[lld] 66f3400 - [lld-macho] Define __mh_*_header synthetic symbols.
Vy Nguyen via llvm-commits
llvm-commits at lists.llvm.org
Fri Mar 19 11:15:47 PDT 2021
Author: Vy Nguyen
Date: 2021-03-19T14:14:40-04:00
New Revision: 66f340051ac2d334f30ef85251323b12cb2e6e5f
URL: https://github.com/llvm/llvm-project/commit/66f340051ac2d334f30ef85251323b12cb2e6e5f
DIFF: https://github.com/llvm/llvm-project/commit/66f340051ac2d334f30ef85251323b12cb2e6e5f.diff
LOG: [lld-macho] Define __mh_*_header synthetic symbols.
Bug: https://bugs.llvm.org/show_bug.cgi?id=49290
Differential Revision: https://reviews.llvm.org/D97007
Added:
lld/test/MachO/mh-execute-header.s
lld/test/MachO/mh-header-link.s
Modified:
lld/MachO/Driver.cpp
lld/MachO/SymbolTable.cpp
lld/MachO/SymbolTable.h
lld/MachO/Symbols.h
lld/MachO/SyntheticSections.cpp
lld/MachO/SyntheticSections.h
lld/MachO/Writer.cpp
lld/test/MachO/export-trie.s
lld/test/MachO/map-file.s
lld/test/MachO/objc.s
lld/test/MachO/stabs.s
lld/test/MachO/symtab.s
Removed:
################################################################################
diff --git a/lld/MachO/Driver.cpp b/lld/MachO/Driver.cpp
index c85b72564213..341ddaf870a6 100644
--- a/lld/MachO/Driver.cpp
+++ b/lld/MachO/Driver.cpp
@@ -1043,14 +1043,7 @@ bool macho::link(ArrayRef<const char *> argsArr, bool canExitEarly,
}
createSyntheticSections();
-
- // The Itanium C++ ABI requires dylibs to pass a pointer to __cxa_atexit
- // which does e.g. cleanup of static global variables. The ABI document says
- // that the pointer can point to any address in one of the dylib's segments,
- // but in practice ld64 seems to set it to point to the header, so that's
- // what's implemented here.
- symtab->addSynthetic("___dso_handle", in.header->isec, 0,
- /*privateExtern=*/true, /*linkerInternal=*/true);
+ createSyntheticSymbols();
for (const Arg *arg : args.filtered(OPT_sectcreate)) {
StringRef segName = arg->getValue(0);
diff --git a/lld/MachO/SymbolTable.cpp b/lld/MachO/SymbolTable.cpp
index 1d812538005d..311c0018379d 100644
--- a/lld/MachO/SymbolTable.cpp
+++ b/lld/MachO/SymbolTable.cpp
@@ -159,10 +159,10 @@ Symbol *SymbolTable::addLazy(StringRef name, ArchiveFile *file,
Defined *SymbolTable::addSynthetic(StringRef name, InputSection *isec,
uint32_t value, bool isPrivateExtern,
- bool isLinkerInternal) {
- Defined *s = addDefined(name, nullptr, isec, value, /*isWeakDef=*/false,
- isPrivateExtern);
- s->linkerInternal = isLinkerInternal;
+ bool includeInSymtab) {
+ Defined *s = addDefined(name, nullptr, isec, value,
+ /*isWeakDef=*/false, isPrivateExtern);
+ s->includeInSymtab = includeInSymtab;
return s;
}
diff --git a/lld/MachO/SymbolTable.h b/lld/MachO/SymbolTable.h
index 8964713c7a74..9aed8c90064f 100644
--- a/lld/MachO/SymbolTable.h
+++ b/lld/MachO/SymbolTable.h
@@ -9,6 +9,8 @@
#ifndef LLD_MACHO_SYMBOL_TABLE_H
#define LLD_MACHO_SYMBOL_TABLE_H
+#include "Symbols.h"
+
#include "lld/Common/LLVM.h"
#include "llvm/ADT/CachedHashString.h"
#include "llvm/ADT/DenseMap.h"
