174f33dc9bf34e1cde57931e2e028bd4d49c98e
diff --git a/MachO/Driver.cpp b/MachO/Driver.cpp
index e3a2b60..b27c2f1 100644
--- a/MachO/Driver.cpp
+++ b/MachO/Driver.cpp
@@ -796,11 +796,6 @@
config->namespaceKind = arg->getOption().getID() == OPT_twolevel_namespace
? NamespaceKind::twolevel
: NamespaceKind::flat;
- if (config->namespaceKind == NamespaceKind::flat) {
- warn("Option '" + arg->getOption().getPrefixedName() +
- "' is not yet implemented. Stay tuned...");
- config->namespaceKind = NamespaceKind::twolevel;
- }
}
config->systemLibraryRoots = getSystemLibraryRoots(args);
diff --git a/MachO/InputFiles.cpp b/MachO/InputFiles.cpp
index 726ce12..dd1b655 100644
--- a/MachO/InputFiles.cpp
+++ b/MachO/InputFiles.cpp
@@ -587,15 +587,14 @@
// Re-exports can either refer to on-disk files, or to documents within .tbd
// files.
-static Optional<DylibFile *> loadReexportHelper(StringRef path,
- DylibFile *umbrella) {
+static Optional<DylibFile *> findDylib(StringRef path, DylibFile *umbrella) {
if (path::is_absolute(path, path::Style::posix))
for (StringRef root : config->systemLibraryRoots)
if (Optional<std::string> dylibPath =
resolveDylibPath((root + path).str()))
return loadDylib(*dylibPath, umbrella);
- // TODO: Expand @loader_path, @executable_path etc
+ // TODO: Expand @loader_path, @executable_path, @rpath etc, handle -dylib_path
if (currentTopLevelTapi) {
for (InterfaceFile &child :
@@ -609,7 +608,6 @@
if (Optional<std::string> dylibPath = resolveDylibPath(path))
return loadDylib(*dylibPath, umbrella);
- error("unable to locate re-export with install name " + path);
return {};
}
@@ -634,8 +632,10 @@
}
void loadReexport(StringRef path, DylibFile *umbrella) {
- Optional<DylibFile *> reexport = loadReexportHelper(path, umbrella);
- if (reexport && isImplicitlyLinked(path))
+ Optional<DylibFile *> reexport = findDylib(path, umbrella);
+ if (!reexport)
+ error("unable to locate re-export with install name " + path);
+ else if (isImplicitlyLinked(path))
inputFiles.insert(*reexport);
}
@@ -679,21 +679,33 @@
return;
}
- if (hdr->flags & MH_NO_REEXPORTED_DYLIBS)
- return;
-
const uint8_t *p =
reinterpret_cast<const uint8_t *>(hdr) + sizeof(mach_header_64);
for (uint32_t i = 0, n = hdr->ncmds; i < n; ++i) {
auto *cmd = reinterpret_cast<const load_command *>(p);
p += cmd->cmdsize;
- if (cmd->cmd != LC_REEXPORT_DYLIB)
- continue;
- auto *c = reinterpret_cast<const dylib_command *>(cmd);
- StringRef reexportPath =
- reinterpret_cast<const char *>(c) + read32le(&c->dylib.name);
- loadReexport(reexportPath, umbrella);
+ if (!(hdr->flags & MH_NO_REEXPORTED_DYLIBS) &&
+ cmd->cmd == LC_REEXPORT_DYLIB) {
+ const auto *c = reinterpret_cast<const dylib_command *>(cmd);
+ StringRef reexportPath =
+ reinterpret_cast<const char *>(c) + read32le(&c->dylib.name);
+ loadReexport(reexportPath, umbrella);
+ }
+
+ // FIXME: What about LC_LOAD_UPWARD_DYLIB, LC_LAZY_LOAD_DYLIB,
+ // LC_LOAD_WEAK_DYLIB, LC_REEXPORT_DYLIB (..are reexports from dylibs with
+ // MH_NO_REEXPORTED_DYLIBS loaded for -flat_namespace)?
