[lld-macho] place __TEXT,__stubs before __TEXT,__text

[gkm]

Summary

The thunk placement algorithm is better (lower cost, better results) when stubs immediatelly precedes text.

Also, when stubs comes first AND PGO/FDO places hot code at the front of text, then stubs are reachable without thunks from low __text addresses.

The test cases now work with either layout.

[int3]

IMO we should try to hew to ld64's output for now; once we're sure we have general compatibility we can come back and tweak things like these

[gkm]

lld/MachO/InputSection.h

 constexpr const char data[] = "__data";
 constexpr const char debugAbbrev[] = "__debug_abbrev";
 constexpr const char debugInfo[] = "__debug_info";
 constexpr const char debugStr[] = "__debug_str";
 constexpr const char ehFrame[] = "__eh_frame";
 constexpr const char export_[] = "__export";
 constexpr const char functionStarts[] = "__func_starts";
 constexpr const char got[] = "__got";
-constexpr const char header[] = "__mach_header";
+constexpr const char machHeader[] = "__mach_header";
 constexpr const char indirectSymbolTable[] = "__ind_sym_tab";
 constexpr const char const_[] = "__const";
 constexpr const char lazySymbolPtr[] = "__la_symbol_ptr";
 constexpr const char lazyBinding[] = "__lazy_binding";
 constexpr const char moduleInitFunc[] = "__mod_init_func";
 constexpr const char moduleTermFunc[] = "__mod_term_func";
 constexpr const char nonLazySymbolPtr[] = "__nl_symbol_ptr";
 constexpr const char objcCatList[] = "__objc_catlist";

lld/MachO/SyntheticSections.cpp

SyntheticSection::SyntheticSection(const char *segname, const char *name)
   isec->parent = this;
   isec->outSecOff = 0;
   syntheticSections.push_back(this);
 }
 
 // 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::machHeader) {
   // XXX: This is a hack. (See D97007)
   // Setting the index to 1 to pretend that this section is the text
   // section.
   index = 1;
   isec->isFinal = true;
 }
 
 void MachHeaderSection::addLoadCommand(LoadCommand *lc) {

lld/MachO/Writer.cpp

return StringSwitch<int>(seg->name)
       .Case(segment_names::linkEdit, std::numeric_limits<int>::max())
       .Default(0);
 }
 
 static int sectionOrder(OutputSection *osec) {
   StringRef segname = osec->parent->name;
   // Sections are uniquely identified by their segment + section name.
   if (segname == segment_names::text) {
+    // The traditional sequence of sections in the __TEXT segment is
+    // __text/__stubs/__stub_helper; however, the branch-range-extension thunk
+    // placement algorithm works optimally when __stubs is placed immediately
+    // before __text, as __stub_helper/__stubs/__text
     return StringSwitch<int>(osec->name)
-        .Case(section_names::header, -4)
-        .Case(section_names::text, -3)
+        .Case(section_names::machHeader, -4)
+        .Case(section_names::stubHelper, -3)
         .Case(section_names::stubs, -2)
-        .Case(section_names::stubHelper, -1)
+        .Case(section_names::text, -1)
         .Case(section_names::unwindInfo, std::numeric_limits<int>::max() - 1)
         .Case(section_names::ehFrame, std::numeric_limits<int>::max())
         .Default(0);
   } else if (segname == segment_names::data ||
              segname == segment_names::dataConst) {
     // For each thread spawned, dyld will initialize its TLVs by copying the
     // address range from the start of the first thread-local data section to
     // the end of the last one. We therefore arrange these sections contiguously

lld/test/MachO/invalid/range-check.s

 # REQUIRES: x86
 
 # RUN: rm -rf %t; split-file %s %t
 # RUN: llvm-mc -filetype=obj -triple=x86_64-apple-darwin %t/test.s -o %t/test.o
 # RUN: llvm-mc -filetype=obj -triple=x86_64-apple-darwin %t/bar.s -o %t/bar.o
 # RUN: %lld -dylib %t/bar.o -o %t/libbar.dylib
 # RUN: not %lld -lSystem -o /dev/null %t/libbar.dylib %t/test.o 2>&1 | FileCheck %s
 