@@ -50,7 +52,7 @@ class SymbolTable {
const llvm::object::Archive::Symbol &sym);
Defined *addSynthetic(StringRef name, InputSection *, uint32_t value,
- bool isPrivateExtern, bool isLinkerInternal);
+ bool isPrivateExtern, bool includeInSymtab);
ArrayRef<Symbol *> getSymbols() const { return symVector; }
Symbol *find(llvm::CachedHashStringRef name);
diff --git a/lld/MachO/Symbols.h b/lld/MachO/Symbols.h
index ada5bc164c82..e815b7de9c20 100644
--- a/lld/MachO/Symbols.h
+++ b/lld/MachO/Symbols.h
@@ -99,7 +99,7 @@ class Defined : public Symbol {
bool isWeakDef, bool isExternal, bool isPrivateExtern)
: Symbol(DefinedKind, name, file), isec(isec), value(value),
overridesWeakDef(false), privateExtern(isPrivateExtern),
- linkerInternal(false), weakDef(isWeakDef), external(isExternal) {}
+ includeInSymtab(true), weakDef(isWeakDef), external(isExternal) {}
bool isWeakDef() const override { return weakDef; }
bool isExternalWeakDef() const {
@@ -124,8 +124,8 @@ class Defined : public Symbol {
bool overridesWeakDef : 1;
// Whether this symbol should appear in the output binary's export trie.
bool privateExtern : 1;
- // Whether this symbol should appear in the output binary's symbol table.
- bool linkerInternal : 1;
+ // Whether this symbol should appear in the output symbol table.
+ bool includeInSymtab : 1;
private:
const bool weakDef : 1;
diff --git a/lld/MachO/SyntheticSections.cpp b/lld/MachO/SyntheticSections.cpp
index 1834a48f0e56..cf7d40398e62 100644
--- a/lld/MachO/SyntheticSections.cpp
+++ b/lld/MachO/SyntheticSections.cpp
@@ -53,7 +53,12 @@ SyntheticSection::SyntheticSection(const char *segname, const char *name)
// dyld3's MachOLoaded::getSlide() assumes that the __TEXT segment starts
// from the beginning of the file (i.e. the header).
MachHeaderSection::MachHeaderSection()
- : SyntheticSection(segment_names::text, section_names::header) {}
+ : SyntheticSection(segment_names::text, section_names::header) {
+ // XXX: This is a hack. (See D97007)
+ // Setting the index to 1 to pretend that this section is the text
+ // section.
+ index = 1;
+}
void MachHeaderSection::addLoadCommand(LoadCommand *lc) {
loadCommands.push_back(lc);
@@ -754,7 +759,7 @@ void SymtabSection::finalizeContents() {
for (Symbol *sym : symtab->getSymbols()) {
if (auto *defined = dyn_cast<Defined>(sym)) {
- if (defined->linkerInternal)
+ if (!defined->includeInSymtab)
continue;
assert(defined->isExternal());
addSymbol(externalSymbols, defined);
@@ -993,3 +998,56 @@ void CodeSignatureSection::writeTo(uint8_t *buf) const {
memcpy(id, fileName.begin(), fileName.size());
memset(id + fileName.size(), 0, fileNamePad);
}
+
+void macho::createSyntheticSymbols() {
+ auto addHeaderSymbol = [](const char *name) {
+ symtab->addSynthetic(name, in.header->isec, 0,
+ /*privateExtern=*/true,
+ /*includeInSymtab*/ false);
+ };
+
+ switch (config->outputType) {
+ // FIXME: Assign the right addresse value for these symbols
+ // (rather than 0). But we need to do that after assignAddresses().
+ case MH_EXECUTE:
+ // If linking PIE, __mh_execute_header is a defined symbol in
+ // __TEXT, __text)
+ // Otherwise, it's an absolute symbol.
+ if (config->isPic)
+ symtab->addSynthetic("__mh_execute_header", in.header->isec, 0,
+ /*privateExtern*/ false,
+ /*includeInSymbtab*/ true);
+ else
+ symtab->addSynthetic("__mh_execute_header",
+ /*isec*/ nullptr, 0,
+ /*privateExtern*/ false,
+ /*includeInSymbtab*/ true);
+ break;
+
+ // The following symbols are N_SECT symbols, even though the header is not
+ // part of any section and that they are private to the bundle/dylib/object
+ // they are part of.
+ case MH_BUNDLE:
+ addHeaderSymbol("__mh_bundle_header");
+ break;
+ case MH_DYLIB:
+ addHeaderSymbol("__mh_dylib_header");
+ break;
+ case MH_DYLINKER:
+ addHeaderSymbol("__mh_dylinker_header");
+ break;
+ case MH_OBJECT:
+ addHeaderSymbol("__mh_object_header");
+ break;
+ default:
+ llvm_unreachable("unexpected outputType");
+ break;
+ }
+
+ // The Itanium C++ ABI requires dylibs to pass a pointer to __cxa_atexit
+ // which does e.g. cleanup of static global variables. The ABI document
+ // says that the pointer can point to any address in one of the dylib's
+ // segments, but in practice ld64 seems to set it to point to the header,
+ // so that's what's implemented here.
+ addHeaderSymbol("___dso_handle");
+}
diff --git a/lld/MachO/SyntheticSections.h b/lld/MachO/SyntheticSections.h
index 74a6d3c9475c..92869476390a 100644
--- a/lld/MachO/SyntheticSections.h
+++ b/lld/MachO/SyntheticSections.h
@@ -500,6 +500,8 @@ struct InStruct {
extern InStruct in;
extern std::vector<SyntheticSection *> syntheticSections;
+void createSyntheticSymbols();
+
} // namespace macho
} // namespace lld
diff --git a/lld/MachO/Writer.cpp b/lld/MachO/Writer.cpp
index b2d316355807..4070a2077937 100644
--- a/lld/MachO/Writer.cpp
+++ b/lld/MachO/Writer.cpp
@@ -751,7 +751,6 @@ static void sortSegmentsAndSections() {
// output section indices.
if (!osec->isHidden())
osec->index = ++sectionIndex;
-
if (!firstTLVDataSection && isThreadLocalData(osec->flags))
firstTLVDataSection = osec;
diff --git a/lld/test/MachO/export-trie.s b/lld/test/MachO/export-trie.s
index c479e166561c..cab8312fe1d0 100644
--- a/lld/test/MachO/export-trie.s
+++ b/lld/test/MachO/export-trie.s
@@ -15,7 +15,9 @@
# EXPORTS-DAG: [[#%x, HELLO_WORLD_ADDR:]] {{.*}} _hello_world
# EXPORTS-DAG: [[#%x, HELLO_ITS_ME_ADDR:]] {{.*}} _hello_its_me
# EXPORTS-DAG: [[#%x, HELLO_ITS_YOU_ADDR:]] {{.*}} _hello_its_you
+# EXPORTS-DAG: {{0+}} g *ABS* __mh_execute_header
# EXPORTS-LABEL: Exports trie:
+# EXPORTS-DAG: 0x{{0+}} __mh_execute_header [absolute]
# EXPORTS-DAG: 0x{{0*}}[[#%X, MAIN_ADDR]] _main
# EXPORTS-DAG: 0x{{0*}}[[#%X, HELLO_ADDR]] _hello
# EXPORTS-DAG: 0x{{0*}}[[#%X, HELLO_WORLD_ADDR]] _hello_world
@@ -27,13 +29,16 @@
# CHECK-LABEL: ExportTrie:
# CHECK: Name: ''
# CHECK: Name: _
-# CHECK: Name: main
-# CHECK: Name: hello
+# CHECK-DAG: Name: _mh_execute_header
+# CHECK-DAG: Name: main
+# CHECK-DAG: Name: hello
# CHECK: Name: _
# CHECK: Name: world
# CHECK: Name: its_
-# CHECK: Name: you
-# CHECK: Name: me
+# CHECK-DAG: Name: you
+# CHECK-DAG: Name: me
+
+
.section __TEXT,__cstring
.globl _hello, _hello_world, _hello_its_me, _hello_its_you, _main
diff --git a/lld/test/MachO/map-file.s b/lld/test/MachO/map-file.s
index ac5fb93898d3..215d193aa622 100644
--- a/lld/test/MachO/map-file.s
+++ b/lld/test/MachO/map-file.s
@@ -29,6 +29,7 @@ _main:
# CHECK-NEXT: [[#%x,MAIN:]] g F __TEXT,__text _main
# CHECK-NEXT: [[#%x,NUMBER:]] g O __DATA,__common _number
# CHECK-NEXT: [[#%x,FOO:]] g O __TEXT,obj _foo
+# CHECK-NEXT: {{0+}} g *ABS* __mh_execute_header
# CHECK-NEXT: # Path: {{.*}}{{/|\\}}map-file.s.tmp/test-map
# CHECK-NEXT: # Arch: x86_64
diff --git a/lld/test/MachO/mh-execute-header.s b/lld/test/MachO/mh-execute-header.s
new file mode 100644
index 000000000000..4a62b27bb8fa
--- /dev/null
+++ b/lld/test/MachO/mh-execute-header.s
@@ -0,0 +1,16 @@
+# REQUIRES: x86
+# RUN: rm -rf %t; mkdir %t
+# RUN: llvm-mc -filetype=obj -triple=x86_64-apple-darwin %s -o %t/test.o
+# RUN: %lld -o %t/test.pie %t/test.o -pie
+# RUN: llvm-objdump --macho --syms %t/test.pie | FileCheck %s --check-prefix=PIE
+
+# RUN: %lld -o %t/test.no_pie %t/test.o -no_pie
+# RUN: llvm-objdump --macho --syms %t/test.no_pie | FileCheck %s --check-prefix=NO-PIE
+
+# PIE: 0000000100000000 g F __TEXT,__text __mh_execute_header
+# NO-PIE: 0000000000000000 g *ABS* __mh_execute_header
+
+.text
+.global _main
+_main:
+ ret
diff --git a/lld/test/MachO/mh-header-link.s b/lld/test/MachO/mh-header-link.s
new file mode 100644
index 000000000000..0813435397b7
--- /dev/null
+++ b/lld/test/MachO/mh-header-link.s
@@ -0,0 +1,43 @@
+# REQUIRES: x86
+
+## This tests that we can link against these synthetic symbols even
+## if they are not in the symbol table.
+
+# RUN: rm -rf %t; split-file %s %t
+
+## Test that in a dylib, we can link against __mh_dylib_header
+## (but not in other types of files)
+
+# RUN: llvm-mc %t/dylib.s -triple=x86_64-apple-macos11.0 -filetype=obj -o %t/dylib.o
+# RUN: %lld -pie -dylib %t/dylib.o -o %t/dylib.out
+# RUN: llvm-objdump -m --syms %t/dylib.out | FileCheck %s --check-prefix DYLIB
+
+# RUN: not %lld -pie -o /dev/null %t/dylib.o 2>&1 | FileCheck %s --check-prefix ERR-DYLIB
+
+# DYLIB: SYMBOL TABLE:
+# DYLIB-NEXT: {{[0-9a-f]+}} g F __TEXT,__text _main
+# DYLIB-NEXT-EMPTY:
+# ERR-DYLIB: error: undefined symbol: __mh_dylib_header
+
+## Test that in an executable, we can link against __mh_execute_header
+# RUN: llvm-mc %t/main.s -triple=x86_64-apple-macos11.0 -filetype=obj -o %t/exec.o
+# RUN: %lld -pie %t/exec.o -o %t/exec.out
+
+## But it would be an error trying to reference __mh_execute_header in a dylib
+# RUN: not %lld -pie -o /dev/null -dylib %t/exec.o 2>&1 | FileCheck %s --check-prefix ERR-EXEC
+
+# ERR-EXEC: error: undefined symbol: __mh_execute_header
+
+#--- main.s
+.text
+.globl _main
+_main:
+ mov __mh_execute_header at GOTPCREL(%rip), %rax
+ ret
+
+#--- dylib.s
+.text
+.globl _main
+_main:
+ mov __mh_dylib_header at GOTPCREL(%rip), %rax
+ ret
diff --git a/lld/test/MachO/objc.s b/lld/test/MachO/objc.s
index 53dd12e8f190..06f47d2c3b78 100644
--- a/lld/test/MachO/objc.s
+++ b/lld/test/MachO/objc.s
@@ -32,7 +32,7 @@
# NO-OBJC-EMPTY:
# NO-OBJC-NEXT: SYMBOL TABLE:
# NO-OBJC-NEXT: g F __TEXT,__text _main
-# NO-OBJC-EMPTY:
+# NO_OBJC-NEXT: g *ABS* __mh_execute_header
#--- has-objc-symbol.s
.globl _OBJC_CLASS_$_MyObject
diff --git a/lld/test/MachO/stabs.s b/lld/test/MachO/stabs.s
index 09735feb5b26..6a72ff246e1d 100644
--- a/lld/test/MachO/stabs.s
+++ b/lld/test/MachO/stabs.s
@@ -60,6 +60,7 @@
# CHECK-NEXT: [[#ZERO]] S _zero
# CHECK-NEXT: [[#FOO]] T _foo
# CHECK-NEXT: {{[0-9af]+}} T _no_debug
+# CHECK-NEXT: {{0+}} A __mh_execute_header
# CHECK-EMPTY:
## Check that we don't attempt to emit rebase opcodes for the debug sections
diff --git a/lld/test/MachO/symtab.s b/lld/test/MachO/symtab.s
index 44d42068ffb5..35fc961d1b35 100644
--- a/lld/test/MachO/symtab.s
+++ b/lld/test/MachO/symtab.s
@@ -56,6 +56,16 @@
# CHECK-NEXT: ]
# CHECK-NEXT: Value: 0x1{{[0-9a-f]*}}
# CHECK-NEXT: }
+# CHECK-NEXT: Symbol {
+# CHECK-NEXT: Name: __mh_execute_header (81)
+# CHECK-NEXT: Extern
+# CHECK-NEXT: Type: Abs (0x2)
+# CHECK-NEXT: Section: (0x0)
+# CHECK-NEXT: RefType: UndefinedNonLazy (0x0)
+# CHECK-NEXT: Flags [ (0x0)
+# CHECK-NEXT: ]
+# CHECK-NEXT: Value: 0x0
+# CHECK-NEXT: }
# CHECK-NEXT: Symbol {
# CHECK-NEXT: Name: dyld_stub_binder
# CHECK-NEXT: Extern
@@ -82,8 +92,8 @@
# CHECK-NEXT: ilocalsym: 0
# CHECK-NEXT: nlocalsym: 2
# CHECK-NEXT: iextdefsym: 2
-# CHECK-NEXT: nextdefsym: 3
-# CHECK-NEXT: iundefsym: 5
+# CHECK-NEXT: nextdefsym: 4
+# CHECK-NEXT: iundefsym: 6
# CHECK-NEXT: nundefsym: 2
## Verify that the first entry in the StringTable is a space, and that
More information about the llvm-commits
mailing list