+ if (config->namespaceKind == NamespaceKind::flat &&
+ cmd->cmd == LC_LOAD_DYLIB) {
+ const auto *c = reinterpret_cast<const dylib_command *>(cmd);
+ StringRef dylibPath =
+ reinterpret_cast<const char *>(c) + read32le(&c->dylib.name);
+ Optional<DylibFile *> dylib = findDylib(dylibPath, umbrella);
+ if (!dylib)
+ error(Twine("unable to locate library '") + dylibPath +
+ "' loaded from '" + toString(this) + "' for -flat_namespace");
+ }
}
}
diff --git a/MachO/Options.td b/MachO/Options.td
index 84006ad..1349b64 100644
--- a/MachO/Options.td
+++ b/MachO/Options.td
@@ -448,7 +448,6 @@
Group<grp_resolve>;
def flat_namespace : Flag<["-"], "flat_namespace">,
HelpText<"Resolve symbols from all dylibs, both direct and transitive. Do not record source libraries: dyld must re-search at runtime and use the first definition found">,
- Flags<[HelpHidden]>,
Group<grp_resolve>;
def twolevel_namespace : Flag<["-"], "twolevel_namespace">,
HelpText<"Make dyld look up symbols by (dylib,name) pairs (default)">,
diff --git a/MachO/SymbolTable.cpp b/MachO/SymbolTable.cpp
index 96ed3ef..1d1e7a0 100644
--- a/MachO/SymbolTable.cpp
+++ b/MachO/SymbolTable.cpp
@@ -181,12 +181,14 @@
message += "\n>>> referenced by " + fileName;
switch (config->undefinedSymbolTreatment) {
case UndefinedSymbolTreatment::suppress:
+ error("-undefined suppress unimplemented");
break;
case UndefinedSymbolTreatment::error:
error(message);
break;
case UndefinedSymbolTreatment::warning:
warn(message);
+ error("-undefined warning unimplemented");
break;
case UndefinedSymbolTreatment::dynamic_lookup:
error("dynamic_lookup unimplemented for " + message);
diff --git a/MachO/SyntheticSections.cpp b/MachO/SyntheticSections.cpp
index 6e21986..27c0996 100644
--- a/MachO/SyntheticSections.cpp
+++ b/MachO/SyntheticSections.cpp
@@ -78,7 +78,10 @@
hdr->filetype = config->outputType;
hdr->ncmds = loadCommands.size();
hdr->sizeofcmds = sizeOfCmds;
- hdr->flags = MachO::MH_NOUNDEFS | MachO::MH_DYLDLINK | MachO::MH_TWOLEVEL;
+ hdr->flags = MachO::MH_DYLDLINK;
+
+ if (config->namespaceKind == NamespaceKind::twolevel)
+ hdr->flags |= MachO::MH_NOUNDEFS | MachO::MH_TWOLEVEL;
if (config->outputType == MachO::MH_DYLIB && !config->hasReexports)
hdr->flags |= MachO::MH_NO_REEXPORTED_DYLIBS;
@@ -280,8 +283,9 @@
// Non-weak bindings need to have their dylib ordinal encoded as well.
static int16_t ordinalForDylibSymbol(const DylibSymbol &dysym) {
- return dysym.isDynamicLookup() ? MachO::BIND_SPECIAL_DYLIB_FLAT_LOOKUP
- : dysym.getFile()->ordinal;
+ return config->namespaceKind == NamespaceKind::flat || dysym.isDynamicLookup()
+ ? MachO::BIND_SPECIAL_DYLIB_FLAT_LOOKUP
+ : dysym.getFile()->ordinal;
}
static void encodeDylibOrdinal(int16_t ordinal, raw_svector_ostream &os) {
@@ -816,13 +820,15 @@
nList->n_desc |= defined->isExternalWeakDef() ? MachO::N_WEAK_DEF : 0;
} else if (auto *dysym = dyn_cast<DylibSymbol>(entry.sym)) {
uint16_t n_desc = nList->n_desc;
- if (dysym->isDynamicLookup())
+ int16_t ordinal = ordinalForDylibSymbol(*dysym);
+ if (ordinal == MachO::BIND_SPECIAL_DYLIB_FLAT_LOOKUP)
MachO::SET_LIBRARY_ORDINAL(n_desc, MachO::DYNAMIC_LOOKUP_ORDINAL);
- else if (dysym->getFile()->isBundleLoader)
+ else if (ordinal == MachO::BIND_SPECIAL_DYLIB_MAIN_EXECUTABLE)
MachO::SET_LIBRARY_ORDINAL(n_desc, MachO::EXECUTABLE_ORDINAL);
- else
- MachO::SET_LIBRARY_ORDINAL(
- n_desc, static_cast<uint8_t>(dysym->getFile()->ordinal));
+ else {
+ assert(ordinal > 0);
+ MachO::SET_LIBRARY_ORDINAL(n_desc, static_cast<uint8_t>(ordinal));
+ }
nList->n_type = MachO::N_EXT;
n_desc |= dysym->isWeakDef() ? MachO::N_WEAK_DEF : 0;
diff --git a/test/MachO/flat-namespace.s b/test/MachO/flat-namespace.s
new file mode 100644
index 0000000..125b846
--- /dev/null
+++ b/test/MachO/flat-namespace.s
@@ -0,0 +1,87 @@
+# REQUIRES: x86
+# RUN: rm -rf %t
+# RUN: split-file %s %t
+
+# RUN: llvm-mc -filetype=obj -triple=x86_64-apple-macos -o %t/foo.o %t/foo.s
+# RUN: %lld -dylib -o %t/foo.dylib %t/foo.o
+
+# RUN: llvm-mc -filetype=obj -triple=x86_64-apple-macos -o %t/bar.o %t/bar.s
+# RUN: %lld -lSystem -dylib -o %t/bar.dylib %t/bar.o %t/foo.dylib
+
+# RUN: llvm-mc -filetype=obj -triple=x86_64-apple-macos -o %t/baz.o %t/baz.s
+# RUN: %lld -lSystem -dylib -o %t/baz.dylib %t/baz.o %t/bar.dylib
+
+# RUN: llvm-mc -filetype=obj -triple=x86_64-apple-macos -o %t/main.o %t/main.s
+
+# With flat_namespace, the linker automatically looks in foo.dylib and
+# bar.dylib too, but it doesn't add a LC_LOAD_DYLIB for it.