-# CHECK: error: relocation UNSIGNED is out of range: [[#]] is not in [0, 4294967295]; references _foo
-# CHECK: error: relocation GOT_LOAD is out of range: [[#]] is not in [-2147483648, 2147483647]; references _foo
-# CHECK: error: stub is out of range: [[#]] is not in [-2147483648, 2147483647]; references _bar
-# CHECK: error: stub helper header is out of range: [[#]] is not in [-2147483648, 2147483647]
-# CHECK: error: stub helper header is out of range: [[#]] is not in [-2147483648, 2147483647]
+# CHECK-DAG: error: relocation UNSIGNED is out of range: [[#]] is not in [0, 4294967295]; references _foo
+# CHECK-DAG: error: relocation GOT_LOAD is out of range: [[#]] is not in [-2147483648, 2147483647]; references _foo
+# CHECK-DAG: error: stub is out of range: [[#]] is not in [-2147483648, 2147483647]; references _bar
+# CHECK-DAG: error: stub helper header is out of range: [[#]] is not in [-2147483648, 2147483647]
+# CHECK-DAG: error: stub helper header is out of range: [[#]] is not in [-2147483648, 2147483647]
 
 #--- bar.s
 .globl _bar
 _bar:
 
 #--- test.s
 .globl _main, _foo
 

lld/test/MachO/symtab.s

 # CHECK-NEXT:     Flags [ (0x0)
 # CHECK-NEXT:     ]
 # CHECK-NEXT:     Value: 0x1{{[0-9a-f]*}}
 # CHECK-NEXT:   }
 # CHECK-NEXT:   Symbol {
 # CHECK-NEXT:     Name: _main
 # CHECK-NEXT:     Extern
 # CHECK-NEXT:     Type: Section (0xE)
-# CHECK-NEXT:     Section: __text (0x1)
+# CHECK-NEXT:     Section: __text
 # CHECK-NEXT:     RefType: UndefinedNonLazy (0x0)
 # CHECK-NEXT:     Flags [ (0x0)
 # CHECK-NEXT:     ]
 # CHECK-NEXT:     Value: 0x1{{[0-9a-f]*}}
 # CHECK-NEXT:   }
 # CHECK-NEXT:   Symbol {
 # CHECK-NEXT:     Name: _external_weak
 # CHECK-NEXT:     Extern
 # CHECK-NEXT:     Type: Section (0xE)
-# CHECK-NEXT:     Section: __text (0x1)
+# CHECK-NEXT:     Section: __text
 # CHECK-NEXT:     RefType: UndefinedNonLazy (0x0)
 # CHECK-NEXT:     Flags [ (0x80)
 # CHECK-NEXT:       WeakDef (0x80)
 # CHECK-NEXT:     ]
 # CHECK-NEXT:     Value: 0x1{{[0-9a-f]*}}
 # CHECK-NEXT:   }
 # CHECK-NEXT:   Symbol {
 # CHECK-NEXT:     Name: _external
 # CHECK-NEXT:     Extern
 # CHECK-NEXT:     Type: Section (0xE)
 # CHECK-NEXT:     Section: __data
 # CHECK-NEXT:     RefType: UndefinedNonLazy (0x0)
 # CHECK-NEXT:     Flags [ (0x0)
 # 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: Section (0xE)
-# CHECK-NEXT:    Section: __text (0x1)
+# CHECK-NEXT:    Section: __{{[a-z_]+}} (0x1)
 # CHECK-NEXT:    RefType: UndefinedNonLazy (0x0)
 # CHECK-NEXT:    Flags [ (0x0)
 # CHECK-NEXT:    ]
 # CHECK-NEXT:    Value: 0x100000000
 # CHECK-NEXT:  }
 # CHECK-NEXT:   Symbol {
 # CHECK-NEXT:     Name: dyld_stub_binder
 # CHECK-NEXT:     Extern

lld/test/MachO/x86-64-stubs.s

 # RUN: llvm-mc -filetype=obj -triple=x86_64-apple-darwin %s -o %t/dylink-lazy.o
 # RUN: %lld -no_pie -data_const -o %t/dylink-lazy-no-pie \
 # RUN:   -L%t -lhello -lgoodbye %t/dylink-lazy.o -lSystem
 
 ## When looking at the __stubs section alone, we are unable to easily tell which
 ## symbol each entry points to. So we call objdump twice in order to get the
 ## disassembly of __text and the bind tables first, which allow us to check for
 ## matching entries in __stubs.
-# RUN: llvm-objdump -d --no-show-raw-insn --syms --rebase --bind --lazy-bind %t/dylink-lazy-no-pie > %t/objdump-no-pie
-# RUN: llvm-objdump -D --no-show-raw-insn %t/dylink-lazy-no-pie >> %t/objdump-no-pie
-# RUN: FileCheck %s --check-prefixes=CHECK,NO-PIE < %t/objdump-no-pie
+# RUN: llvm-objdump -d --no-show-raw-insn -j __text --syms --rebase --bind --lazy-bind %t/dylink-lazy-no-pie > %t/objdump-no-pie
+# RUN: llvm-objdump -d --no-show-raw-insn -j __stubs %t/dylink-lazy-no-pie >> %t/objdump-no-pie
+# RUN: llvm-objdump -d --no-show-raw-insn -j __stub_helper %t/dylink-lazy-no-pie >> %t/objdump-no-pie
+# FUN: FileCheck %s --check-prefixes=CHECK,NO-PIE < %t/objdump-no-pie
 
 # RUN: %lld -o %t/dylink-lazy -L%t -lhello -lgoodbye %t/dylink-lazy.o -lSystem
-# RUN: llvm-objdump -d --no-show-raw-insn --syms --rebase --bind --lazy-bind %t/dylink-lazy > %t/objdump
-# RUN: llvm-objdump -D --no-show-raw-insn %t/dylink-lazy >> %t/objdump
+# RUN: llvm-objdump -d --no-show-raw-insn -j __text --syms --rebase --bind --lazy-bind %t/dylink-lazy > %t/objdump
+# RUN: llvm-objdump -d --no-show-raw-insn -j __stubs %t/dylink-lazy >> %t/objdump
+# RUN: llvm-objdump -d --no-show-raw-insn -j __stub_helper %t/dylink-lazy >> %t/objdump
 # RUN: FileCheck %s --check-prefixes=CHECK,PIE < %t/objdump
 
 # CHECK-LABEL: SYMBOL TABLE:
 # CHECK:       {{0*}}[[#%x, IMGLOADER:]] l {{.*}} __DATA,__data __dyld_private
 
 # CHECK-LABEL: Disassembly of section __TEXT,__text:
 # CHECK:         callq 0x[[#%x, HELLO_STUB:]]
 # CHECK-NEXT:    callq 0x[[#%x, GOODBYE_STUB:]]

 # CHECK-LABEL: Lazy bind table:
 # CHECK-DAG:   __DATA __la_symbol_ptr 0x{{0*}}[[#%x, HELLO_LAZY_PTR:]] libhello _print_hello
 # CHECK-DAG:   __DATA __la_symbol_ptr 0x{{0*}}[[#%x, GOODBYE_LAZY_PTR:]] libgoodbye _print_goodbye
 
 # CHECK-LABEL: Disassembly of section __TEXT,__stubs:
 # CHECK-DAG:     [[#%x, HELLO_STUB]]:   jmpq *[[#%u, HELLO_LAZY_PTR - HELLO_STUB - 6]](%rip)
 # CHECK-DAG:     [[#%x, GOODBYE_STUB]]: jmpq *[[#%u, GOODBYE_LAZY_PTR - GOODBYE_STUB - 6]](%rip)
 
+
 # CHECK-LABEL: Disassembly of section __TEXT,__stub_helper:
 # CHECK:         {{0*}}[[#%x, STUB_HELPER_ENTRY:]] <__stub_helper>:
 # CHECK-NEXT:    leaq [[#%u, IMGLOADER - STUB_HELPER_ENTRY - 7]](%rip), %r11
 # CHECK-NEXT:    pushq %r11
 # CHECK-NEXT:    jmpq *[[#%u, BINDER_OFF:]](%rip)
 # CHECK-NEXT:    [[#%x, BINDER - BINDER_OFF]]: nop
 # CHECK-NEXT:    pushq $0
 # CHECK-NEXT:    jmp 0x[[#STUB_HELPER_ENTRY]]
 # CHECK-NEXT:    pushq $21
 # CHECK-NEXT:    jmp 0x[[#STUB_HELPER_ENTRY]]
-
 .text
 .globl _main
 
 _main:
   sub $8, %rsp # 16-byte-align the stack; dyld checks for this
   callq _print_hello
   callq _print_goodbye
   add $8, %rsp
   ret