+# RUN: %lld -flat_namespace -lSystem %t/main.o %t/baz.dylib -o %t/out
+# RUN: llvm-objdump --macho --all-headers %t/out \
+# RUN: | FileCheck --check-prefix=HEADERBITS %s
+# RUN: llvm-objdump --macho --bind --lazy-bind --weak-bind %t/out \
+# RUN: | FileCheck --check-prefix=FLAT %s
+# RUN: llvm-nm -m %t/out | FileCheck --check-prefix=FLATSYM %s
+# RUN: llvm-readobj --syms %t/out | FileCheck --check-prefix=FLATSYM-READOBJ %s
+
+# HEADERBITS-NOT: NOUNDEFS
+# HEADERBITS-NOT: TWOLEVEL
+# HEADERBITS: DYLDLINK
+# HEADERBITS-NOT: foo.dylib
+# HEADERBITS-NOT: bar.dylib
+
+# FLAT: Bind table:
+# FLAT: __DATA_CONST __got 0x{{[0-9a-f]*}} pointer 0 flat-namespace dyld_stub_binder
+# FLAT: Lazy bind table:
+# FLAT-DAG: __DATA __la_symbol_ptr 0x{{[0-9a-f]*}} flat-namespace _bar
+# FLAT-DAG: __DATA __la_symbol_ptr 0x{{[0-9a-f]*}} flat-namespace _baz
+# FLAT-DAG: __DATA __la_symbol_ptr 0x{{[0-9a-f]*}} flat-namespace _foo
+
+# No "(dynamically looked up)" because llvm-nm -m doesn't print that
+# for files without MH_TWOLEVEL for some reason.
+# FLATSYM: (undefined) external _bar
+# FLATSYM: (undefined) external _baz
+# FLATSYM: (undefined) external _foo
+
+# ...but `llvm-readobj --syms` does, so verify we put the right thing there.
+# FLATSYM-READOBJ: Flags [ (0xFE00)
+
+# Undefined symbols should still cause errors by default.
+# RUN: llvm-mc -filetype=obj -triple=x86_64-apple-macos \
+# RUN: -o %t/main-with-undef.o %t/main-with-undef.s
+# RUN: not %lld -flat_namespace -lSystem %t/main-with-undef.o %t/bar.dylib \
+# RUN: -o %t/out 2>&1 | FileCheck --check-prefix=UNDEF %s
+# UNDEF: error: undefined symbol: _quux
+
+#--- foo.s
+.globl _foo
+_foo:
+ ret
+
+#--- bar.s
+.globl _bar
+_bar:
+ callq _foo
+ ret
+
+#--- baz.s
+.globl _baz
+_baz:
+ callq _bar
+ ret
+
+#--- main.s
+.globl _main
+_main:
+ callq _foo
+ callq _bar
+ callq _baz
+ ret
+
+#--- main-with-undef.s
+.globl _main
+_main:
+ callq _foo
+ callq _bar
+ callq _baz
+ callq _quux
+ ret
diff --git a/test/MachO/header.s b/test/MachO/header.s
index 405fabc..4264893 100644
--- a/test/MachO/header.s
+++ b/test/MachO/header.s
@@ -12,8 +12,8 @@
# RUN: llvm-objdump --macho --all-headers %t/x86-64-dylib | FileCheck %s -DCAPS=0x00
# RUN: llvm-objdump --macho --all-headers %t/arm64-dylib | FileCheck %s -DCAPS=0x00
-# CHECK: magic cputype cpusubtype caps filetype
-# CHECK-NEXT: MH_MAGIC_64 {{.*}} ALL [[CAPS]] {{.*}}
+# CHECK: magic cputype cpusubtype caps filetype {{.*}} flags
+# CHECK-NEXT: MH_MAGIC_64 {{.*}} ALL [[CAPS]] {{.*}} NOUNDEFS {{.*}} TWOLEVEL
.globl _main
_main:
